Coordinated by CRHEA-CNRS research laboratory, this monthly newsletter is produced by Knowmade with collaboration from the managers of GANEX groups. The newsletter presents a selection of newest scientific publications, patent applications and press releases related to III-Nitride semiconductor materials (GaN, AlN, InN and alloys)

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GANEX Newsletter No. 45 October 2016

III-N Technology

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GANEX | Newsletter No. 45 - III-N Technology 2

METHODOLOGY

Each month

250+ new scientific publications

120+ new patent applications

20+ new press releases

Sources 10+ scientific journal editors

Elsevier, IOP, IEEE, Wiley, Springer, APS, AIP, AVS, ECS, Nature, Science …

10+ specialist magazines Semiconductor Today, ElectoIQ, i-micronews,

Compound Semiconductor, Solid State Technology … 5+ open access database: FreeFulPDF, DOAJ …

Patent database: Questel-Orbit

Selection by III-N French

experts

GANEX monthly newsletter

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GANEX | Newsletter No. 45 - III-N Technology 3

TABLE OF CONTENTS (clickable links to chapters)

SCIENTIFIC PUBLICATION ................................................................................................................... 4

GROUP 1 - LEDs and Lighting ................................................................................................................... 4

GROUP 2 - Laser and Coherent Light ....................................................................................................... 8

GROUP 3 - Power Electronics ................................................................................................................. 11

GROUP 4 - Advanced Electronics and RF ............................................................................................... 20

GROUP 5 – MEMS and Sensors .............................................................................................................. 24

GROUP 6 - Photovoltaics and Energy harvesting ................................................................................... 26

GROUP 7 - Materials, Technology and Fundamental............................................................................. 27

PRESS RELEASE ................................................................................................................................ 37

PATENT APPLICATION ...................................................................................................................... 51

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GANEX | Newsletter No. 45 - III-N Technology 4

SCIENTIFIC PUBLICATION Selection of new scientific articles

GROUP 1 - LEDs and Lighting Group leader: Benjamin Damilano (CRHEA-CNRS)

Information selected by Benjamin Damilano (CRHEA-CNRS)

Photoelectrochemical liftoff of LEDs grown on freestanding c-plane GaN substrates Materials Department, University of California, Santa Barbara, CA 93106, USA Optics Express https://doi.org/10.1364/OE.24.022875

We demonstrate a thin-film flip-chip (TFFC) process for LEDs grown on freestanding c-plane GaN substrates. LEDs are transferred from a bulk GaN substrate to a sapphire submount via a photoelectrochemical (PEC) undercut etch. This PEC liftoff method allows for substrate reuse and exposes the N-face of the LEDs for additional roughening. The LEDs emitted at a wavelength of 432 nm with a turn on voltage of ~3 V. Etching the LEDs in heated KOH after transferring them to a sapphire submount increased the peak external quantum efficiency (EQE) by 42.5% from 9.9% (unintentionally roughened) to 14.1% (intentionally roughened). Performance enhancement of blue light-emitting diodes with InGaN/GaN multi-quantum wells grown on Si substrates by inserting thin AlGaN interlayers Corporate Research and Development Center, Toshiba Corporation, 1, Komukai-Toshiba-cho Saiwai-Ku, Kawasaki 212-8582, Japan J. Appl. Phys. http://dx.doi.org/10.1063/1.4962719

We have grown blue light-emitting diodes (LEDs) having InGaN/GaN multi-quantum wells (MQWs) with thin AlyGa1−yN (0 < y < 0.3) interlayers on Si(111) substrates. It was found by high-resolution transmission electron microscopy observations and three-dimensional atom probe analysis that 1-nm-thick interlayers with an AlN mole fraction of less than y = 0.3 were continuously formed between GaN barriers and InGaN wells, and that the AlN mole fraction up to y = 0.15 could be

consistently controlled. The external quantum efficiency of the blue LED was enhanced in the low-current-density region (≤45 A/cm2) but reduced in the high-current-density region by the insertion of the thin Al0.15Ga0.85N interlayers in the MQWs. We also found that reductions in both forward voltage and wavelength shift with current were achieved by inserting the interlayers even though the inserted AlGaN layers had potential higher than that of the GaN barriers. The obtained peak wall-plug efficiency was 83% at room temperature. We suggest that the enhanced electroluminescence (EL) performance was caused by the introduction of polarization-induced hole carriers in the InGaN wells on the side adjacent to the thin AlGaN/InGaN interface and efficient electron carrier transport through multiple wells. This model is supported by temperature-dependent EL properties and band-diagram simulations. We also found that inserting the interlayers brought about a reduction in the Shockley-Read-Hall nonradiative recombination component, corresponding to the shrinkage of V-defects. This is another conceivable reason for the observed performance enhancement. Design and demonstration of ultra-wide bandgap AlGaN tunnel junctions Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4962900

Ultra violet light emitting diodes (UV LEDs) face critical limitations in both the injection efficiency and the light extraction efficiency due to the resistive and absorbing p-type contact layers. In this work, we investigate the design and application of polarization engineered tunnel junctions for ultra-wide bandgap AlGaN (Al mole fraction >50%) materials towards highly efficient UV LEDs. We demonstrate that polarization-

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GANEX | Newsletter No. 45 - III-N Technology 5

induced three dimensional charge is beneficial in reducing tunneling barriers especially for high composition AlGaN tunnel junctions. The design of graded tunnel junction structures could lead to low tunneling resistance below 10−3 Ω cm2 and low voltage consumption below 1 V (at 1 kA/cm2) for high composition AlGaN tunnel junctions. Experimental demonstration of 292 nm emission was achieved through non-equilibrium hole injection into wide bandgap materials with bandgap energy larger than 4.7 eV, and detailed modeling of tunnel junctions shows that they can be engineered to have low resistance and can enable efficient emitters in the UV-C wavelength range. Thermal Inductance in GaN Devices Key Laboratory of Optoelectronic Technology & Systems, Education Ministry of China, Chongqing University, Chongqing 400044, China IEEE Electron Device Letters http://dx.doi.org/10.1109/LED.2016.2612243

Using the analogue of the electric inductance, we reveal the properties of the thermal inductance in GaN-based light-emitting diode (LED) devices by testing their transient thermal behaviours. We find that the devices exhibit a transient thermal response under step-down or step-up currents and observe notable inductive phenomena of the temperature response as time evolves from start up to some hundred microseconds. We define thermal inductance as the rapid change in device temperature that is opposite to the temperature change expected from the power input. These findings can promote new temperature measurements, and novel thermal analyses of high-frequency semiconductor devices that combining the thermal resistances, thermal capacitances, and thermal inductances. Effect of the Phosphor Permanent Substrate on the Angular CCT for White Thin-Film Flip-Chip Light-Emitting Diodes Analog Devices, Wilmington, MA, USA Department of Materials Science and Engineering, National Chung Hsing University, Taichung, Taiwan IEEE Transactions on Electron Devices http://dx.doi.org/10.1109/TED.2016.2600259

This paper developed a phosphor layer applied for thin-film flip-chip light-emitting diodes (TFFC-LEDs) to produce uniform phosphor-converted TFFC white LEDs (TFFC-WLEDs) by combination of laser liftoff, secondary transferring, and surface roughening process. The spin-coating method was used for phosphor layer fabrication onto a substrate to form the phosphor permanent substrate. The TFFC-LEDs were then bonded onto the permanent substrate. From the results, the blue TFFC GaN-based LED with roughened u-GaN surface on a glass substrate (TFRG-LED) demonstrated a 54.2% (at 350 mA) enhancement in light output power, compared with a blue flip-chip GaN-on-sapphire based LED. As the TFFC GaN/phosphor-/glass-based white LED with roughened u-GaN surface (TFRG-WLED) was operated at a forward-bias current of 350 mA, the enhancement of luminous flux was increased by 75.5%, compared with a TFFC GaN/phosphor template-/glass-based white LED. The angular correlated color temperature (CCT) deviation of a TFRG-WLED can be reduced to 1279 K in the range from −75° to +75° at 5000–6000 K application. The TFRG-WLED was fabricated on the glass substrate with the roughened u-GaN surface and the structure of phosphor layer closed to the u-GaN. These kinds of FRGB-WLED structure contribute to a better light extraction characteristic and a higher CCT stability. High Modulation Bandwidth of a Light-Emitting Diode With Surface Plasmon Coupling Department of Electrical Engineering, Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan IEEE Transactions on Electron Devices http://dx.doi.org/10.1109/TED.2016.2601604

The enhancement of the modulation bandwidth (MB) of a light-emitting diode (LED) by reducing its mesa size, decreasing its active layer thickness, and inducing surface plasmon (SP) coupling with its quantum well (QW) is illustrated. The results are demonstrated by comparing three different LED surface structures, including bare p-GaN surface, Ga-doped ZnO current-spreading layer, and Ag nanoparticles for inducing SP coupling. In a single-QW LED with a circular mesa of 10 μm in

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GANEX | Newsletter No. 45 - III-N Technology 6

radius, SP coupling leads to a record-high LED MB of 528.8 MHz in the visible range. A smaller RC time constant can generally lead to a higher MB. However, when the RC time constant is smaller than ∼0.2 ns, its effect for increasing MB saturates. The results also confirm that the MB is essentially proportional to the square roots of carrier decay rate and injected current density. Temperature-dependent efficiency droop analysis of InGaN MQW light-emitting diode with modified ABC model Department of Electronics and Communication Engineering, Karunya University, Coimbatore, India Journal of Computational Electronics http://dx.doi.org/10.1007/s10825-016-0904-4

In this work, the origin of the efficiency droop at high injection current in an InGaN multiple-quantum-well light-emitting diode is suggested to be saturation of the radiative efficiency and insufficient carrier injection efficiency. A simple internal quantum efficiency (IQE) estimation method is developed by modifying the conventional ABC model to include carrier leakage mechanisms such as thermionic emission and carrier overflow, to account for the carrier injection efficiency at high current densities. The results show that thermionic emission and carrier overflow play a dominant role in the carrier leakage mechanism at high injection current. The data obtained from this analysis enable inference of the temperature dependence of the radiative/nonradiative coefficients and carrier leakage mechanisms. In addition, the model predicts the temperature dependence and rationale behind the degradation of the IQE at higher injection currents. Furthermore, the modeled output results show good fit with experimental data. Electroluminescent cooling mechanism in InGaN/GaN light-emitting diodes NUSOD Institute LLC, Newark, USA Crosslight Software Inc., Vancouver, Canada Optical and Quantum Electronics http://dx.doi.org/10.1007/s11082-016-0729-1

GaN-based light-emitting diodes (LEDs) are able to emit photons of higher energy than the injected electrons, resulting in an above-unity electrical efficiency. This phenomenon is generally attributed to heat extraction from the crystal lattice. In good agreement with measurements, we investigate the microscopic mechanism and the magnitude of such electroluminescent cooling by advanced numerical simulation including all relevant heat transfer mechanisms. Peltier cooling near the InGaN light-emitting layer is found to reduce the internal LED temperature rise significantly. High-Brightness Polarized Green InGaN/GaN Light-Emitting Diode Structure with Al-Coated p-GaN Grating Jiangsu Provincial Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, §College of Engineering and Applied Sciences, and ∥Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia ACS Photonics http://dx.doi.org/10.1021/acsphotonics.6b00433

The potential of polarized light sources in liquid-crystal displays has been extensively pursued due to the large energy savings as compared to conventional light sources. Here, we demonstrate high-brightness polarized green light emission from an InGaN/GaN light-emitting diode (LED) structure by combining the strong coupling between surface plasmons (SPs) and multiple quantum wells and polarization effects of SPs. As compared to the as-grown LED structure, a significant enhancement is observed in the total light emission with a high polarization degree of 54%. This work might provide an efficient way to realize simple, compact, and high-efficiency polarized light emission devices for applications in electro-optical integration.

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GANEX | Newsletter No. 45 - III-N Technology 7

Monolithic integration of Si-MOSFET and GaN-LED using Si/SiO2/GaN-LED wafer Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, Toyohashi, Aichi 441-8580, Japan Applied Physics Express http://dx.doi.org/10.7567/APEX.9.104101

In this report, we present a monolithic integration method for a Si-MOSFET and a GaN-LED onto a Si/SiO2/GaN-LED wafer as an elemental technology for monolithic optoelectronic integrated circuits. To enable a Si-MOSFET device process, we investigated the thermal tolerance of a thin top-Si and GaN-LED layer on a Si/SiO2/GaN-LED wafer. The high thermal tolerance of the Si/SiO2/GaN-LED structure allowed for the monolithic integration of a Si n-MOSFET and a GaN-µLED without degrading the performance of either device. A GaN-µLED driver circuit was fabricated using a Si n-MOSFET and a µLED of 30 × 30 µm2, with the modulation bandwidth of the circuit estimated to be over 10 MHz.

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GANEX | Newsletter No. 45 - III-N Technology 8

GROUP 2 - Laser and Coherent Light Group leader: Bruno Gayral (CEA)

Information selected by Knowmade

Dynamic characteristics of 410 nm semipolar (202¯1¯) III-nitride laser diodes with a modulation bandwidth of over 5 GHz Materials Department, University of California, Santa Barbara, California 93106, USA Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4962430

The dynamic characteristics of III-nitride multi-quantum well laser diodes (LDs) emitting at 410 nm were investigated. LDs were grown on semipolar (202¯1¯)(202¯1¯) bulk GaN substrates and fabricated into devices with cavity lengths ranging from 900 nm to 1800 nm. A 3-dB bandwidth of 5 GHz and 5 Gbit/s direct modulation with on-off keying were demonstrated, which were limited by the bandwidth of the photodetector used for the measurements. The differential gain of the LDs was determined to be 2.5 ± 0.5 × 10−16 cm2 by comparing the slope efficiency for different cavity lengths. Analysis of the frequency response showed that the K-factor, the gain compression factor, and the intrinsic maximum bandwidth were 0.33 ns, 7.4 × 10−17 cm3, and 27 GHz, respectively. Electronic bandstructure and optical gain of lattice matched III-V dilute nitride bismide quantum wells for 1.55 μm optical communication systems School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore and OPTIMUS, Centre for OptoElectronics and Biophotonics, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore J. Appl. Phys. http://dx.doi.org/10.1063/1.4962214

Dilute nitride bismide GaNBiAs is a potential semiconductor alloy for near- and mid-infrared

applications, particularly in 1.55 μm optical communication systems. Incorporating dilute amounts of bismuth (Bi) into GaAs reduces the effective bandgap rapidly, while significantly increasing the spin-orbit-splitting energy. Additional incorporation of dilute amounts of nitrogen (N) helps to attain lattice matching with GaAs, while providing a route for flexible bandgap tuning. Here we present a study of the electronic bandstructure and optical gain of the lattice matched GaN xBiy As1−x−yAs1−x−y/GaAs quaternary alloy quantum well (QW) based on the 16-band k ⋅· p model. We have taken into consideration the interactions between the N and Bi impurity states with the host material based on the band anticrossing and valence band anticrossing model. The optical gain calculation is based on the density matrix theory. We have considered different lattice matched GaNBiAs QW cases and studied their energy dispersion curves, optical gain spectrum, maximum optical gain, and differential gain and compared their performances based on these factors. The thickness and composition of these QWs were varied in order to keep the emission peak fixed at 1.55 μm. The well thickness has an effect on the spectral width of the gain curves. On the other hand, a variation in the injection carrier density has different effects on the maximum gain and differential gain of QWs of varying thicknesses. Among the cases studied, we found that the 6.3 nm thick GaN 3 Bi5.17Bi5.17 As91.83As91.83 lattice matched QW was most suited for 1.55 μm (0.8 eV) GaAs-based photonic applications. Green high-power tunable external-cavity GaN diode laser at 515  nm DTU Fotonik, Department of Photonics Engineering, Technical University of Danemark, Frederiksborgvej 399, P.O. Box 49, DK-4000 Roskilde, Denmark Optics Letters http://dx.doi.org/10.1364/OL.41.004154

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GANEX | Newsletter No. 45 - III-N Technology 9

A 480 mW green tunable diode laser system is demonstrated for the first time to our knowledge. The laser system is based on a GaN broad-area diode laser and Littrow external-cavity feedback. The green laser system is operated in two modes by switching the polarization direction of the laser beam incident on the grating. When the laser beam is p-polarized, an output power of 50 mW with a tunable range of 9.2 nm is achieved. When the laser beam is s-polarized, an output power of 480 mW with a tunable range of 2.1 nm is obtained. This constitutes the highest output power from a tunable green diode laser system. Proposal for a compact design for real-time optical bistability switching via a semiconductor cavity containing quantum wells Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabrz, Iran Photonics Excellence, University of Tabriz, Tabriz, Iran Applied Optics https://doi.org/10.1364/AO.55.008107

A compact design for semiconductor cavities including coupled AlGaN/AlGaAs quantum wells is proposed for all-optical switching of the bistability process. First, physical and geometrical parameters are optimized to engineer the conducting electrons’ energy levels in the quantum wells. Then, finite element simulations based on Schrödinger equations are executed to estimate the states of the charge carriers for AlGaN/AlGaAs as the active region. Next, the optical coupling and pumping fields are applied to the active region to both initiate the bistability and facilitate its real-time control. The Maxwell–Bloch approach based on rotating-wave approximation is employed to analyze the optimal conditions for controlling the behavior of optical bistability (OB). It is found that the threshold of OB can be optimized to have low values by tuning the intensity of coupling fields and the rate of an incoherent pumping field. This provides a fast real-time switching facility to control output intensity of the systems. The proposed scheme could have potential applications in optical memories, in which it is paramount to have active control over the readout of the system’s quantum states. Thanks to the high nonlinear response of

semiconductors, the featured device would be a prospective candidate for on-chip ultrasubluminal wave propagation studies and narrowband real-time switching and filtering applications. Modelling of 2-D Gallium Nitride (GaN) photonic crystal Institute of Microengineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor, Malaysia Semiconductor Electronics (ICSE), 2016 IEEE International Conference on http://dx.doi.org/10.1109/SMELEC.2016.7573589

This paper presents the simulation of a photonic crystal (PhC) cavity in low index contrast materials- Gallium Nitride on the sapphire substrate using two-dimensional (2D) Finite Difference Time Domain method (FDTD). We have performed the simulation based on H1 PhC configurations with the variation of lattice constant. We have obtained the quality factor of approximately 2200 and 1700 at the wavelength in the range of 486 and 483 nm respectively, which are suitable for operation of the blue laser. This configuration will be used as a basic building block for Lab-on-Chip (LoC) biosensors Analysis of efficiency limitations in high-power InGaN/GaN laser diodes NUSOD Institute LLC, Newark, US Optical and Quantum Electronics http://dx.doi.org/10.1007/s11082-016-0727-3

Twenty years after their first demonstration by Shuji Nakamura, InGaN/GaN lasers still exhibit less than 40 % electrical-to-optical power conversion efficiency. This paper investigates reasons behind the efficiency limitation by advanced numerical simulations of measured high-power laser characteristics. Auger recombination is identified as a major limitation at all power levels, but the inherently high series resistance becomes the most restrictive limitation at higher power. Since the traditional efficiency analysis method produces misleading results, we propose an alternative method that is also applicable without numerical simulation.

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GANEX | Newsletter No. 45 - III-N Technology 10

Phase-matched second harmonic generation with on-chip GaN-on-Si microdisks Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Bâtiment 220, Rue André Ampère, F-91405 Orsay, France CRHEA-CNRS, Rue Bernard Grégory, F-06560 Valbonne, France Scientific Reports http://dx.doi.org/10.1038/srep34191

We demonstrate phase-matched second harmonic generation in gallium nitride on silicon microdisks. The microdisks are integrated with side-coupling bus waveguides in a two-dimensional photonic circuit. The second harmonic generation is excited with a continuous wave laser in the telecom band. By fabricating a series of microdisks with diameters varying by steps of 8 nm, we obtain a tuning of the whispering gallery mode resonances for the fundamental and harmonic waves. Phase matching is obtained when both resonances are matched with modes satisfying the conservation of orbital momentum, which leads to a pronounced enhancement of frequency conversion.

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GANEX | Newsletter No. 45 - III-N Technology 11

GROUP 3 - Power Electronics Group leader: Frédéric Morancho (LAAS-CNRS)

Information selected by Frédéric Morancho (LAAS-CNRS) and Yvon Cordier (CRHEA-CNRS)

Performance enhancement of AlGaN/AlN/GaN high electron mobility transistors by thermally evaporated SiO passivation Center of Nanoelectronics and School of Microelectronics, Shandong University, Jinan 250100, China Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4962894

A surface passivation technique has been developed for AlGaN/AlN/GaN high electron mobility transistors (HEMTs) by simple thermal evaporation of silicon monoxide (SiO) at room temperature. Detailed device characteristics were studied and compared with the most commonly used SiNx passivation grown by plasma enhanced chemical vapor deposition at elevated temperatures. Both passivation techniques lead to a similar enhancement in the on-state drain current and transconductance as compared with the unpassivated HEMTs. However, we discovered that the gate leakage current in the SiO passivated devices was more than two orders of magnitude lower than the devices passivated by SiNx. Furthermore, while the SiNx passivated HEMTs exhibited a two orders of magnitude increase in off-state drain current, SiO passivation substantially reduced it, resulting in an overall improvement by a factor of 1429. The extent of the device surface damage caused by passivation was also investigated by characterizing other parameters. The subthreshold slope of the SiO passivated HEMTs was 95 mV dec−1, nearly 5 times better than the SiNx passivated devices. The extracted interface trap density was 1.16 × 1012 cm−2 eV−1, about ten times lower than that in the SiNx passivated HEMTs. Moreover, SiO passivation was found to enhance the gate Schottky barrier height by 60 meV whereas SiNx passivation reduced it, which could partially explain the differences in the gate leakage current. Finally, SiO passivation enabled twice high breakdown voltage than SiNx

passivation. The relevant physical mechanisms were discussed. Impact of Ti/Al atomic ratio on the formation mechanism of non-recessed Au-free Ohmic contacts on AlGaN/GaN heterostructures ON Semiconductor, Power Technology Centre, Corporate R&D, Westerring 15, B-9700 Oudenaarde, Belgium J. Appl. Phys. http://dx.doi.org/10.1063/1.4962314

The formation mechanism of non-recessed Au–free Ohmic contacts on the AlGaN/GaN heterostructures is investigated for various Ti/Al atomic ratios (Al–rich versus Ti–rich) and annealing temperatures ranging from 500 to 950 °C. It is shown that Ti/Al atomic ratio is the key parameter defining the optimum annealing temperature for Ohmic contact formation. Ti–rich contacts processed at high temperature result in low contact resistance ∼0.7 Ω mm, better to those obtained at low temperature or with Al–rich metal stacks. The variation of the contact resistance with Ti/Al atomic ratio and annealing temperature is correlated with the intermetallic phase changes and interfacial reaction. Depending on the Ti/Al atomic ratio, two distinct mechanisms can be distinguished. For a small quantity of Ti (e.g., Al–rich contacts), Ohmic contact formation is done through a weak interfacial reaction which is nonexistent at high temperature due to the degradation of the metal morphology. However, for a quantity of Ti higher than 25 at. % (e.g., Ti–rich contacts), the agglomeration is delayed by 200 °C as compared to Al–rich contacts, and optimal contacts are formed at high temperature through a strong interfacial reaction.

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GANEX | Newsletter No. 45 - III-N Technology 12

Correlation between mobility collapse and carbon impurities in Si-doped GaN grown by low pressure metalorganic chemical vapor deposition Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA Solid State Physics Institute, Technical University Berlin, Hardenbergstr. 36, 10623 Berlin, Germany Adroit Materials, Inc., 991 Aviation Pkwy, Suite 800, Morrisville, North Carolina 27560, USA J. Appl. Phys. http://dx.doi.org/10.1063/1.4962017

In the low doping range below 1 × 1017 cm−3, carbon was identified as the main defect attributing to the sudden reduction of the electron mobility, the electron mobility collapse, in n-type GaN grown by low pressure metalorganic chemical vapor deposition. Secondary ion mass spectroscopy has been performed in conjunction with C concentration and the thermodynamic Ga supersaturation model. By controlling the ammonia flow rate, the input partial pressure of Ga precursor, and the diluent gas within the Ga supersaturation model, the C concentration in Si-doped GaN was controllable from 6 × 1019 cm−3 to values as low as 2 × 1015 cm−3. It was found that the electron mobility collapsed as a function of free carrier concentration, once the Si concentration closely approached the C concentration. Lowering the C concentration to the order of 1015 cm−3 by optimizing Ga supersaturation achieved controllable free carrier concentrations down to 5 × 1015 cm−3 with a peak electron mobility of 820 cm2/V s without observing the mobility collapse. The highest electron mobility of 1170 cm2/V s was obtained even in metalorganic vapor deposition-grown GaN on sapphire substrates by optimizing growth parameters in terms of Ga supersaturation to reduce the C concentration.

Electrical characterization of a gate-recessed AlGaN/GaN high-electron-mobility transistor with a p-GaN passivation layer Department of Digital Multimedia Technology, Vanung University, Chung-Li, 32061, Taiwan J. Vac. Sci. Technol. B http://dx.doi.org/10.1116/1.4963897

A novel passivation technique was developed that reduces the electron-surface-hopping-induced leakage current of AlGaN/GaN high-electron-mobility transistors (HEMTs) and enhances their electrical properties under high drain bias operation. The key aspect of this passivation technique entailed growing a p-type GaN layer on a traditional depletion-mode AlGaN/GaN HEMT; this p-GaN passivation layer was also used as the spacer layer of a field-plate metal. The originally exposed gate-to-source and gate-to-drain areas were passivated by the p-GaN cap layer. Thus, a surface depletion region was formed between the p-GaN passivation layer and an n-type AlGaN/GaN two-dimensional electron gas channel. This extra surface depletion region depleted the channel carriers far from the surface to reduce the probability of the carriers being trapped by surface defects. Therefore, the carrier-hopping-induced leakage current in the gate-to-drain area, which was strongly temperature-dependent, was suppressed. Low-frequency noise (LFN) measurement revealed that the traditional chemical-vapor-deposited SiO2 layer still exhibited a surface trap center. Moreover, the slope of a plot of noise spectra versus gate overdrive voltage was approximately −3. At a cryogenic temperature, the LFN of the p-GaN—passivated device improved by 3 orders of magnitude, whereas the high surface trap density of the standard passivated device resulted in a high LFN, even at a cryogenic temperature.

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GANEX | Newsletter No. 45 - III-N Technology 13

AlGaN channel field effect transistors with graded heterostructure ohmic contacts Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4963860

We report on ultra-wide bandgap (UWBG) Al 0.75Ga0.25N channel metal-insulator-semiconductor field-effect transistors (MISFETs) with heterostructure engineered low-resistance ohmic contacts. The low intrinsic electron affinity of AlN (0.6 eV) leads to large Schottky barriers at the metal-AlGaN interface, resulting in highly resistive ohmic contacts. In this work, we use a reverse compositional graded n++ AlGaN contact layer to achieve upward electron affinity grading, leading to a low specific contact resistance (ρsp) of 1.9 × 10−6 Ω cm2 to n-Al0.75Ga0.25N channels (bandgap ∼5.3 eV) with non-alloyed contacts. We also demonstrate UWBG Al 0.75Ga0.25N channel MISFET device operation employing the compositional graded n++ ohmic contact layer and 20 nm atomic layer deposited Al 2O3 as the gate-dielectric. Structural properties and transfer characteristics of sputter deposition AlN and atomic layer deposition Al2O3 bilayer gate materials for H-terminated diamond field effect transistors Optical and Electronic Materials Unit, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan J. Appl. Phys. http://dx.doi.org/10.1063/1.4962854

Significant improvements in electrical properties are achieved from AlN/Al2O3 stack gate H-terminated diamond metal-insulator-semiconductor field-effect transistors (MISFETs) upon improving the structural quality of an AlN insulating layer. The 5-nm-thick Al2O3 layer and 175-nm-thick AlN film are successively deposited by atomic layer deposition and sputter deposition techniques, respectively, on a (100) H-diamond epitaxial layer substrate. The AlN layer exhibits a poly-crystalline structure with the hexagonal wurtzite phase. The crystallite growth proceeds along the c-axis direction and perpendicular to the

substrate surface, resulting in a columnar grain structure with an average grain size of around ∼40 nm. The MIS diode fabricated provides a leak current density as low as ∼10−5 A/cm2 at gate voltage bias in the range of −8 V and +4 V. The MISFET fabricated shows normally off enhancement mode transfer characteristic. The drain-source current maximum, threshold voltage, and maximum extrinsic conductance of the FET with 4 μm gate length are −8.89 mA/mm, −0.22 V, and 6.83 mS/mm, respectively. Degradation Characteristics of Normally-off p-AlGaN gate AlGaN/GaN HEMTs with 5 MeV Proton Irradiation School of Electronics and Electrical Engineering, Hongik University, Seoul, Korea IEEE Transactions on Nuclear Science http://dx.doi.org/10.1109/TNS.2016.2612227

Proton irradiation at 5 MeV was performed on normally-off p-AlGaN gate AlGaN/GaN high electron mobility transistors (HEMTs). The increase of on-resistance and the degradation of subthreshold characteristics were observed after irradiation. The reduction of on-current was induced by displacement damage which also affected ungated devices with no p-AlGaN gate layer. Thermal annealing partially recovered this reduction. The subthreshold degradation with the threshold voltage (Vth) shift was proportional to the irradiation dose. TCAD simulation indicated that the decrease of hole concentration in p-AlGaN layer resulted in the negative shift of Vth and the subthreshold degradation. Unique ESD behavior and failure modes of AlGaN/GaN HEMTs Advance Nanoelectronic Device and Circuit Research Laboratory, Department of Electronic Systems Engineering, Indian Institute of Science, Bangalore 560012, India Reliability Physics Symposium (IRPS), 2016 IEEE International http://dx.doi.org/10.1109/IRPS.2016.7574608

Present experimental study reports various failure modes under ESD stress conditions and distinct ESD behavior of AlGaN/GaN HEMTs for the first

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time. Effect of MESA isolation and gate finger on the ESD behavior of HEMTs is analyzed. Effect of pulse width on ESD robustness and snapback voltage is observed and a unique power law like behavior is found. Cumulative nature of device degradation under ESD stress condition is discovered. Correlation between depth of snapback and failure threshold with % device degradation is found. Finally, impact of inverse piezoelectric effect in AlGaN/GaN system, fringing electric field, role of contact resistivity, temperature and field induced contact metal migration and premature breakdown of parasitic MESA Schottky junction are studied in context to AlGaN/GaN HEMT failure ESD conditions. On conduction mechanisms through SiN/AlGaN based gate dielectric and assessment of intrinsic reliability ON Semiconductor, Westerring 15, 9700 Oudenaarde, Belgium Reliability Physics Symposium (IRPS), 2016 IEEE International http://dx.doi.org/10.1109/IRPS.2016.7574585

The first section of this article focuses on the investigations of the gate leakage conduction mechanisms under forward and reverse bias conditions using temperature dependent Jg-Eg characteristics on a Silicon Nitride (SiN)/AlGaN based Metal-Insulator-Semiconductor (MIS) structure. TCAD study under forward bias conduction show majority of the voltage drop on the SiN layer only. The model fitting the electrical characteristics was observed to be Poole-Frenkel (PF) emission. Under reverse bias condition, the entire voltage drop occurs on the entire SiN/AlGaN/GaN. The conduction mechanism responsible for the leakage was found to be Fowler-Nordheim (FN) tunneling along with a thermionic emission component. Second section of this article focuses on the Time Dependent Dielectric Breakdown (TDDB) measurements and lifetime extrapolation of the SiN/AlGaN based di-electric stack. TDDB measurements were done under constant field stress for different temperatures. Normalization of the data exhibited only field accelerated degradation with no influence from the temperature.

Device breakdown optimization of AhOs/GaN MISFETs imec, Leuven, Belgium Reliability Physics Symposium (IRPS), 2016 IEEE International http://dx.doi.org/10.1109/IRPS.2016.7574589

In this paper we demonstrate a solution to achieve robust enhancement-mode Al2O3/GaN MISFETs with a high breakdown voltage and suggest a possible model for the device off-state breakdown. It is found that the device breakdown exhibits different gate voltage dependence for different surface treatments before the gate dielectric deposition. The device performance is greatly improved by using an in-situ surface plasma treatment. The improved device performance is explained by a reduction of traps at the Al2O3/GaN interface, which finally leads to a reduction in the amount of trapped positive charges and associated with that a reduction of the effective electric field across the gate dielectric when the device is in off-state. Several experimental results support this hypothesis: (1) The recoverable negative threshold voltage shift after reverse gate bias depends on the interface clean before gate dielectric deposition, (2) The reverse bias gate dielectric breakdown voltage is improved by this interface plasma treatment, although the forward bias gate dielectric breakdown voltage is identical. Design and manufacturability of a high power density M2C inverter Department of Electrical and Computer Engineering, University of Pittsburgh, PA; USA 3D Power Electronics Integration and Manufacturing (3D-PEIM), International Symposium on http://dx.doi.org/10.1109/3DPEIM.2016.7570559

The modular multilevel converter (M2C) circuit, a voltage source converter originally introduced to reduce the footprint of high voltage DC systems, is adapted here for a single-phase, low voltage, high power density inverter application (450 VDC, 2 kW, 100 W/in3). The adaptation is achieved by using small, high speed gallium nitride (GaN) transistors in the M2C half-bridge submodules that are stacked in series and parallel to achieve

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voltage and current requirements. Here the design and analysis of an individual half-bridge cell, and full arm of the M2C topology is presented. To achieve such high power density, factors including gate drive circuit design, submodule electrical performance and thermal management, and the manufacturability of the full arm were considered. This work presents the detailed process of designing and manufacturing the multiple printed circuit boards, as well as thermal and electrical experimental evaluation and analysis. The stringent size and operational requirements drove design iterations between circuit designers and manufacturers. Correlation between dynamic Rdson transients and Carbon related buffer traps in AlGaN/GaN HEMTs STMicroelectronics, Stradale Primosole 50, 95121 Catania, Italy Reliability Physics Symposium (IRPS), 2016 IEEE International http://dx.doi.org/10.1109/IRPS.2016.7574586

The on resistance increment observed when the device is operated at high drain-source voltages is one the topics that limits the performance of the AlGaN/GaN HEMT devices. In this paper, the physical mechanisms responsible of the RDSon degradation are investigated. The dynamic RDSon transient method is used in order to get insight to characterize the traps states. By calculating the Arrhenius plot associated with the RDSon transients an activation energy of 0.86eV was extracted, that can be correlated to the traps due to the incorporation of Carbon inside the buffer. This hypothesis was further supported by the analyses performed on a simpler structure (TLM). By applying a negative substrate bias the effect of only the buffer traps was studied. A fairly close value of the activation energy (0.9eV) to the one extracted when analyzing the RDSon transient was obtained.

Positive bias temperature instability evaluation in fully recessed gate GaN MIS-FETs imec, Leuven, Belgium Reliability Physics Symposium (IRPS), 2016 IEEE International http://dx.doi.org/10.1109/IRPS.2016.7574527

In this paper, positive bias temperature instability (PBTI) in fully recessed gate GaN MIS-FETs is studied by using an eMSM (extended Measure-Stress-Measure) technique, which consists of a set of stress/recovery tests. By using this technique, VTH shift after a stress and the relaxation information can be collected in one experiment. First of all, a typical forward-reverse gate sweep and frequency-dependent conductance method are used to characterize VTH shift and interface state density (Dit) in fully recessed gate MIS-FETs with two different gate dielectrics (PEALD SiN and ALD AhO3), showing that ALD AhO3 has a smaller VTH shift compared with PEALD SiN although the latter has a smaller Dit. Then, an eMSM technique is used to understand the trapping/de-trapping phenomena under stress and relaxation period. The results show a power law dependency of VTH shift with respect to the stress time. Furthermore, the voltage dependency of Vth shift (7) can be extracted, showing that ALD Al2O3 has a higher 7 compared to PEALD SiN. The physical model is proposed to explain the mechanism for the different voltage dependency. On the other hand, the relaxation data is collected as well, indicating that Al2O3 has a faster relaxation even under a high voltage overdrive stress, which is consistent with physical model since accessibility of defects in Al2O3 are located at energies less favorable for channel carriers, compared to SiN. Investigation of trapping effects on AlGaN/GaN HEMT under DC accelerated life testing Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH 43210, USA Reliability Physics Symposium (IRPS), 2016 IEEE International http://dx.doi.org/10.1109/IRPS.2016.7574587

GaN-based high electron mobility transistors (HEMTs) were subjected to DC-based accelerated life testing to determine which defect levels form

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or are activated, and how they impact the static and dynamic HEMT performance. The primary static changes were a negative shift of the threshold voltage and an increase in knee walkout/on-resistance. The primary dynamic effect of the stressing appeared in the form of a time-dependent increase in the on-resistance, and this was found to correlate to first order with formation and/or activation of traps at Ec-0.57 and Ec-0.72 eV traps that contributed to the dynamic changes, and the Ec-1.5 eV trap was likely responsible for the static change in on-resistance. Trapping kinetics analysis revealed that the physical sources for the EC-0.57 and EC-0.72 eV states are not simple, ideal, non-interacting point defects, but instead are associated with physically extended defects, such as dislocations, and/or defect complexes. A fully integrated GaN-based power IC including gate drivers for high-efficiency DC-DC Converters Engineering Division, Automotive & Industrial Systems Company, Panasonic Corporation, Nagaokakyo-shi, Kyoto, Japan VLSI Circuits (VLSI-Circuits), 2016 IEEE Symposium on http://dx.doi.org/10.1109/VLSIC.2016.7573496

In this paper, we present a state-of-the-art integrated GaN power IC capable of operating in a high frequency (MHz) regime. This realizes system size reduction, 60% maximum, of a power IC. The IC consists of two output power transistors (PT) and two gate drivers (GD). The key devices in the IC are normally-off gate injection transistors (GITs) for PT and GD and a normally-on hetero-junction field effect transistor (HFET) for GD. Novel local control of carrier concentration of an identical 2 dimensional electron gas (2DEG) at an AlGaN/GaN interface which made integration of the transistors with such a large threshold voltage difference possible is described. A specially developed post-passivation interconnection process giving low parasitic components is also described. The IC applied to a 12V–1.8V DC-DC converter shows high frequency switching operation well beyond the limit of Si pointing to future improvement in consumer electronics power supply systems.

Impact of buffer charge on the reliability of carbon doped AlGaN/GaN-on-Si HEMTs Center for Device Thermography and Reliability, University of Bristol, Bristol BS8 1TL, UK Reliability Physics Symposium (IRPS), 2016 IEEE International http://dx.doi.org/10.1109/IRPS.2016.7574529

Charge trapping and transport in the carbon doped GaN buffer of an AlGaN/GaN-on-Si high electron mobility transistor (HEMT) have been investigated. Back-gating and dynamic Ron experiments show that a high vertical leakage current results in significant long-term negative charge trapping in the buffer leading to current collapse under standard device operating conditions. Controlling current-collapse requires control of not only the layer structures and its doping, but also the precise balance of leakage in each layer. Understanding the degradation sources under ON-state stress in AlGaN/GaN-on-Si SBD: Investigation of the anode-cathode spacing length dependence ARCES, DEI-“Guglielmo Marconi”, University of Bologna, Cesena, Italy Reliability Physics Symposium (IRPS), 2016 IEEE International http://dx.doi.org/10.1109/IRPS.2016.7574530

In this paper, we report an analysis of the degradation induced by ON-state stress in Au-free AlGaN/GaN-on-Si Schottky barrier diodes (SBDs). When the device operates in ON-state mode, the combined effect of large currents and moderate electric fields may cause a shift of the turn-on voltage (VTON) and ON-resistance (RON) because of the charge carrier trapping/de-trapping, occurring in different regions and related to different types of defects. In particular, the influence of the anode-cathode spacing length on the ON-state degradation has been investigated and the degradation sources, attributable to ΔVTON and ΔRON, have been understood. Moreover, thanks to this approach, a critical electric field for the RON degradation has been reported.

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Dynamic Modeling and Power Loss Analysis of High-Frequency Power Switches Based on GaN CAVET School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ, USA IEEE Transactions on Electron Devices http://dx.doi.org/10.1109/TED.2016.2601559

The focus of this paper is to understand the impact of the material properties of GaN, exploited using a vertical device, in power switching by estimating switching loss. The study was performed with a cascoded current aperture vertical electron transistor (CAVET). The normally OFF device was simulated and analyzed using a Silvaco ATLAS 2-D drift diffusion model integrated to SPICE-based circuit simulator. Besides evaluating the performance space and, hence, potential application space for GaN CAVETs, this paper presents significant accomplishment in establishing a device to circuit model, thereby, offering a reliable method of evaluating GaN-based power transistors. The accuracy of the model was established through the excellent agreement of simulated data with the data sheet specs of a commercial cascoded GaN high electron mobility transistor. The model was successfully applied to compare SiC MOSFETs with GaN CAVETs. A cascoded GaN CAVET has 2× faster switching time, 3× lower switching loss compared with standard commercial SiC MOSFET, owing to the higher electron mobility in GaN. Operating at frequencies of megahertz with low power loss, a GaN CAVET will, therefore, lead to smaller converter size and higher system efficiency. Physics of GaN High Electron Mobility Transistors Rensselaer Polytechnic Institute ECS Trans. http://dx.doi.org/10.1149/07512.0069ecst

The nitride High Electron Mobility (HEMTs) have a great potential for high power and RF applications because of a high breakdown field, a very large density of the polarization induced two-dimensional electrons, high electron velocities and mobilities, excellent thermal properties, chemical inertness, and radiation hardness. GaN power transistors grown on silicon substrates are

already being commercialized. However, the full potential of the nitride based HEMTs is still to be achieved and will require improvements in the device design that account for the both materials properties and device physics of wide band gap transistors. Such new features include the diamond substrates for a better heat removal, adding a low conducting passivation between the gate and drain, using the perforated channel with perforations extending beyond the gate, implementing the HEMT technology in the AlInN/GaN materials system for lattice matching design and employing lateral-vertical designs for a higher breakdown voltage. Carbon-Doped GaN on SiC Materials for Low-Memory-Effect Devices SweGaN AB Linköping University Chalmers University ECS Trans. http://dx.doi.org/10.1149/07512.0061ecst

AlGaN/GaN on SiC HEMT structures suitable for high power, high frequency applications are demonstrated. The material manifests record breaking thermal management and electron mobility. Moreover, thanks to the fact that the buffer layer is doped with carbon, the memory effect of processed devices is very low making system design and manufacturing significantly easier and less expensive. Strain Engineered Crack-Free GaN on Si for Integrated Vertical High Power GaN Devices with Si CMOS UC San Diego ECS Trans. http://dx.doi.org/10.1149/07508.0711ecst

The ability to grow thin GaN layers on Si substrates has led to the development of lateral high power and high-speed devices such as GaN HEMTs. These devices have already demonstrated promising performance and have been adopted for mass market. But lateral devices require large drain/gate separation to sustain high voltage impairing cost effectiveness. This highlights the need for growth of thick GaN layers to enable

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vertical high power device architectures and to achieve high performance and attain high breakdown voltages in small chip area. This paper presents a successful growth of over 10μm thick crack-free GaN on Si by engineering the strain induced by thermal mismatch between GaN and Si. We discuss the origin of cracking and introduce a surface strain-relief mechanism in 0.5mm diameter GaN dots to overcome thermal mismatches. The first demonstration of vertical thick GaN Schottky diodes on Si will be presented. To fully exploit these results of GaN power devices on Si, side-by-side integration of GaN and CMOS circuitry elements is necessary. We have assessed and validated the compatibility of the GaN-CMOS process. These advances can pave the way for commercialization of next generation compact and efficient power systems that are composed of monolithically integrated GaN and Si technologies. Effect of nitrogen incorporation into Al-based gate insulators in AlON/AlGaN/GaN metal–oxide–semiconductor structures Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan Panasonic Corporation, Nagaokakyo, Kyoto 617-8520, Japan Japan Atomic Energy Agency, Sayo, Hyogo 679-5148, Japan Applied Physics Express http://dx.doi.org/10.7567/APEX.9.101002

The superior physical and electrical properties of aluminum oxynitride (AlON) gate dielectrics on AlGaN/GaN substrates in terms of thermal stability, reliability, and interface quality were demonstrated by direct AlON deposition and subsequent annealing. Nitrogen incorporation into alumina was proven to be beneficial both for suppressing intermixing at the insulator/AlGaN interface and reducing the number of electrical defects in Al2O3 films. Consequently, we achieved high-quality AlON/AlGaN/GaN metal–oxide–semiconductor capacitors with improved stability against charge injection and a reduced interface state density as low as 1.2 × 1011 cm−2 eV−1. The impact of nitrogen incorporation into the insulator will be discussed on the basis of experimental findings.

Insulated gate and surface passivation structures for GaN-based power transistors Priority Organization for Innovation and Excellence, Kumamoto University, Kumamoto 860-8555, Japan Graduate School of Engineering, University of Fukui, Fukui 910-8507, Japan Research Center for Integrated Quantum Electronics (RCIQE), Hokkaido University, Sapporo 060-0814, Japan Journal of Physics D: Applied Physics http://dx.doi.org/10.1088/0022-3727/49/39/393001

Recent years have witnessed GaN-based devices delivering their promise of unprecedented power and frequency levels and demonstrating their capability as an able replacement for Si-based devices. High-electron-mobility transistors (HEMTs), a key representative architecture of GaN-based devices, are well-suited for high-power and high frequency device applications, owing to highly desirable III-nitride physical properties. However, these devices are still hounded by issues not previously encountered in their more established Si- and GaAs-based devices counterparts. Metal–insulator–semiconductor (MIS) structures are usually employed with varying degrees of success in sidestepping the major problematic issues such as excessive leakage current and current instability. While different insulator materials have been applied to GaN-based transistors, the properties of insulator/III-N interfaces are still not fully understood. This is mainly due to the difficulty of characterizing insulator/AlGaN interfaces in a MIS HEMT because of the two resulting interfaces: insulator/AlGaN and AlGaN/GaN, making the potential modulation rather complicated. Although there have been many reports of low interface-trap densities in HEMT MIS capacitors, several papers have incorrectly evaluated their capacitance–voltage (C–V) characteristics. A HEMT MIS structure typically shows a 2-step C–V behavior. However, several groups reported C–V curves without the characteristic step at the forward bias regime, which is likely to the high-density states at the insulator/AlGaN interface impeding the potential control of the AlGaN surface by the gate bias. In this review paper, first we describe critical issues and problems including leakage current, current collapse and threshold voltage instability in AlGaN/GaN HEMTs. Then we

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present interface properties, focusing on interface states, of GaN MIS systems using oxides, nitrides and high-κ dielectrics. Next, the properties of a variety of AlGaN/GaN MIS structures as well as different characterization methods, including our own photo-assisted C–V technique, essential for understanding and developing successful surface passivation and interface control schemes, are given in the subsequent section. Finally we highlight the important progress in GaN MIS interfaces that have recently pushed the frontier of nitride-based device technology.

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GROUP 4 - Advanced Electronics and RF Group leader: Jean-Claude Dejaeger (IEMN)

Information selected by Jean-Claude Dejaeger (IEMN) and Yvon Cordier (CRHEA-CNRS)

Model to explain the behavior of 2DEG mobility with respect to charge density in N-polar and Ga-polar AlGaN-GaN heterostructures Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106, USA J. Appl. Phys. http://dx.doi.org/10.1063/1.4962321

There are three possible ways of reducing the charge density (ns) in the N-polar high electron mobility transistors (HEMT) structures, by decreasing the channel thickness, applying reverse gate bias, or modifying the back-barrier. Understanding the behavior of 2DEG mobility as a function of ns is essential to design high performance HEMT devices. Experimental data show that in the N-polar HEMT structures, the 2DEG mobility reduces as the ns decreases by applying reverse gate bias or decreasing channel thickness, whereas in the Ga-polar HEMT structures, the 2DEG mobility increases as the ns in the channel decreases by applying reverse gate bias. In this paper, the 2DEG mobility as a function of ns is calculated in N-polar HEMTs for three different aforementioned cases, and is compared to that in the Ga-polar HEMT structures. It is shown that the conventional scattering mechanisms cannot explain these different behaviors. Two new scattering mechanisms, such as scattering from charged interface states and surface state dipoles (SSD), are introduced. It is revealed that in N-polar HEMT structures, reducing ns by applying reverse gate bias or decreasing channel thickness moves the charge centroid closer to the AlGaN-GaN interface. A combination of lower charge density (less screening of the scattering potential) and smaller distance between charge centroid and charged states at the interface leads to a severe mobility degradation in these cases. In contrast, reducing ns by modifying the back-barrier (decreasing back-barrier doping and/or decreasing AlGaN composition) in N-polar HEMT structures moves the charge centroid away from the interface. This

behavior is similar to that in the Ga-polar HEMT structures. Therefore, in the last two mentioned cases, the 2DEG mobility first increases slightly as the ns decreases, and decreases slightly at very low charge densities. It is also shown that SSDs have large impact on the 2DEG mobility only in the N-polar (Ga-polar) HEMTs with thin channels (barriers). Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611 Department of Materials Science Engineering, University of Florida, Gainesville, Florida 32611 J. Vac. Sci. Technol. B http://dx.doi.org/10.1116/1.4963064

AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffer layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm−2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.

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A class-F 5 – 6 GHz 10-W GaN-on-SiC amplifier Kim Tran Wireless and Microwave Circuits and Systems (WMCS), 2016 Texas Symposium on http://dx.doi.org/10.1109/WMCaS.2016.7577496

A Class-F 5 – 6 GHz 10 W Power Amplifier was designed with Qorvo's T2G6000528-Q3 GaN transistor using a model developed by Modelithics™. The core of this device is a 10-W die constructed with Qorvo's proven QGaN25 production process that is optimized for high power density and drain efficiency. The optimization design process involves producing model load-pull contours to identify area of loading termination for optimal power and efficiency, and simultaneously proper second-harmonic termination for high-efficiency. 5 amplifiers were built and tested. Test results showed excellent 3dB-compression performance with drain efficiency ranging from 60 to 79.5% and power above 10 W. Microwave Low-Noise Performance of 0.17 μm Gate-Length AlGaN/GaN HEMTs on SiC with Wide Head Double-Deck T-Shaped Gate IT Components and Materials Research Laboratory, Electronics and Telecommunications Research Institute, 218 Gajeong-ro, Yuseong-gu, Daejeon 34129, Republic of Korea IEEE Electron Device Letters http://dx.doi.org/10.1109/LED.2016.2612624

Microwave low-noise performance AlGaN/GaN HEMT on a SiC substrate with a wide head double-deck T-shaped gate has been reported. The HEMTs with gate-length ( Lg ) of 0.17 μ m and source-drain spacing ( Lsd ) of 3.5 μ m exhibited a maximum extrinsic transconductance of 360 mS/mm, a current gain cutoff frequency ( fT ) of 50 GHz, a maximum oscillation frequency ( fmax ) of 149 GHz, and three-terminal BV of 113 V. The device exhibited a minimum noise figure ( NFmin ) of 0.50 and 0.84 dB at 10 and 18 GHz, respectively, when biased at Vds = 5 V and Ids = 140 mA/mm, which is the lowest noise characteristics ever reported for the GaN-based T-shaped gate HEMTs with gate length larger than 0.1 μ m. This excellent noise performance is

attributed to the reduction of the gate resistance resulting from a wide head T-shaped gate and the improved device characteristics. W-Band MMIC PA With Ultrahigh Power Density in 100-nm AlGaN/GaN Technology Nanjing Electronic Devices Institute, Nanjing, China IEEE Transactions on Electron Devices http://dx.doi.org/10.1109/TED.2016.2597244

A three-stage W-band GaN monolithic microwave integrated circuit power amplifier (MMIC PA) is reported. Electron-beam lithography has been employed to define a 100-nm T-shaped gate on the AlGaN/GaN HEMT structure with ultrahigh aluminum content. The MMIC PA offers a peak small signal gain of 16.7 dB in the 90–97 GHz bandwidth. Moreover, it achieves a peak 1.66-W (32.2 dBm) output power at 93 GHz in a continuous-wave mode, with an associated power added efficiency of 21% and an associated power gain of 13.7 dB. Most notably, the peak power density is 3.46 W/mm with a 480- μm wide output stage, which exceeds 3 W/mm in AlGaN/GaN HEMT at W-band for the first time. GaN High-Electron Mobility Transistor Track-and-Hold Sampling Circuit With Over 100-dB Signal-to-Noise Ratio Analog Devices, Wilmington, MA, USA IEEE Electron Device Letters http://dx.doi.org/10.1109/LED.2016.2598806

A track-and-hold sampling circuit (THSC) fabricated in gallium nitride (GaN) high-electron mobility transistor (HEMT) on silicon carbide substrate is presented for the first time, considering the impact of GaN HEMT memory effects on the sampled signal. A single-transistor GaN track-and-hold sampler with an external gate-bootstrapping sampling clock demonstrates over 100-dB signal-to-noise ratio with 700-MHz track-mode bandwidth.

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AlGaN/GaN HEMTs on Silicon With Hybrid Schottky-Ohmic Drain for RF Applications Electrical Engineering Department, National Tsing Hua University, Hsinchu 30013, Taiwan. IEEE Transactions on Electron Devices http://dx.doi.org/10.1109/TED.2016.2605128

In this paper, the AlGaN/GaN high electron mobility transistors on a low resistivity Si substrate with the hybrid drain structure for RF applications are analyzed in detail, based on measurements, TCAD simulation, model extraction, and delay time calculation of the transistors. Owing to the E-field redistribution of the Schottky extension, both the leakage current and the breakdown voltage can be improved. Also, the enhanced RF performance can be attributed to the reduced transit time and increased transconductance, resulting from the increased electron velocity and reduced drain depletion width. With a 3-μm extension length and a 0.2-μm gate length, fT and fMAX$ of transistors can be improved from 32.7 to 49.9 GHz (52.6%) and from 35.8 to 49.2 GHz (37.4%), respectively, with ON-OFF ratio enhancement by four orders of magnitude. The breakdown voltage was improved from 21 to 38 V (80.9%). RF Performance of Trigate GaN HEMTs Fachgebiet Festkörperelektronik, Technische Universität Ilmenau, 98684 Ilmenau, Germany IEEE Transactions on Electron Devices http://dx.doi.org/10.1109/TED.2016.2606701

The impact of the trigate GaN high electron mobility transistor (HEMT) body geometry on the device RF performance is investigated by 3-D numerical simulations. The trigate concept is a viable approach to achieve normally off operation and to suppress short-channel effects. The effect of gate length scaling on the RF behavior is studied and guidelines for design improvements are provided. Furthermore, it is shown that trigate HEMTs with improved body design and/or InAlN barriers causing a higher polarization charge than AlGaN can exhibit better RF figures of merit than planar GaN HEMTs.

RF Power Performance of Nanocrystalline Diamond Coated InAlN/AlN/GaN HEMTs U.S. Naval Research Laboratory ECS Trans. http://dx.doi.org/10.1149/07512.0085ecst

We have previously demonstrated AlGaN/GaN high-electron-mobility transistors (HEMTs) that used a coating of high thermal conductivity nanocrystalline diamond (NCD) to reduce channel temperature for a given dissipated power and simultaneously improve electrical performance compared to devices with conventional silicon nitride (SiN) passivation only. Here we examine the effect of a protective SiN interlayer of varying thickness inserted between the semiconductor surface and NCD coating on large-signal output power density as well as the reduction in channel temperature. For an InAlN/AlN/GaN HEMT with a >1 µm NCD coating and SiN interlayer ranging from 5 to 50 nm in thickness, the output power density and power-added efficiency at 4 and 10 GHz are found to be maximized for the thickest SiN interlayer. At the same time, we find the reduction in channel temperature provided by the NCD coating is not strongly dependent on thickness, which is confirmed by numerical simulation. Manufacturing Microwave AlGaN/GaN High Electron Mobility Transistors (HEMTs) on Truly Bulk Semi-Insulating GaN Substrates Institute of Electron Technology, Warsaw, Poland Institute of Radioelectronics, WUT, Warsaw, Poland Ammono S.A. Institute of High Pressure Physics, PAS, Warsaw, Poland TopGaN Ltd., Warsaw, Poland Inst. of Micro- and Optoelectronics, WUT, Warsaw, Poland ECS Trans. http://dx.doi.org/10.1149/07512.0077ecst

The substrate of choice for high power microwave GaN-based devices is silicon carbide. However recently novel semi-insulating truly bulk GaN substrates with excellent crystalline and electrical parameters have been developed by Ammono S..A. These allow to elaborate AlGaN/GaN heterostructures with high electron mobility

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values and density of two-dimensional electron gas. Developed processing steps, especially planar isolation by ion implantation and formation of low resistivity regrown ohmic contacts enabled fabrication of high quality devices. An 1000 mA/mm on-state current density along with low 4.4 Ω/mm on-state resistance were achieved. For the devices with rectangular, 0.8 μm gate length the fMAG and fs were 31 GHz and 22 GHz. The maximum output power density was more than 4.15 W/mm in S-band.

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GANEX | Newsletter No. 45 - III-N Technology 24

GROUP 5 – MEMS and Sensors Group leader: Marc Faucher (IEMN) Information selected by Knowmade

Growth of hexagonal boron nitride on (111) Si for deep UV photonics and thermal neutron detection Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4962831

Hexagonal boron nitride (hBN) growth was carried out on (111) Si substrates at a temperature of 1350 °C using a cold wall chemical vapor deposition system. The hBN phase of the deposited films was identified by the characteristic Raman peak at 1370 cm−1 with a full width at half maximum of 25 cm−1, corresponding to the in-plane stretch of B and N atoms. Chemical bonding states and composition of the hBN films were analyzed by X-ray photoelectron spectroscopy; the extracted B/N ratio was 1.03:1, which is 1:1 within the experimental error. The fabricated metal-hBN-metal devices demonstrate a strong deep UV (DUV) response. Further, the hBN growth on the vertical (111) surfaces of parallel trenches fabricated in (110) Si was explored to achieve a thermal neutron detector. These results demonstrate that hBN-based detectors represent a promising approach towards the development of DUV photodetectors and efficient solid-state thermal neutron detectors. A microfabricated sun sensor using GaN-on-sapphire ultraviolet photodetector arrays Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305, USA Rev. Sci. Instrum. http://dx.doi.org/10.1063/1.4962704

A miniature sensor for detecting the orientation of incident ultraviolet light was microfabricated using gallium nitride (GaN)-on-sapphire substrates and semi-transparent interdigitated gold electrodes for sun sensing applications. The

individual metal-semiconductor-metal photodetector elements were shown to have a stable and repeatable response with a high sensitivity (photocurrent-to-dark current ratio (PDCR) = 2.4 at −1 V bias) and a high responsivity (3200 A/W at −1 V bias) under ultraviolet (365 nm) illumination. The 3 × 3 GaN-on-sapphire ultraviolet photodetector array was integrated with a gold aperture to realize a miniature sun sensor (1.35 mm × 1.35 mm) capable of determining incident light angles with a ±45° field of view. Using a simple comparative figure of merit algorithm, measurement of incident light angles of 0° and 45° was quantitatively and qualitatively (visually) demonstrated by the sun sensor, supporting the use of GaN-based sun sensors for orientation, navigation, and tracking of the sun within the harsh environment of space. Effect of III-V nitrides on performance of graphene based SPR biosensor for detection of hemoglobin in human blood sample: A comparative analysis Department of Physics, National Institute of Technology Raipur, C.G 492010, India Current Applied Physics http://dx.doi.org/10.1016/j.cap.2016.09.006

In the quest for the development of highly sensitive and accurate optical biosensor for the detection of hemoglobin (Hb) concentration, theoretically we have investigated the effect of iii-v nitride on performance of graphene based SPR biosensor. To achieve the performance, computation has been performed for single metal and bi-metal individually for graphene based SPR configuration. Due to the addition of iii-v nitride layer in between metal and graphene layer in the proposed configuration, the overall sensitivity is enhanced and also detects very small volume of Hb. Finally, a comparative analysis has been carried out to establish that nearly 3:1 ratio bi-metallic combination (i.e. Ag38Au12) based SPR sensor can demonstrate better response.

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GANEX | Newsletter No. 45 - III-N Technology 25

Additionally, introduction of indium nitride (InN) is more beneficial in comparison to other semiconductors. We expect that this study will motivate the researchers in the fabrication industry and helps physician to analyze Hb in real time. Optimization of GaN-Based HEMTs for Chemical Sensing: A Simulation Study University of Florida ECS Trans. http://dx.doi.org/10.1149/07516.0259ecst

Understanding the influence of device parameters on optimization of GaN-based High-Electron-Mobility Transistors (HEMT)s is crucial for development of effective and power-efficient sensors. This research provides a simulation study that shows trends for optimum sensor performance with regard to drain bias and gate length. TCAD simulations model a pH sensor as a general example. GaN MISIM Diode with High-k Dielectrics of ZrO2 and Al2O3 for UV Sensing Kyungpook National University, South Korea ECS Trans. http://dx.doi.org/10.1149/07511.0053ecst

We fabricated a GaN MISIM (metal-insulator-semiconductor-insulator-metal) UV photodiode using two high-k dielectrics of ZrO2 and Al2O3. The fabricated UV photodiode using ZrO2 showed better photo-electronic properties than that using Al2O3. The dark and photo-responsive current density ratios of the device with ZrO2 and Al2O3 were 250 and 196 at 10 V bias. Their UV/visible rejection ratios (UVRRs) were 1.65 × 102 and 1.34 × 102 for 365 nm wavelength at 1 V bias, respectively. The noise spectral density of the device with ZrO2 was 1.3 × 102 A2/Hz for 10 Hz at 3 V bias which has lower noise value than that with Al2O3. The GaN MISIM UV photodiode with ZrO2 has over 20 % improved photo-electronic properties and lower noise than that with Al2O3.

Piezoelectric MEMS resonators based on ultrathin epitaxial GaN heterostructures on Si CRHEA-CNRS, UPR10, rue Bernard Grégory, 06560 Valbonne, France IEMN, CNRS UMR 8520, Avenue Poincaré, CS 60069, 59652 Villeneuve d'Ascq Cedex, France Journal of Micromechanics and Microengineering http://dx.doi.org/10.1088/0960-1317/26/10/105015

We present the first results for microelectromechanical (MEMS) resonators fabricated on epitaxial nitride semiconductors with thin buffers engineered for MEMS and NEMS applications. These results are used to assess the use of thin buffers for GaN MEMS fabrication. On a 700 nm thick AlGaN/GaN epilayer, a high tensile stress is observed to increase the resonant frequency. The electromechanical coupling efficiencies of integrated transducers are assessed and compared with previously obtained results on commercially available 2 µm thick epilayers used for power transistor applications. A 28 nm V−1 actuation efficiency is measured on the 700 nm thick structure which is slightly better than the one measured on the 2 µm buffer. The electrical response of a gateless detector designed as a piezoresistance is obtained and a gauge factor of 60 is estimated. These results show that material issues can be unlocked to exploit the potentialities of III-nitrides for NEMS applications. Mode adjustment in hexagonal microresonators with an active region Ioffe Physical-Technical Institute of the RAS, St.-Petersburg, 194021, Russia Journal of Physics: Conference Series http://dx.doi.org/10.1088/1742-6596/741/1/012126

We present original types of III-nitride monocrystal microresonators with an inserted active quantum-sized region. Modelling of microresonator's modes allows us to select right parameters of a polarized quantum well (width, composition) in the way that excitation of its optical transitions would be selectively amplified by interaction with the resonator modes. Adjustment of a GaN nanocolumn resonator to an InGaN quantum well is performed.

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GANEX | Newsletter No. 45 - III-N Technology 26

GROUP 6 - Photovoltaics and Energy harvesting Group leader: Eva Monroy (INAC-CEA)

Information selected by Knowmade

Role of V-pits in the performance improvement of InGaN solar cells Georgia Tech Lorraine and CNRS, UMI2958, 57070 Metz, France Université de Lorraine and CentraleSupélec, LMOPS EA4423, 57070 Metz, France Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4963817

We study the influence of V-pits on the overall conversion efficiency of bulk In0.12In0.12 Ga0.88Ga0.88N based heterojunction solar cells grown by MOVPE. We show that V-pits significantly enhances the extraction of the photogenerated carriers in the InGaN absorber, resulting in a peak external quantum efficiency of 79% and a short circuit current density (twice the state of the art) of 2.56 mA/cm−2 under AM 1.5G conditions. Photoelectrochemical corrosion of GaN-based p-n structures University ITMO, Kronverkskiy pr. 49, St. Petersburg 197101, Russia Nitride Crystals Group Ltd., pr. Engel'sa 27, St. Petersburg 194156, Russia Herzen University, Nab. r. Moyki 48, St. Petersburg 194186, Russia Journal of Physics: Conference Series http://dx.doi.org/10.1088/1742-6596/741/1/012049

Direct water photoelectrolysis using III-N materials is a promising way for hydrogen production. GaN/AlGaN based p-n structures were used in a photoelectrochemical process to investigate the material etching (corrosion) in an electrolyte. At the beginning, the corrosion performs through the top p-type layers via channels associated with threading defects and can penetrate deep into the structure. Then, the corrosion process occurs in lateral direction in n- type layers forming voids and cavities in the structure. The lateral etching is due to net positive

charges at the AlGaN/GaN interfaces arising because of spontaneous and piezoelectric polarization in the structure and positively charged ionized donors in the space charge region of the p-n junction.

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GANEX | Newsletter No. 45 - III-N Technology 27

GROUP 7 - Materials, Technology and Fundamental Group leader: Jean-Christophe Harmand (LPN-CNRS)

NANO

Information selected by Jesús Zúñiga Pérez (CRHEA-CNRS)

Raman spectroscopy based measurements of carrier concentration in n-type GaN nanowires grown by plasma-assisted molecular beam epitaxy NIST, Applied Chemicals and Materials Division, Boulder, Colorado 80305, USA J. Appl. Phys. http://dx.doi.org/10.1063/1.4963291

The carrier concentration in as-grown ensembles of n-type GaN nanowires was determined by Raman spectroscopy of the coupled longitudinal phonon–plasmon (LPP+) mode and modeling of the carrier concentration dependence of the LPP+ frequency. The Raman measurements and analyses enabled estimation of the carrier concentration in single-nanowire devices fabricated from the as-grown ensembles. The nanowires were grown by plasma-assisted molecular beam epitaxy in either of the two growth systems. Twelve samples were examined, of which 11 samples were Si-doped and one was undoped. The Raman-measured carrier concentrations in the Si-doped samples ranged from (5.28 ± 1.19) × 1016 cm−3 to (6.16 ± 0.35) × 1017 cm−3. For a subset of samples grown with varying Si cell temperature, from 1125 °C to 1175 °C, the carrier concentration was found to be an Arrhenius function of Si cell temperature, with activation energy of 6.281±0.011 eV.6.281±0.011 eV. Co-illumination by an above band gap UV laser (325 nm, excitation intensity = 0.7 W/cm2 or 4.5 W/cm2) induced small increases in carrier concentration, relative to illumination by the Raman excitation laser alone (633 nm, excitation intensity ≈100 kW/cm2). The lowest Si-doped sample showed the largest increase in carrier concentration, (6.3 ± 4.8) × 1015 cm−3 with UV excitation intensity of 0.7 W/cm2. These results imply that, even in the absence of UV illumination,

surface depletion does not have a significant effect on the Raman carrier concentration measurements. Immersion in a high-dielectric-constant oil (ε = 2.24) caused downshifts of similar magnitude in the LPP+ frequencies of undoped and doped nanowires. This result implies that the LPP+ mode has bulk plasmon rather than surface plasmon character, because immersion in a high-dielectric-constant medium is predicted to cause a large decrease in the surface plasmon frequency, which would induce a larger LPP+ downshift in doped than undoped nanowires. A surface optical (SO) phonon peak was observed in each sample in air at ≈96.4% of the LPP+ frequency. The SO frequency decreased to ≈93.1% of the LPP+ frequency upon oil immersion, as predicted by a simple dielectric model. From single III-nitride nanowires to piezoelectric generators: New route for powering nomad electronics Laboratoire de Photonique et de Nanostructures, CNRS, Université Paris-Saclay, Route de Nozay, F-91460 Marcoussis, France Semiconductor Science and Technology http://dx.doi.org/10.1088/0268-1242/31/10/103002

Ambient energy harvesting using piezoelectric nanomaterials is today considered as a promising way to supply microelectronic devices. Since the first demonstration of electrical energy generation from piezoelectric semiconductor nanowires in 2006, the piezoelectric response of 1D-nanostructures and the development of nanowire-based piezogenerators have become a hot topic in nanoscience. After several years of intense research on ZnO nanowires, III-nitride nanomaterials have started to be explored thanks to their high piezoelectric coefficients and their strong piezogeneration response. This review describes the present status of the field of piezoelectric energy generation with nitride nanowires. After presenting the main motivation and a general overview of the domain, a short description of the main properties of III-nitride

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nanomaterials is given. Then we review the piezoelectric responses of III-N nanowires and the specificities of the piezogeneration mechanism in these nanostructures. Finally, the design and performance of the macroscopic piezogenerators based on nitride nanowire arrays are described, showing the promise of III-nitride nanowires for ultra-compact and efficient piezoelectric generators. Self-induced GaN nanowire growth: surface density determination St. Petersburg Academic University, 8/3 Khlopina, St.Petersburg' 194021, Russia ITMO University, 49 Kronverkskiy pr., 197101, St. Petersburg, Russia Journal of Physics: Conference Series http://dx.doi.org/10.1088/1742-6596/741/1/012032

A new numerical approach for the determination of the GaN nanowire surface density on an AlN/Si substrate as a function of the growth time and gallium flux is presented. Within this approach, the GaN island solid-like coalescence and island-nanowire transition are modeled by the Monte-Carlo method. We show the importance of taking into consideration the island coalescence for explaining that the maximum of GaN island surface density is several times larger than the maximum of GaN nanowire surface density. Also, we find that the nanowire surface density decreases with an increase of the gallium flux. Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy Institute of Materials Science (ICMUV), Universidad de Valencia, PO Box 22085, E-46071, Valencia, Spain CIMAP, UMR 6252, ENSICAEN, 6 Bd Maréchal Juin, F-14050 Caen Cedex 4, France Nanotechnology http://dx.doi.org/10.1088/0957-4484/27/38/385202

Making use of Kelvin probe force microscopy, in dark and under ultraviolet illumination, we study the characteristics of p–n junctions formed along the axis of self-organized GaN nanowires (NWs). We map the contact potential difference of the single NW p–n junctions to locate the space charge region and directly measure the depletion

width and the junction voltage. Simulations indicate a shrinkage of the built-in potential for NWs with small diameter due to surface band bending, in qualitative agreement with the measurements. The photovoltage of the NW/substrate contact is studied by analyzing the response of NW segments with p- and n-type doping under illumination. Our results show that the shifts of the Fermi levels, and not the changes in surface band bending, are the most important effects under above band-gap illumination. The quantitative electrical information obtained here is important for the use of NW p–n junctions as photovoltaic or rectifying devices at the nanoscale, and is especially relevant since the technique does not require the formation of ohmic contacts to the NW junction. A review of the electrical properties of semiconductor nanowires: insights gained from terahertz conductivity spectroscopy Department of Engineering, University of Cambridge, Electrical Engineering Building, 9 JJ Thomson Avenue, Cambridge, CB3 0FA, UK Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK Semiconductor Science and Technology http://dx.doi.org/10.1088/0268-1242/31/10/103003

Accurately measuring and controlling the electrical properties of semiconductor nanowires is of paramount importance in the development of novel nanowire-based devices. In light of this, terahertz (THz) conductivity spectroscopy has emerged as an ideal non-contact technique for probing nanowire electrical conductivity and is showing tremendous value in the targeted development of nanowire devices. THz spectroscopic measurements of nanowires enable charge carrier lifetimes, mobilities, dopant concentrations and surface recombination velocities to be measured with high accuracy and high throughput in a contact-free fashion. This review spans seminal and recent studies of the electronic properties of nanowires using THz spectroscopy. A didactic description of THz time-domain spectroscopy, optical pump–THz probe spectroscopy, and their application to nanowires is included. We review a variety of technologically important nanowire materials, including GaAs,

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InAs, InP, GaN and InN nanowires, Si and Ge nanowires, ZnO nanowires, nanowire heterostructures, doped nanowires and modulation-doped nanowires. Finally, we discuss how THz measurements are guiding the development of nanowire-based devices, with the example of single-nanowire photoconductive THz receivers.

NON/SEMI POLAR Information selected by

Philippe De Mierry (CRHEA-CNRS) Dynamic characteristics of 410 nm semipolar (202¯1¯) III-nitride laser diodes with a modulation bandwidth of over 5 GHz Materials Department, University of California, Santa Barbara, California 93106, USA Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4962430

The dynamic characteristics of III-nitride multi-quantum well laser diodes (LDs) emitting at 410 nm were investigated. LDs were grown on semipolar (202¯1¯)(202¯1¯) bulk GaN substrates and fabricated into devices with cavity lengths ranging from 900 nm to 1800 nm. A 3-dB bandwidth of 5 GHz and 5 Gbit/s direct modulation with on-off keying were demonstrated, which were limited by the bandwidth of the photodetector used for the measurements. The differential gain of the LDs was determined to be 2.5 ± 0.5 × 10−16 cm2 by comparing the slope efficiency for different cavity lengths. Analysis of the frequency response showed that the K-factor, the gain compression factor, and the intrinsic maximum bandwidth were 0.33 ns, 7.4 × 10−17 cm3, and 27 GHz, respectively. Facet analysis of truncated pyramid semi-polar GaN grown on Si(100) with rare-earth oxide interlayer Institute of Applied Research, Vilnius University, Saulėtekio 10, 10223 Vilnius, Lithuania Translucent Inc., 952 Commercial St., Palo Alto, California 94303, USA

The Cambridge Centre for Gallium Nitride, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom J. Appl. Phys. http://dx.doi.org/10.1063/1.4962312

After epitaxial growth of GaN on Si(100) substrates using an Er2O3Er2O3 interlayer, two dominant growth orientations can be observed: semi-polar (101¯3)(101¯3) as well as non-polar (112¯0)(112¯0). Epilayers with the (101¯3)(101¯3) orientation lead to the formation of truncated pyramids, which were studied in detail by high-resolution X-ray diffraction, photoluminescence, and scanning electron microscopy (SEM). Depending on the GaN growth orientation and in-plane relation to the Er2O3Er2O3 interlayer, lattice mismatches in the growth plane were calculated. In order to understand the formation of truncated pyramids, a method for facet identification from SEM images under different tilt angles was developed. This method was used to reconstruct truncated pyramids from our experiments. These were then compared with calculations of the corresponding kinetic Wulff construction, to explain the preferential growth of (101¯3)(101¯3) GaN. High Bandwidth Freestanding Semipolar (11–22) InGaN/GaN Light-Emitting Diodes Tyndall National Institute, University College Cork, Cork, Ireland IEEE Photonics Journal http://dx.doi.org/10.1109/JPHOT.2016.2596245

Freestanding semipolar (11–22) indium gallium nitride (InGaN) multiple-quantum-well light-emitting diodes (LEDs) emitting at 445 nm have been realized by the use of laser lift-off (LLO) of the LEDs from a 50- μm- thick GaN layer grown on a patterned (10–12) r- plane sapphire substrate (PSS). The GaN grooves originating from the growth on PSS were removed by chemical mechanical polishing. The 300 μm × 300 μm LEDs showed a turn-on voltage of 3.6 V and an output power through the smooth substrate of 0.87 mW at 20 mA. The electroluminescence spectrum of LEDs before and after LLO showed a stronger emission intensity along the [11–23] InGaN/GaN

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direction. The polarization anisotropy is independent of the GaN grooves, with a measured value of 0.14. The bandwidth of the LEDs is in excess of 150 MHz at 20 mA, and back-to-back transmission of 300 Mbps is demonstrated, making these devices suitable for visible light communication (VLC) applications. Semipolar III–nitride light-emitting diodes with negligible efficiency droop up to ~1 W Department of Electrical and Computer Engineering, University of California, Santa Barbara, CA 93106, U.S.A. Materials Department, University of California, Santa Barbara, CA 93106, U.S.A. Applied Physics Express http://dx.doi.org/10.7567/APEX.9.102102

We demonstrate 1 mm2 blue light-emitting diodes with a negligible efficiency droop up to ~1 W. LEDs with 12- to 14-nm-thick single quantum wells were grown by metalorganic chemical vapor deposition on a free-standing semipolar $(20\bar{2}\bar{1})$ GaN substrate. Packaged devices showed an external quantum efficiency of 42.3% at 20 A/cm2 with a negligible efficiency droop up to 991 mW at 900 mA. At 900 mA, the thermal droop and hot/cold factor were 8.2% and 0.92, respectively. The adoption of a thick active region resulted in excellent optical and thermal performance characteristics that are suitable for high-power lighting applications.

OTHER (fundamental, material, characterization, equipment)

Information selected by Agnès Trassoudaine (Université d'Auvergne)

and Yvon Cordier (CRHEA-CNRS)

Growth of hexagonal boron nitride on (111) Si for deep UV photonics and thermal neutron detection Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4962831

Hexagonal boron nitride (hBN) growth was carried out on (111) Si substrates at a temperature of

1350 °C using a cold wall chemical vapor deposition system. The hBN phase of the deposited films was identified by the characteristic Raman peak at 1370 cm−1 with a full width at half maximum of 25 cm−1, corresponding to the in-plane stretch of B and N atoms. Chemical bonding states and composition of the hBN films were analyzed by X-ray photoelectron spectroscopy; the extracted B/N ratio was 1.03:1, which is 1:1 within the experimental error. The fabricated metal-hBN-metal devices demonstrate a strong deep UV (DUV) response. Further, the hBN growth on the vertical (111) surfaces of parallel trenches fabricated in (110) Si was explored to achieve a thermal neutron detector. These results demonstrate that hBN-based detectors represent a promising approach towards the development of DUV photodetectors and efficient solid-state thermal neutron detectors. Resonant and nonresonant vibrational excitation of ammonia molecules in the growth of gallium nitride using laser-assisted metal organic chemical vapour deposition Department of Electrical and Computer Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0511, USA J. Appl. Phys. http://dx.doi.org/10.1063/1.4962426

The influence of exciting ammonia (NH3) molecular vibration in the growth of gallium nitride (GaN) was investigated by using an infrared laser-assisted metal organic chemical vapor deposition method. A wavelength tunable CO2 laser was used to selectively excite the individual vibrational modes. Resonantly exciting the NH-wagging mode (v 2) of NH3 molecules at 9.219 μm led to a GaN growth rate of 84 μm/h, which is much higher than the reported results. The difference between the resonantly excited and conventional thermally populated vibrational states was studied via resonant and nonresonant vibrational excitations of NH3 molecules. Resonant excitation of various vibrational modes was achieved at 9.219, 10.35, and 10.719 μm, respectively. Nonresonant excitation was conducted at 9.201 and 10.591 μm, similar to

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GANEX | Newsletter No. 45 - III-N Technology 31

conventional thermal heating. Compared to nonresonant excitation, resonant excitation noticeably promotes the GaN growth rate and crystalline quality. The full width at half maximum value of the XRD rocking curves of the GaN (0002) and GaN (10–12) diffraction peaks decreased at resonant depositions and reached its minimum value of 45 and 53 arcmin, respectively, at the laser wavelength of 9.219 μm. According to the optical emission spectroscopic studies, resonantly exciting the NH3 v 2 mode leads to NH3 decomposition at room temperature, reduces the formation of the TMGa:NH3 adduct, promotes the supply of active species in GaN formation, and, therefore, results in the increased GaN growth rate. Temperature and doping dependent changes in surface recombination during UV illumination of (Al)GaN bulk layers Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin, Germany J. Appl. Phys. http://dx.doi.org/10.1063/1.4962319

We have studied the effect of continuous illumination with above band gap energy on the emission intensity of polar (Al)GaN bulk layers during the photoluminescence experiments. A temporal change in emission intensity on time scales from seconds to hours is based on the modification of the semiconductor surface states and the surface recombination by the incident light. The temporal behavior of the photoluminescence intensity varies with the parameters such as ambient atmosphere, pretreatment of the surface, doping density, threading dislocation density, excitation power density, and sample temperature. By means of temperature-dependent photoluminescence measurements, we observed that at least two different processes at the semiconductor surface affect the non-radiative surface recombination during illumination. The first process leads to an irreversible decrease in photoluminescence intensity and is dominant around room temperature, and the second process leads to a delayed increase in intensity and becomes

dominant around T = 150–200 K. Both processes become slower when the sample temperature decreases from room temperature. They cease for T < 150 K. Stable photoluminescence intensity at arbitrary sample temperature was obtained by passivating the analyzed layer with an epitaxially grown AlN cap layer. Magneto transport in crossed electric and magnetic fields in compensated bulk GaN Institute of Semiconductor Physics, NAS of Ukraine, 41, Prospect Nauky, 03028 Kyiv, Ukraine J. Appl. Phys. http://dx.doi.org/10.1063/1.4962215

Low-temperature high-field electron transport is studied for compensated bulk GaN subjected to crossed electric and magnetic fields. The electron kinetics, distribution function, and field dependencies of the magneto transport characteristics are analyzed by using the Monte-Carlo method. At zero magnetic field, for an ionized impurity concentration of 1016 cm−3 and an electron concentration of 1015 cm−3, it is shown that dissipative streaming transport with a strong anisotropic electron distribution in the momentum space is realized at electric fields in the range 3−103−10 kV/cm and for a lattice temperature of 30 K. The magnetic field destroys the dissipative streaming transport. Indeed, for a magnetic field greater than 4 T, the electrons are predominantly confined in a region of the momentum space where their energy is smaller than the optical phonon energy and the strong inelastic scattering by optical phonons is practically eliminated. A quasi-ballistic electron transport occurs in the form of a vortex-like motion in the momentum space. The axis of rotation of this vortex coincides with the average electron momentum. A general analysis of the distribution function suitable for any configuration of the Hall circuit is presented. The main magneto transport characteristics (dissipative current, Hall current, and Hall electric field) are studied for the short and open Hall circuits. We show that the magneto transport measurements can provide valuable information on the main features of the electron distribution function and electron dynamics in GaN. Finally, we suggest that the

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strong dependency of the dissipative current on the parameters of the Hall circuit can be used for current modulation and current switching. High pressure and time resolved studies of optical properties of n-type doped GaN/AlN multi-quantum wells: Experimental and theoretical analysis Institute of Physics Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02-668 Warsaw, Poland Cardinal Stefan Wyszynski University, College of Science, Department of Mathematics and Natural Sciences, Dewajtis 5, 01-815 Warsaw, Poland Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland University of Warsaw, Faculty of Physics, Pasteura 5, 02-093 Warsaw, Poland Université Grenoble-Alpes, 38000 Grenoble, France CEA Grenoble, INAC-PHELIQS, 17 av. des Martyrs, 38000 Grenoble, France J. Appl. Phys. http://dx.doi.org/10.1063/1.4962282

High-pressure and time-resolved studies of the optical emission from n-type doped GaN/AlN multi-quantum-wells (MQWs) with various well thicknesses are analysed in comparison with ab initio calculations of the electronic (band structure, density of states) and optical (emission energies and their pressure derivatives, oscillator strength) properties. The optical properties of GaN/AlN MQWs are strongly affected by quantum confinement and polarization-induced electric fields. Thus, the photoluminescence (PL) peak energy decreases by over 1 eV with quantum well (QW) thicknesses increasing from 1 to 6 nm. Furthermore, the respective PL decay times increased from about 1 ns up to 10 μs, due to the strong built-in electric field. It was also shown that the band gap pressure coefficients are significantly reduced in MQWs as compared to bulk AlN and GaN crystals. Such coefficients are strongly dependent on the geometric factors such as the thickness of the wells and barriers. The transition energies, their oscillator strength, and pressure dependence are modeled for tetragonally strained structures of the same geometry using a full tensorial representation of the strain in the MQWs under external pressure. These MQWs were simulated directly using

density functional theory calculations, taking into account two different systems: the semi-insulating QWs and the n-doped QWs with the same charge density as in the experimental samples. Such an approach allowed an assessment of the impact of n-type doping on optical properties of GaN/AlN MQWs. We find a good agreement between these two approaches and between theory and experimental results. We can therefore confirm that the nonlinear effects induced by the tetragonal strain related to the lattice mismatch between the substrates and the polar MQWs are responsible for the drastic decrease of the pressure coefficients observed experimentally. I2 basal stacking fault as a degradation mechanism in reverse gate-biased AlGaN/GaN HEMTs Department of Materials Science and Engineering, Drexel University, 3141 Chestnut Street, Philadelphia, Pennsylvania 19104, USA Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4963156

Here, we present the observation of a bias-induced, degradation-enhancing defect process in plasma-assisted molecular beam epitaxy grown reverse gate-biased AlGaN/GaN high electron mobility transistors (HEMTs), which is compatible with the current theoretical framework of HEMT degradation. Specifically, we utilize both conventional transmission electron microscopy and aberration-corrected transmission electron microscopy to analyze microstructural changes in not only high strained regions in degraded AlGaN/GaN HEMTs but also the extended gate-drain access region. We find a complex defect structure containing an I2 basal stacking fault and offer a potential mechanism for device degradation based on this defect structure. This work supports the reality of multiple failure mechanisms during device operation and identifies a defect potentially involved with device degradation.

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Investigation of interface abruptness and In content in (In,Ga)N/GaN superlattices Paul-Drude-Institut für Festkörperelektronik, Leibniz-Institut im Forschungsverbund Berlin e.V, Hausvogteiplatz 5–7, 10117 Berlin, Germany TopGaN sp. z o. o., Sokolowska 29/37, 01-142 Warsaw, Poland Laboratory for Solid State Physics, ETH Zürich, Otto-Stern-Weg 1, CH-8093 Zurich, Switzerland J. Appl. Phys. http://dx.doi.org/10.1063/1.4963273

We investigate designed InN/GaN superlattices (SLs) grown by plasma-assisted molecular beam epitaxy on c-plane GaN templates in situ by line-of-sight quadrupole mass spectroscopy and laser reflectivity, and ex situ by scanning transmission electron microscopy, X-ray diffraction, and photoluminescence (PL). The structural methods reveal concordantly the different interface abruptness of SLs resulting from growth processes with different parameters. Particularly crucial for the formation of abrupt interfaces is the Ga to N ratio that has to be bigger than 1 during the growth of the GaN barriers, as Ga-excess GaN growth aims at preventing the unintentional incorporation of In accumulated on the growth surface after the supply of InN, that extends the (In,Ga)N quantum well (QW) thickness. Essentially, even with GaN barriers grown under Ga-excess yielding to 1 monolayer (ML) thick QWs, there is a real discrepancy between the designed binary InN and the actual ternary (In,Ga)N ML thick QWs revealed by the above methods. The PL emission line of the sample with atomically abrupt interfaces peaks at 366 nm, which is consistent with the In content measured to be less than 10%. Strain and compositional fluctuations in Al0.81In0.19NAl0.81In0.19N/GaN heterostructures Peter Grünberg Institut, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany Appl. Phys. Lett. http://dx.doi.org/10.1063/1.4963184

The strain and compositional fluctuations of nearly lattice-matched

Al0.81In0.19NAl0.81In0.19N/GaN heterostructures are investigated by cross-sectional scanning tunneling microscopy and selected area electron diffraction measurements in scanning electron transmission microscopy. The presence of strain induces height modulations governed by different roughness components at the cleavage surfaces. The surface height modulations are compatible with a relaxation of alternatingly compressive and tensile strained domains, indicating compositional fluctuations. Changes of the a lattice constant are traced to interface misfit edge dislocations. The dislocations induce steps increasing the roughness within the Al0.81In0.19NAl0.81In0.19N layers. Modeling of the wafer bow in GaN-on-Si epiwafers employing GaN/AlN multilayer buffer structures Innovation Center for Multi-Business of Nitride Semiconductors, Nagoya Institute of Technology, Nagoya 466-8555, Japan Research Center for Nano Devices and Advanced Materials, Nagoya Institute of Technology, Nagoya 466-8555, Japan Semiconductor Science and Technolog http://dx.doi.org/10.1088/0268-1242/31/10/105016

We built a calculation model for the wafer bow in GaN-on-Si epiwafers employing GaN/AlN multilayer (ML) buffer structures by extending Stoney's equation. The calculated bow and the derived strain in the epilayers were almost consistent with experimental results. The calculation quantitatively revealed that the ML buffers introduced an in-plane compressive stress in the epitaxial structures. Also, relationships between the epiwafer bow and the stress in the respective layers became clear to a certain extent. For instance, when considering the case where periodic structures with 20 nm thick GaN/5 nm thick AlN pairs were grown as ML buffers on 4-in.-diameter and 525 μm thick Si (111) substrates at a growth temperature (T g) of 1125 °C, the stress in the MLs was derived to be 2.18 GPa in the in-plane compressive direction in the GaN layers and 5.89 GPa in the in-plane tensile direction in the AlN layers at T g. Although magnitude of the in-plane stress in the GaN layers is obviously smaller than that in the AlN layers, the restoring force

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generated in the GaN layers becomes larger than that in the AlN layers, because the force is in proportion to the layer thickness rather than to just the stress. As a consequence, the generated stress in the MLs was considered to produce enough force to suppress the epiwafer bow. The calculation also demonstrated that GaN epilayers on GaN/AlN MLs were strained in the in-plane compressive direction at T g and almost strain-free at room temperature. Influence of AlN/GaN superlattice period on frequency of polar optical modes Physical faculty, St.Petersburg State University, 199034 St. Petersburg, Russia Resource Center for Optical and Laser Materials Research, St. Petersburg State University, St. Petersburg, 199034 St. Petersburg, Russia Journal of Physics: Conference Series http://dx.doi.org/10.1088/1742-6596/741/1/012123

Polar optical phonons in the binary AlN/GaN superlattices (SL) were studied in the framework of dielectric continuum model (DCM). It is shown that the modes propagating in the interface plane are delocalized over all layers and the modes propagating along the SL axis are delocalized in certain layers. Frequencies of former strongly depend on the layer thickness ratio and frequencies of the latter do not depend on the SL structure. Such behavior is typical for the short-period SL. We show that a strong coupling between two types of the modes takes place at increasing SL period. The phenomenon is described mathematically by the frequency- structure relations and its physical meaning is discussed. Separation of stress-free AlN/SiC thin films from Si substrate St. Petersburg Academic University, St. Petersburg 194021, Russia Institute of Problems of Mechanical Engineering RAS, St. Petersburg 199178, Russia ITMO University, St. Petersburg 197101, Russia Peter the Great St. Petersburg Polytechnic University, St. Petersburg 195251, Russia Journal of Physics: Conference Series http://dx.doi.org/10.1088/1742-6596/741/1/012034

We separated AlN/SiC film from Si substrate by chemical etching of the AlN/SiC/Si heterostructure. The film fully repeats the size and geometry of the original sample and separated without destroying. It is demonstrated that a buffer layer of silicon carbide grown by a method of substitution of atoms may have an extensive hollow subsurface structure, which makes it easier to overcome the differences in the coefficients of thermal expansion during the growth of thin films. It is shown that after the separation of the film from the silicon substrate, mechanical stresses therein are almost absent. Control of stress and threading dislocation density in the thick GaN/AlN buffer layers grown on Si (111) substrates by low- temperature MBE Ioffe Institute, Polytekhnicheskaya 26, St. Petersburg 194021, Russia Journal of Physics: Conference Series http://dx.doi.org/10.1088/1742-6596/741/1/012025

We report on successful growth by plasma-assisted molecular beam epitaxy on a Si(111) substrate crack-free GaN/AlN buffer layers with a thickness more than 1 μm. The layers fabricated at relatively low growth temperature of 780°C have at room temperature the residual compressive stress of -97 MPa. Intrinsic stress evolution during the GaN growth was monitored in situ with a multi-beam optical system. Strong dependence of a stress relaxation ratio in the growing layer vs growth temperature was observed. The best-quality crack-free layers with TDs density of ~⃒109 cm-2 and roughly zero bowing were obtained in the sample with sharp 2D-GaN/2D-AlN interface. Synchrotron radiation X-ray photoelectron spectroscopy of Ti/Al ohmic contacts to n-type GaN: Key role of Al capping layers in interface scavenging reactions Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan Panasonic Corporation, Nagaokakyo, Kyoto 617-8520, Japan Japan Atomic Energy Agency, Sayo, Hyogo 679-5148, Japan

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Applied Physics Express http://dx.doi.org/10.7567/APEX.9.105801

Interface reactions between Ti-based electrodes and n-type GaN epilayers were investigated by synchrotron radiation X-ray photoelectron spectroscopy. Metallic Ga and thin TiN alloys were formed at the interface by subsequently depositing Al capping layers on ultrathin Ti layers even at room temperature. By comparing results from stacked Ti/Al and single Ti electrodes, the essential role of Al capping layers serving as an oxygen-scavenging element to produce reactive Ti underlayers was demonstrated. Further growth of the metallic interlayer during annealing was observed. A strategy for achieving low-resistance ohmic contacts to n-GaN with low-thermal-budget processing is discussed. Tri-halide vapor-phase epitaxy of GaN using GaCl3 on polar, semipolar, and nonpolar substrates Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan Applied Physics Express http://dx.doi.org/10.7567/APEX.9.105501

Homoepitaxial tri-halide vapor-phase epitaxy (THVPE) growth on polar, semipolar, and nonpolar bulk GaN substrates was demonstrated using GaCl3 as the precursor. The influence of the surface orientation of the substrate on GaN growth by THVPE was compared with that observed for GaN grown by hydride vapor-phase epitaxy. The dependence of the GaN growth on the surface orientation of the substrate was confirmed; GaN could be grown on $(10\bar{1}0)$, $(30\bar{3}\bar{1})$, $(20\bar{2}\bar{1})$, $(10\bar{1}\bar{1})$, and $(000\bar{1})$ but not on $(0001)$, $(10\bar{1}1)$, $(20\bar{2}1)$, or $(30\bar{3}1)$. This behavior was explained to be due to the changes in adsorption energy, the magnitudes of which were estimated by theoretical calculations.

Mechanism of hot electron electroluminescence in GaN-based transistors Center for Device Thermography and Reliability, H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK Journal of Physics D: Applied Physics http://dx.doi.org/10.1088/0022-3727/49/43/435101

The nature of hot electron electroluminescence (EL) in AlGaN/GaN high electron mobility transistors is studied and attributed to Bremsstrahlung. The spectral distribution has been corrected, for the first time, for interference effects due to the multilayered device structure, and this was shown to be crucial for the correct interpretation of the data, avoiding artefacts in the spectrum and misinterpretation of the results. An analytical expression for the spectral distribution of emitted light is derived assuming Bremsstrahlung as the only origin and compared to the simplified exponential model for the high energy tail commonly used for electron temperature extraction: the electron temperature obtained results about 20% lower compared to the approximated exponential model. Comparison of EL intensity for devices from different wafers illustrated the dependence of EL intensity on the material quality. The polarization of electroluminescence also confirms Bremsstrahlung as the dominant origin of the light emitted, ruling out other possible main mechanisms. Density functional theory study : Electronic structures of RE:GaN in wurtzite Gα15RE1N16 Computational Sciences, Institut Teknologi Bandung, Indonesia Center for Nuclear Reactor Technology and Safety, PTKRN-BATAN, Indonesia Division of Mathematical and Physical Science, Graduate School of Natural Science and Technology, Kanazawa University, Japan Physics of Earth and Complex Systems, Institut Teknologi Bandung, Indonesia Journal of Physics: Conference Series http://dx.doi.org/10.1088/1742-6596/739/1/012027

Gallium nitride (GaN) is a wide-band gap (Eg=3.4eV) semiconductor. Rare-earth (RE) in GaN have attracted interest due to their potential

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applications. Electronic structure calculations were performed for substitutional rare-earth (Pr, Er, Eu, Nd, and Dy) in wurtzite supercell GaN using density functional theory calculations within the GGA approach. Our calculations show that RE doped in GaN exhibit an indirect band gap and introduces an impurity level. We found the equilibrium bond lengths of RE-N are vary between 2.13 to 2.253Å in good agreement with structural data available for Eu and Er. We confirm that the present supercell model well describes the state of RE in GaN. Its predicts the band gap narrowing that expected to improve the optical performance of GaN.

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PRESS RELEASE Technical and economic information selected by Knowmade

OPTOELECTRONICS

Seoul Semiconductor Sues Kmart over Patent Infringement LEDinside

Korean LED manufacturer Seoul Semiconductor has filed a lawsuit against Kmart, claiming the American retail franchise was selling LED products that violated its patents, reported The Korea Herald. Seoul Semiconductor accused Kmart for infringing eight patents that cover high Color Rendering Index (CRI), phosphor related combinations, LED epitaxal growth, LED chip production, and multi-chip mounting technology, omni-directional LED lamp and Acrich multi-junction technology. The LED company said the products being sold in Kmart infringed eight of its patents including high CRI, or color rendering index, enhancement with phosphor combinations, LED epitaxial growth, LED chip fabrication, multi-chip mounting technology, omni-directional LED lamp technology and Acrich multi junction technology. “We have invested tremendous resources for environment-friendly technology innovation for 25 years,” said Nam Ki-bum, vice president of Seoul Semiconductor’s lighting business department. The allegedly patent infringed products include those that feature LED patents filed by Nobel laureate Nakamura Shuji and fellow UC Santa Barbara colleague Steven DenBaars. LED filament bulbs were also included in the patent lawsuit, a product that has attracted widespread consumer attention in the U.S. as more consumers replace traditional incandescent bulbs with LEDs.

According to the report, Seoul Semiconductor has won 50 suits against competitors, including Taiwanese tech company AOT in 2003. The company has also clinched a patent lawsuit victory against the U.S. based LED TV manufacturer Craig Electronics last year, and a jury verdict against Japanese lens maker Enplas in 2016, which demanded Enplas to pay a compensation of US $4 million over LED patent infringement. The LED manufacturer said it is working with U.S.-based law firm Latham & Watkins to work with Larry Gotts, who lead the counsel of Seoul Semiconductor’s lawsuit against Enplas. Read more Soraa launches Vivid GU24 base PAR20, PAR30 and PAR38 directional LED lamps Semiconductor Today

Soraa Inc of Fremont, CA, USA, which develops solid-state lighting technology fabricated on 'GaN on GaN' (gallium nitride on gallium nitride) substrates, has added GU24 base PAR20, PAR30 (short and long neck) and PAR38 LED lamps to its LED product portfolio. Suitable for both commercial and residential California applications, Soraa's lamps provide a replacement for halogen lamps. “California lighting designers and customers have been asking for high-quality large GU24 lamps,” according to George Stringer, senior VP of global sales & marketing. “With low power consumption, unique narrow spot beams enabled by our Point Source Optics and our Violet-Emission 3-Phosphor technology; these lamps completely outshine the competition,” he claims. Soraa's Point Source Optics technology is said to produce high-intensity and uniform beams, enabling the firm to offer 8, 9 and 10° narrow-spot PAR versions with double the peak intensity of other LED makers, it is claimed.

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Soraa's Violet-Emission 3-Phosphor (VP3) LED technology allows the rendering of colors and whiteness. Utilizing every color in the rainbow, especially deep red emission, VP3 Vivid Color renders warm tones accurately, and achieves a color-rendering index (CRI) of 95 and deep red (R9) rendering of 95. Also, unlike blue-based white LEDs without any violet emission, the VP3 Natural White is achieved by engineering the violet emission to properly excite fluorescing brightening agents including natural objects like human eyes and teeth; as well as manufactured white materials such as clothing, paper and cosmetics. Designed for seamless fixture integration, Soraa's GU24 PAR lamps are compatible with a wide variety of dimmers and are suitable for use in enclosed, non-ventilated indoor and outdoor fixtures. They are available in 8, 9, 10, 25, 36, 50 and 60° beam angles as well as 2700K, 3000K, 4000K and 5000K color temperatures. Additionally, the 8, 9, and 10° lamps work the firm's its magnetic accessory SNAP System. With a simple magnetic accessory attachment, beam shapes can be altered and color temperature can be modified, increasing design and display possibilities. Read more Chinese LED maker HC SemiTek orders Veeco MOCVD systems for high-volume production Semiconductor Today

Epitaxial deposition and process equipment maker Veeco Instruments Inc of Plainview, NY, USA says that solid-state lighting manufacturer HC SemiTek Corp of Wuhan, China (which supplies full-spectrum visible light LED chips) has ordered multiple TurboDisc EPIK 700 GaN (gallium nitride) metal-organic chemical vapor deposition (MOCVD) systems and the TurboDisc K475i As/P (arsenic phosphide) MOCVD system for high-volume LED production. HC SemiTek says that it ordered the systems on the basis of the award-winning EPIK platform and its own experience with other Veeco MOCVD reactors, including the TurboDisc MaxBright, K465i and K475 MOCVD systems. The EPIK and K475i systems will be installed to meet market demand

driven by the need for high performance LEDs in lighting and fine-pitch displays. “The seamless process transfer between legacy and new Veeco platforms made this an easy decision,” comments HC SemiTek's president Dr Rong Liu. “Adding the EPIK and K475i systems to our production fleet ensures we can achieve the most optimal device performance while lowering our cost of ownership to accelerate our company's growth objectives.” “HC SemiTek, a leader in the Chinese LED market, has long been a valuable and important customer to Veeco,” comments Veeco's president William J. Miller Ph.D. Introduced in 2014, the EPIK 700 MOCVD system is reckoned to be the LED industry's highest-productivity system for blue/green LEDs. Introduced earlier this year, the K475i system can be used to make red, orange and yellow LEDs, as well as multi-junction III-V solar cells, laser diodes and transistors. Based on Veeco's proven TurboDisc technology and the proprietary Uniform FlowFlange, Veeco says that its MOCVD systems enable users to achieve cost per wafer savings of up to 20% compared with previous MOCVD systems through improved wafer uniformity, reduced operating expenses and increased productivity. Read more

ELECTRONICS

Advantech Wireless releases second-generation GaN-based 125-200W Ka-band SSPA/BUC Semiconductor Today

Advantech Wireless Inc of Montreal, Canada (which manufactures satellite, RF equipment and microwave systems) has launched its second-generation gallium nitride (GaN)-based 125-200W Ka-band UltraLinear solid-state power amplifier/block up-converter (SSPA/BUC) products. They follow the firm's 100W Ka-band

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GaN-based units (which have been adopted by several military organizations). The new UltraLinear GaN-based SSPAs are designed to operate in harsh outdoor environments and have been designed for Ka-band low Earth orbit (LEO) and geostationary orbit (GEO) satellite up-link applications. The GaN-based SSPB-4010Ka series comprise integrated units, complete with detachable power supply, phase-locked oscillator, mixer, filter and proprietary cooling mechanism. Intended for outdoor operation, the second-generation GaN-based systems are claimed to be the most advanced GaN-based Ka-band units on the market, providing higher power and higher reliability. “Ka-band solid-state technology has been part of Advantech Wireless' product development roadmap since 2000, when we developed the first worldwide Ka-band terminal to be Mil certified by the precursor of what we now know as WGS,” says Cristi Damian, VP business development. “GaN technology allows us to reach power levels that were not possible before, and to serve customers that are looking for solutions in this fast-growing market segment.” Advantech Wireless is exhibiting in booth 1.F40 at IBC 2016 in Amsterdam, The Netherlands (9-13 September). Read more GaN device market to grow at 17% CAGR to $3438.4m in 2024 Semiconductor Today

The global gallium nitride (GaN) device market is largely consolidated, with the top four companies collectively commanding more than 65% market share in 2015, states Transparency Market Research (TMR) in the report 'GaN Semiconductor Devices Market - Global Industry Analysis, Size, Share, Growth, Trends and Forecast, 2016-2024'. The dominant firm Efficient Power Conversion Corp (EPC) accounted for 19.2% of the market, followed by NXP Semiconductors N.V., GaN Systems Inc, and Cree Inc.

Regarding on-going R&D activities, efforts to eliminate issues related to the reliability of GaN semiconductors are expected to be an important focus of key vendors in the near future. Transparency Market Research forecasts that the GaN device market will rise at a compound annual growth rate (CAGR) of 17% over 2016-2024, increasing from $870.9m in 2015 to $3438.4m in 2024. Of the key end-use industries utilizing GaN, the aerospace & defense sector dominates, accounting for over 42% of the market in 2015. Broadening applications and focus on R&D to boost demand in North America and Europe North America and Europe are expected to remain the dominant regional markets for GaN devices over the next few years. The rising focus of the Europe Space Agency (ESA) on the increased usage of GaN across space projects and the use of GaN-based transistors in the military and defense sectors in North America will help the GaN device market to gain traction, reckons the report. In the past few years, GaN technology has seen rapid advances and vast improvement in its ability to work under operating environments featuring high frequency, power density and temperature with improved linearity and efficiency. These advances have boosted the usage of GaN devices across an increased set of applications and have played an important role in the market's overall growth, notes the report. In addition, the increased usage of GaN devices in the defense sector has emerged as a key market driver. The continuous rise in defense budgets of developing and developed countries as well as the demand for inclusion of the most advanced products in the arsenal of national and international military will propel the market in the near future. High cost to hinder growth Compared with silicon-based devices, GaN-based devices are relatively expensive due to the high production costs, including the high cost of fabrication, packaging and support electronics. Silicon-based semiconductors have seen a

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significant decline in their costs over the past few years, making the high cost of GaN a challenge that could hinder its large-scale adoption. The issue can be tackled by producing GaN in bulk. However, there is currently no widespread method that can be used for this purpose due to the necessity for high operating pressure and temperature as well as the limited scalability of the material, concludes the report. Read more Wolfspeed completes C-band radar range with 70W GaN HEMT pre-driver operating at 4.5–5.9GHz Semiconductor Today

Wolfspeed of Research Triangle Park, NC, USA — a Cree Company that makes gallium nitride on silicon carbide (GaN-on-SiC) high-electron-mobility transistors (HEMTs) and monolithic microwave integrated circuits (MMICs) — has announced its complete lineup of high-efficiency, high-gain and wide-bandwidth devices for C-band radar systems with the introduction of its CGHV59070 GaN HEMT, which will be on display in booth #156 at European Microwave Week (EuMW 2016) at ExCel London, UK (3–7 October). Designed to operate at 4.5–5.9GHz from a 50V rail, the new 70W GaN HEMT is suitable as a driver for the 350W CGHV59350 GaN HEMT for 5.2–5.9GHz operation (launched in May 2015), which is claimed to be the highest-power C-band radar device on the market. Delivering 90W typical POUT at 50V, in addition to 55% drain efficiency at high 14dB power gain, the internally matched CGHV59070 offers a general-purpose broadband solution for RF and microwave applications, and is especially suitable for use in linear and compressed amplifier circuits in marine radar, weather monitoring, air & maritime vessel traffic control, and port security applications. “First demonstrated at this year's International Microwave Symposium [IMS 2016 in late May], the market release of the new 70W CGHV59070 pre-driver completes Wolfspeed's C-band radar lineup of pre-drivers, drivers and output stages, enabling 1kW, all-GaN SSPAs [solid-state power

amplifiers] for C-band radar applications,” says RF & microwave director Jim Milligan. “This latest introduction also further extends our comprehensive radar product portfolio, which helps designers achieve smaller, lighter and higher-power RF amplifiers that are critical for the development of the next-gen military, aerospace and commercial radar applications.” The CGHV59070 can be supplied in a ceramic/metal flange or pill package, and can be shipped either individually or alongside or installed on a test board. Wolfspeed says that, compared with conventional silicon (Si) and gallium arsenide (GaAs) devices, its GaN-on-SiC RF devices deliver higher breakdown voltage, higher temperature operation, higher efficiency, higher thermal conductivity, higher power density and wider bandwidths, all of which are critical for achieving higher-performing microwave and RF products needed for emerging systems across a variety of applications. In addition to C-band radar power amplifiers, Wolfspeed's GaN-on-SiC RF devices are also enabling next-generation broadband, public safety, and ISM (industrial, scientific & medical) amplifiers; broadcast, satellite, and tactical communications amplifiers; UAV (unmanned aerial vehicle) data links; cellular infrastructure; test instrumentation; and two-way private radios. Read more SAGE Satcom delivers compact, lightweight 12W linear Ka-band GaN block-up converter Semiconductor Today

SAGE SatCom of San Diego, CA, USA (part of telecoms solutions provider REMEC Broadband Wireless), which manufactures power amplifiers for the satellite industry, has added an ultra-compact, efficient, low-power-consumption gallium nitride (GaN)-based 12W linear Ka-band block-up converter (BUC) to its high-transmit-power Ka-band lineup for next-generation satellite data communications. SAGE SatCom says that its GaN solid-state technology allows significant power consumption and size savings compared with widely used

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gallium arsenide (GaAs) technology, without compromising RF performance or reliability. The overall size improvement enables simplified installation directly on the antenna feed arm, without the need for pedestal mounting. SAGE SatCom claims that its Ka-band BUC products offer the highest linear power levels in the most compact and lightweight package on the market. SAGE says that it has deployed many hundreds of its earlier-generation 12W linear Ka-band BUCs in the most demanding customer environments. The new GaN-based 12W linear Ka-band BUC joins its Ka-band portfolio of products, which includes a GaN-based 20W linear Ka-band BUC and a 5W linear Ka-band BUC. Utilizing GaN technology, SAGE has further reduced the size and weight of its 12W linear BUC to a size and power consumption similar to 5W linear Ka-Band BUCs based on GaAs technology. The 12W linear Ka-band BUC measures only 7.5”x5.3”x4” and consumes just 155W at 12W linear output power. “No longer are 1W and 2W transceivers the only options for mission-critical deployments in the Ka-band space,” says Sherman Su, director, global sales. “The SAGE 12W linear power Ka-band BUC is the world's lightest and smallest-form-factor, high-transmit-power BUC and can easily mount on the feed assembly of any Ka-band terminal,” he claims. “Deployments on the edge of a beam, as well as mission-critical applications anywhere in the zone, can be assured of increased transmission qualities with this powerful unit.” “Within the Ka-band space, this new 12W linear unit is also refined for specific use in specialty applications, including Inmarsat's Global Xpress,” Su continues. “In fact, all SAGE products can be engineered for emerging applications. SAGE BUCs exhibit high linear power, have solid-state reliability, consume very little power, are compactly packaged, and extend our lead as the de facto standard for reasonably priced, high-powered amplifiers for the industry's fastest-growing space.” The new SAGE SatCom products is on display on the Sematron stand 1.A78 at IBC in Amsterdam,

The Netherlands (9-13 September) and on the BridgeWave stand A1-32 at GITEX 2016 in Dubai. Read more Consumer electronics chargers to comprise 30% of GaN market in 2022 Semiconductor Today

The launch in late August by Dialog Semiconductor plc - a fabless provider of highly integrated power management, AC/DC power conversion, solid-state lighting (SSL) and Bluetooth low-energy technology - of a gallium nitride (GaN) power IC targeting consumer charger applications adds to the list of recently released GaN devices, which are all power ICs targeting that consumer market segment, forming a trend noted in the report 'Applications & Markets for GaN in Power Electronics' by Point The Power. The first market for GaN in power electronics is consumer power supplies, led by laptop and electronic device chargers, it adds. Consumer electronics chargers could comprise 30% of the GaN market in 2022, it forecasts.

“Consumer systems do not require the same lifetime and warranty as industrial systems,” comments Alex Avron, principal market analyst at Point The Power. “Industry or energy segments like PV [photovoltaic] inverters need a minimum expected lifetime of 10 sometimes 15 years, while the lifetime of a laptop charger is 5 years at most,” he adds. “It's a perfect playground for innovation and new product releases. Many start-ups have

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taken advantage of this, such as California-based companies FinSix and Avogy or Canada-based Appulse Power.” Point The Power notes that the laptop and smartphone charger markets are perfect for testing and trialing wide-bandgap devices and new topologies, due specifically to the comparatively short lifetime required; the fact that size reduction is a main driver; and lower price sensitivity. According to Point The Power, GaN will remain in direct competition with super-junction MOSFETs, which are already the most used devices for consumer power supplies of all kinds – with a total market of more than $800m this year. The market research firm reckons that GaN will enable new applications to emerge for power converters, just as IGBTs and MOSFETs have done in the past; i.e. not replacing bipolar junction transistors (BJTs) but, in fact, facilitating new applications. “Each time a new device has arrived on the market, it did not eat its competing devices' market share, but rather enlarged the overall market size through new applications,” says Avron. According to the report, GaN for consumer power supplies is just the beginning of a bigger trend to offering new, smaller and more efficient charging and powering systems. Read more VisIC launches low-RDS(ON) 650V GaN switch product line in bottom-side-cooled package for switching up to 12A Semiconductor Today

VisIC Technologies Ltd of Nes Ziona, Israel, a fabless developer of power conversion devices based on gallium nitride (GaN) metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) founded in 2010, has launched a new product with an on-resistance (RDS(ON)) rating of just 0.080Ω and a reduced external components requirement using a simplified driving scheme, offered in a smaller package with bottom-side cooling.

The new 650V GaN power switch is a member of the firm's ALL-Switch (Advanced Low Loss Switch) family, designed for bridge converters in motor drives, power supplies, chargers, UPS (uninterruptible power systems), Inverters and other circuits requiring high efficiency and currents up to 12A. VisIC claims that its designs operate with lower gate charge and capacitance than competing products while providing the benefits of low RDS(ON). Offered in low-inductance packaging, the ALL-Switch family is able to deliver high efficiency, adds the firm. For comparison, ALL-Switch's switching losses are 3-5 times lower than comparable silicon carbide (SiC) MOSFET transistors operating at the same frequency, it is reckoned. VisIC says that the V80N65B meets the demand of customers for a bottom-side-cooled package in their designs after they have experienced ALL-Switch's low switching losses. The V80N65B bottom-side-cooled power switch supplements VisIC's existing ALL Switch top-side-cooled product line of 650V GaN devices (the V22N65A, V22S65A and V18G65A). Read more Telcodium Partners with Transphorm to Introduce First-Ever Redundant Power Supplies Using GaN FETs Cantechletter

BOUCHERVILLE, Quebec–(BUSINESS WIRE)–Telcodium, a leader in power supply design, in collaboration with Transphorm Inc. today released the industry’s first redundant power supplies using gallium nitride (GaN) field-effect transistors (FETs). Telcodium’s AC Series replaces a typical three-module power supply architecture (two power supply bricks and one intermediate bus converter (IBC)) with a single power module with redundant AC feeds. Telcodium’s power module operates at 94 percent True System Efficiency (TSE)* or higher—reducing average energy loss by 13 percent or more. To achieve the same TSE with the typical three-module power supply, the bricks

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and IBC would each need to yield a 97 percent efficiency—which exceeds the 80Plus Titanium specification and has yet to be demonstrated by any power supply manufacturer. Further, the new module is 30 percent smaller than the abovementioned two bricks and eliminates the standalone IBC—freeing considerable, critical space inside a host system. The high TSE and size reduction are made possible by Telcodium’s innovative design. This design pairs patented front-end circuitry with the market’s only JEDEC-qualified 650V GaN FET, available from GaN semiconductor design and manufacturing leader Transphorm. The resulting AC Series enables data center, server and telecommunication manufacturers to develop smaller, high-performing systems that can virtually eliminate power supply-related failures. For Series details, see telcodium.com. Highlighted Features and Benefits The following features combined with others not highlighted here can potentially reduce an average system’s total cost of ownership by 19 percent. Feature Benefit Patented front-end circuit design integrated with 650V GaN FETs

Over 94 percent true system efficiency

Over 80 percent standby power reduction (to less than 1W)

Over 30 percent size reduction + standalone IBC elimination

Internal circuitry and system components reduction

Increased airflow

Reduced floor space Increased mean time between failure (MBTF)

Reduced internal system temperature

Increased mean time between failure (MBTF)

Internal supply monitoring (voltage, current and frequency)

Cleanest power selection

Automatic extreme event logging

Supplemental device reduction (e.g., power line monitors)

ORing function elimination

Reduced mechanical parts for greater reliability and reduced maintenance over time

Machine assembly (no hand-soldering)

High-quality assembly Specifications and Availability The AC Series’ universal form factor (260 x 100 x 40mm) is lightweight (1.36 Kg) and fits common equipment developed by data center, server and telecommunications manufacturers. Products are available today and short delivery windows average in-stock to 6 weeks. Read more e2v to supply GaN Systems' 100V and 650V hi-rel GaN transistors to global aerospace & defense industry Semiconductor Today

A master supply agreement has established e2v inc of Milpitas, CA, USA (which provides solutions, sub-systems and components to the medical & science, aerospace & defense and commercial & industrial markets) as the global supplier of 100V and 650V high-reliability GaN transistor products (and customer care) of GaN Systems Inc of Ottawa, Ontario, Canada, a fabless developer of gallium nitride (GaN)-based power switching semiconductors for power conversion and control applications, to the aerospace & defense (A&D) market. e2v will utilize its infrastructure and 30 years of experience in this area to support the hi-rel market with GaN Systems' transistors and evaluation boards. The firm will offer power management solutions that respond directly to the hi-rel market's growing SWaP (size, weight and power) demands. “Our A&D customers must increase system power density, while reducing size and weight,” notes e2v's VP of business development Mont Taylor. “This global partnership with GaN Systems allows us to extend our A&D portfolio and offer new power technologies to meet these requirements,” he adds. “Power designers are routinely reducing the volume and weight of their systems by 4-6 times by using GaN transistors as a replacement for silicon devices,” says GaN Systems' VP of sales &

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marketing Larry Spaziani. “Partnering with e2v enables our solutions to reach, supply and support hundreds of A&D electronic systems designers,” he adds. “e2v's heritage within the A&D market will allow us to extend the availability of our SWaP-conscious power solutions and give our A&D customers the specialist support they deserve.” Read more Mitsubishi Electric expanding Ku-band GaN HEMT range to 70W and 100W to shrink satellite earth stations Semiconductor Today

Tokyo-based Mitsubishi Electric Corp is expanding its lineup of gallium nitride high-electron-mobility transistors (GaN HEMTs) to include models operating at frequencies of 13.75–14.5GHz with saturated output power of 100W (50.0dBm) and 70W (48.3dBm) for use in satellite earth stations utilizing the Ku-band (12-18GHz). Due to optimization of the transistor structure, the new 100W GaN HEMT offers output power that is reckoned to be among the highest available. Shipment of samples will begin on 1 October (70W) and 1 January 2017 (100W). Mitsubishi Electric says that demand for satellite communications is increasing, especially in the Ku-band, which enables high-speed communication even under adverse conditions such as natural disasters and in areas where construction of communication facilities is difficult. Deployment of transmitter equipment using higher-power GaN-HEMTs has become more common in recent years, particularly in high-speed applications such as satellite news gathering.

Picture: Mitsubishi Electric's MGFK50G3745 (left) and MGFK48G3745 (right).

To meet this growing demand for higher output power levels, Mitsubishi Electric is hence expanding its Ku-band GaN-HEMT lineup by introducing the 100W MGFK50G3745 model and 70W MGFK48G3745 model (which both have linear gain of 10.0dB). Mitsubishi Electric notes that, due to the high output power, the need for fewer parts contributes to the miniaturization of transmitter equipment in satellite earth stations. In addition, individual transmitter components can be configured independently during manufacture, eliminating the need for on-site configuration and shortening overall development time. Finally, the existing MGFG5H1503 power amplifier can be used as a driver stage, leveraging the latter's linearizer device to help reduce distortion in power transmitters. Development of the new devices was partially supported by Japan's New Energy and Industrial Technology Development Organization (NEDO). Read more TMD exhibiting GaN-based microwave power module at UAE electronic warfare conference Semiconductor Today

Exhibiting for the first time at an electronic warfare (EW) exhibition in the United Arab Emirates (UAE), on stand 26 at the Electronic Warfare GCC Conference (EW GCC 2016) in Abu Dhabi (25-26 October) UK-based TMD Technologies Ltd (TMD) - which designs and

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manufactures specialized transmitters, amplifiers, microwave power modules (MPMs), high-voltage power supplies and microwave tubes for radar, EW and communications applications - is showcasing a selection of products for electronic warfare. Exhibiting at EW GCC 2016 is “a direct result of our planned on-going expansion into the Middle Eastern markets,” says sales & business development director Jane McAlister. “The EW GCC event is supported by the region's elite intelligence and military community.” The products on show include TMD's newest microwave power modules, namely the recently launched traveling wave tube (TWT)-based PTX8807 and the solid-state PTS6900. Optimized for EW/ECM systems and employing gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) technology, the PTS6900 MPM operates over the 2-6GHz frequency range, with 150W output power and adjustable 55dB gain. The device is said to have a very high predicted mean time between failure (MTBF) for an airborne uninhabited fighter environment. Read more Wolfspeed launches highest-power 50V L-band radar GaN HEMT Semiconductor Today

In booth 156 at European Microwave Week (EuMW 2016) in London, UK (3–7 October), Wolfspeed of Research Triangle Park, NC, USA — a Cree Company that makes gallium nitride on silicon carbide (GaN-on-SiC) high-electron-mobility transistors (HEMTs) and monolithic microwave integrated circuits (MMICs) — is launching what is claimed to be the highest-power 50V GaN HEMT demonstrated to date. Delivering a minimum of 800W of pulsed power at 1.2–1.4GHz and 50V operation with better than 65% drain efficiency, the CGHV14800 features high efficiency, high gain and wide-bandwidth capabilities, making it suitable for L-band radar amplifier applications including air traffic control (ATC) radar, penetration radar, anti-missile system

radar, target-tracking radar, and long-range surveillance radar. Internally matched on input and output, the 900W, 50V GaN HEMT also exhibits 14dB power gain and <0.3dB pulsed amplitude droop. The CGHV14800 is supplied in a ceramic/metal flange package that can be shipped individually, or alongside or installed on a test board. “We demonstrated the CGHV14800 at this year's International Microwave Symposium,” says RF & microwave director Jim Milligan. “Our comprehensive and continually expanding radar product portfolio enables state-of-the-art RF amplifier performance critical for the development of the next-gen defense, aerospace and commercial radar applications,” he claims. Wolfspeed says that, compared with conventional silicon (Si) and gallium arsenide (GaAs) devices, its GaN-on-SiC RF devices deliver higher breakdown voltage, higher-temperature operation, higher efficiency, higher thermal conductivity, higher power density, and wider bandwidths, all of which are critical for achieving smaller, lighter and more efficient microwave and RF products. In addition to L-band radar power amplifiers, the firm's GaN-on-SiC RF devices are also enabling next-generation broadband, public safety, and ISM (industrial, scientific & medical) amplifiers; broadcast, satellite, and tactical communications amplifiers; unmanned aerial vehicle (UAV) data links; cellular infrastructure; test instrumentation; and two-way private radios. Read more VisIC launches 1200V family of GaN power switching devices with integral iso-driver Semiconductor Today

At the IEEE Energy Conversion Congress and Exposition (ECCE2016) in Milwaukie, WI, USA (18-22 September), VisIC Technologies Ltd of Nes Ziona, Israel - a fabless developer of power conversion devices based on gallium nitride (GaN) metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) founded in 2010 - is launching a family of high-voltage GaN devices for switching power electronics designs.

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With a 1200V rating, the GaN modules have typical on-resistance (R DS(ON)) down to just 0.04Ω. Target applications are power converters for motor drives, three-phase power supplies and other applications requiring current switching up to 50A (current limit at the first line of products). The GaN devices are based on VisIC's ALL Switch (Advanced Low Loss Switch) second-generation HEMT technology, which combines high levels of cell integration with optimized cell design, says chief technology officer Gregory Bunin. “This technology supports reduced gate charge and capacitances without losing the benefits of low RDS(ON), with our GaN devices offering an ultra-low maximum switching energy down to 140µJ,” he adds. Switching losses are 3-5 times lower compared to SIC MOSFETs counterparts, it is reckoned. The isolated gate driver is integrated in an isolated DIP power package. The new GaN devices represent high-voltage supplements to VisIC's existing ALL Switch line-up of 650V GaN devices. Read more Unique Driver Architecture Enhances GaN-Based Isolated Power-Supply Designs Power Electronics

GaN-on-silicon E-HEMT transistors are the choice for maximum performance, efficiency and cost-effective power supplies. Cost-effective driver technology enhances supply performance by simplifying layout, reducing component count, and improving reliability. GaN (gallium nitride) E-HEMTs (High Electron Mobility Transistors) have altered the dynamics of power electronics in consumer electronics, datacenters, industrial motors, appliances, and transportation. In the past, the transistor (formerly the Superjunction MOSFET) was the limiting factor in most switching power supplies. For years, 100 kHz-300 kHz was state-of-the-art. Over the last 10 years or so, the only improvements have been confined to efficiency as

MOSFETs have become incrementally better from one generation to the next. With the advent of GaN transistors that look and act like much faster Superjunction MOSFETs, suddenly magnetics, layout techniques, and performance drivers have leapt into the limelight of areas that need to be improved. Driver requirements don’t change much with E-HEMT GaN transistors. But to take full advantage of GaN’s benefits, the few parameters that do change are very important. For instance, GaN Systems Inc. published (Footnote GN001) a simple list of driver requirements that can be used to create the optimal drivers for GaN transistors. Driver requirements for isolated and non-isolated gate drivers include: Minimum Requirements for Non-Isolated Single Gate Driver

Most operate at 5 to 6.5V gate drive

Integrated LDO for regulated 5 to 6V gate drive

ROL≤ 2Ω pull-down output impedance

2A peak drive current

Low-inductance SMT package

<20 ns high-low switch delay match for 100V application

>1MHz switching capability Preferred Requirements for Non-Isolated Single Gate Driver

Separate pull-up/down drive output pins

≤1Ω pull-down impedance

>2A peak drive current for robust turn-off

<20 ns propagation delay Typical Requirements for Isolated Gate Driver

50 to 100kV/ms dv/dt at switching node

50kV/ms Common Mode Transient Immunity (CMTI)

High-low switch delay match: 50 to 100ns for 650V application

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Preferred Requirements for Isolated Gate Driver

>100kV/ms dv/dt at switching node

100 to 200kV/ms CMTI

High-low switch delay match ≤50 ns for 650V application

1. The Bridgeless Totem Pole PFC structure takes advantage of GaN and significantly reduces losses.

Most high-end power supplies in the range from 700W to 3000W and even higher strive to optimize efficiency, cost and power density. This is particularly true for datacenter applications. Most of these power supplies take advantage of GaN in the PFC section, by operating with a front-end consisting of a Bridgeless Totem Pole PFC (Fig. 1). This configuration achieves 28% lower power losses compared to traditional boost PFC circuits. Most switching power supplies use multiple half-bridge circuits, often interleaved for higher power, to create not only the PFC circuit, but often the LLC and other topologies that almost exclusively rely on half-bridge and full bridge circuits. There are several general solutions to driving both the high-side and low-side of the half-bridge, as summarized in Table 1.

Heyday’s HEY1011 integrated solution, shown in Fig. 2, optimizes layout, provides isolation, is cost-effective, and requires no bootstrap circuit or floating power-supply circuit. Used with GaN Systems’ GaN FETs, Heyday’s new line of 650V high-side GaN drivers do not require bootstrap diodes or capacitors and offer superior performance figures compared with other drivers. These drivers exhibit low propagation times of <25ns, and are capable of operating frequencies into the MHz range opening opportunities for systems designers to capture the capabilities of both ever-improving MOS devices and the best GaN devices available.

2. Shown are HE1011 drivers with GaN Systems GS66508 GaN FETs in an H-Bridge configuration.

Restrictions to higher operating frequencies include the drivers and the bootstrap diode. The reverse recovery losses in the diode are a disabler at higher frequencies and start to become prohibitive even at 500 kHz and above. Heyday’s drivers do not need any bootstrap components,

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which enables more efficient drive even in the hundreds of kHz range and into the MHz range. Bootstrap components also suffer from some nasty negative performance anomalies such as bootstrap capacitor “overdrive.” This occurs when the bootstrap capacitor is charged above the intended drive voltage due to negative spikes on the converter switching node. This overcharging can cause the gate of the GaN device to operate outside its specified limits. Heyday’s technology completely alleviates this problem. Figure 3 shows the total propagation from PWM input from controller out to VDRIVE into a 1nF load capacitor of 18ns.

3. Hey1011 propagation delay from PWM input to drive output into 1nF.

Heyday uses a fully integrated magnetic isolation-based transformer to transfer the gate drive signal and the gate drive energy (Fig. 4). So transferring the energy internally in the device importantly eliminates the need for the bootstrap components. These drivers are packaged in fully integrated surface-mount packages.

4. Isolated single HEY1011 driver.

The driver’s capability for operating at higher speed and at low propagation times (<25ns) demonstrates that matching figures part-to-part inherently are excellent. Mismatch figures of <3ns are specified for the Hey1011 650V GaN FET

driver. Using this technique enables the parameters in Table 2 to be met.

The dv/dt immunity figure of the Hey1011 GaN FET driver is >100V/ns. This enables robust fast switching systems, which is very important for GaN-based converters. These drivers also allow for negative voltage swings on the switched reference node of the driver. For example, in the case of a half-bridge technology, if the center switched node swings negative, no problems occur for these drivers. The Hey1011 negative swing limit is as low as -650V. The drivers also deliver bipolar outputs for securely driving the enhancement mode GaN devices into the off state. The Hey1013 delivers gate drive voltages of -2V to +6V.

5. Low- and high-side gate-drive pulses after being “off” for a long duration.

The Hey1021 also can generate a gate-drive voltage of 4.5V to 6V amplitude, all from a single

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+3.3V ground referenced supply. From a single ground-referenced 3.3V supply, the Hey1011 generates a high-side 650V drive with a settable 4.5V to 6V amplitude. Continuous “on” capability is also a useful feature of these drivers. Normally with bootstrap circuits, very long on-times are not possible, as the bootstrap capacitor needs to be topped up. But Heyday drivers have a built-in automatic refresh that can deliver a continuous “on” indefinitely. This can be very useful for automotive applications. “First-pulse-perfect” is an inherent capability of the magnetic coupling technique, the first pulse being the same as all subsequent pulses. Figure 5 shows low- and high-side gate-drive pulses from the Hey1012 in a closed-loop LLC system (VIN = 400V, VOUT = 12V) with an ILOAD step from no-load to 6A. The first driver pulses follow the controller requested pulses perfectly, even after being “off” for a long duration.

6. Hey1011 total driver current with CLOAD of 220pF and 1nF.

In static mode the guaranteed maximum quiescent current on all Heyday driver products is < 400uA. This is very useful for systems that require low standby or sleep-mode power consumption without the need for a sleep pin. Figure 6 shows the current consumption of the Hey1011 GaN driver versus frequency driving a 220pF/1nF load capacitor. Heyday driver devices are sampling now and will be available in fully integrated surface-mount packages in December 2016. The drivers are 2kV,

human-body-model ESD-compliant with die temperature capability of -40°C to 125°C. Read more

OTHER

Riber slashes losses in first-half 2016, driven by 29% growth in MBE system revenue Semiconductor Today

For first-half 2016, Riber S.A. of Bezons, France, which manufactures molecular beam epitaxy (MBE) systems as well as evaporation sources and effusion cells, has confirmed revenue of €6.9m, up 21% on first-half 2015's €5.7m. Growth was driven by all product lines, with MBE systems sales up 29% from €2.8m to €3.6m, sales of services & accessories up 14% from €2.1m to €2.4m, and sales of cells & sources up 25% from €0.8m to €1m. In addition, reflecting the increased sales and the stronger absorption of fixed production costs, Riber has now reported gross margin up from 9% in first-half 2015 to 37% in first-half 2016. Following the roll-out of its savings plan, Riber has cut operating expenditure by 10% year-on-year. Hence, despite continuing to invest (ramping up R&D with a view to developing its range of products and services), net loss has been cut significantly from -€3.5m to -€1.2m. During first-half 2016, cash (net of financial debt) has improved from €0.7m to €0.8m (factoring in the sale of non-strategic real-estate assets for €2.6m at the end of first-half 2016). Furthermore, a capital increase undertaken in August raised €1.4m. Also, the delivery schedule for the end of the year should further strengthen the cash position. As announced on 12 July, orders rose by 40% from €6.3m in first-half 2015 to €8.8m in first-half 2016, comprising five MBE systems (including one production machine) for delivery in 2016

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supplemented by strong growth in sales of components and services. Riber notes that the turnaround is expected to be further strengthened between now and the end of the year. Growth is being supported by sustained development of its range of services and accessories plus concrete progress made with upcoming major contracts. Riber is hence confirming its full-year 2016 revenue target of growth of more than 30%, paving the way for improved net income compared with 2015. Read more

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PATENT APPLICATION

More than 190 new patented inventions were published between 2016-09-02 and 2016-10-01.

Patent Applicants Number of new patent applications

Toshiba 19

Toyoda Gosei 9

Xiangneng Hualei Optoelectronic Corppration 7

LG Innotek 6

Taiyuan University of Technology 6

Mitsubishi Electric 6 Other patent applicants: Stanley Electric, Xiamen Changelight, Sumitomo Electric Industries, Xidian University, Seoul Viosys, Fuji Electric, 13th Research Institute Of China Electronics Technology, IBM, Sharp, Foshan Guoxing Semiconductor Technology, Fujitsu, Sumitomo Chemical, Tokuyama, Electronics & Telecommunications Research Institute (ETRI), Furukawa, Jilin University, Hangzhou Dianzi University, Southeast University (Nanjing China), China Bright Photoelectricity, Osram Opto Semiconductors, University Of Tokyo, Hitachi, 38th Research Institute China Electronics Technology, Institute Of Semiconductors, Epistar, Panasonic, Nippon Telegraph & Telephone (NTT), Infineon Technologies, Indian Institute Of Science, RFHIC, Postech Foundation, Hefei Irico Epilight Technology, Tsinghua University, HC Semitek, Nexdot, Snu R & Db Found, Samsung Electronics, Nichia, Bolb, US Army Research Laboratory, Hexatech, Rohm, Sixpoint Mat, Chonbuk National University Industry Academy Cooperation Foundation, Toyota Central Research & Development Labs, Asahi Chemical Industry, Canon, Robert Bosch, Carnegie Mellon University, Denso, Gigaphoton, Kyushu University, Philips, Institute Of Microelectronics - Chinese Academy Of Sciences, Zhejiang University, Focus Lightings Technology, Jiangsu Jihui New Energy Technology, US Navy, CEA, Hermes Epitek, Freiberger Compound Materials, Toray Industries, Namiki Precision Jewel, Plessey Semiconductors, Changshu Institute Of Technology, Shineon Technology, Dowa Electronics Materials, GaN Systems, Lumistar, Ricoh, Ushio Electric, Soko Kagaku, United Silicon Carbide, Agency For Science Technology & Research (Astar), Air Water, Sony, Enraytek Optoelectronics, China Star Optoelectronics Technology, Yangzhou Zhongke Semiconductor Lighting, Sanan Optoelectronics, Sino Nitride Semiconductor, Hebei University Of Technology, MTEC, Osaka University, Sensor Electronic Technology, Lehigh University, Renesas Electronics, Arkansas Power Electronics Int, Cree, Suzhou Institute Of Nano Technology & Nano Bionics Chinese Academy Of …

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New patent applications selected by Knowmade Devices with semiconductor hyperbolic metamaterials Publication Number: US2016274301 Patent Applicant: US Navy (US)

A hyperbolic metamaterial assembly comprising alternating one or more first layers and one or more second layers forming a hyperbolic metamaterial, the one or more first layers comprising an intrinsic or non-degenerate extrinsic semiconductor and the one or more second layers comprising a two-dimensional electron or hole gas, wherein one of in-plane or out-of-plane permittivity of the hyperbolic metamaterial assembly is negative and the other is positive. Read more Nitride semiconductor device Publication Number: WO2016147541 Patent Applicant: Panasonic (JP)

A nitride semiconductor device (1) is provided with: a substrate (100); an n-type drift layer (102) disposed on the front surface of the substrate (100); a p-type base layer (104) disposed on the drift layer (102); a gate opening

(110), which is formed in the base layer (104), and which reaches the drift layer (102); an n-type channel forming layer (112), which covers the gate opening (110), and which has a channel region; a gate electrode (118) disposed on the channel forming layer (112) in the gate opening (110); an opening (120), which is separated from the gate electrode (118), and which reaches the base layer (104); an opening (122), which is formed in the bottom surface of the opening (120), and which reaches the drift layer (102); a source electrode (124) covering the opening (120) and the opening (122); and a drain electrode (126) disposed on the rear surface of the substrate (100). Read more Nitride semiconductor device and its production method Publication Number: JP2016164926 Patent Applicant: Nippon Telegraph and Telephone Corporation (JP)

PROBLEM TO BE SOLVED: Try to be able to make gate length shorter without decreasing process yield rate. SOLUTION: This nitride semiconductor device is formed from the nitride semiconductor of un dope, being constituted from the channel layer 104 which was formed by the fact that in only the gate territory 121 with respect to insulating layer 103 crystallizes grows, and the nitride semiconductor has with the barrier layer 105 which was formed by the fact that crystallizes grows on only with respect to channel layer 104. Channel layer grain growth (epitaxial growth) does 104 and barrier

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layer 105 when the main surface is designated as III family polarity aspect, when you rephrase, when it is formed by the fact that it crystallizes grows (0001) in surface direction of III family polarity it is good. Read more Packaging solutions for devices and systems comprising lateral gan power transistors Publication Number: US2016268190, US2016268185 Patent Applicant: GaN Systems (CA)

Packaging solutions for devices and systems comprising lateral GaN power transistors are disclosed, including components of a packaging assembly, a semiconductor device structure, and a method of fabrication thereof In the packaging assembly, a GaN die, comprising one or more lateral GaN power transistors, is sandwiched between first and second leadframe layers, and interconnected using low inductance interconnections, without

wirebonding. For thermal dissipation, the dual leadframe package assembly can be configured for either front-side or back-side cooling. Preferred embodiments facilitate alignment and registration of high current/low inductance interconnects for lateral GaN devices, in which contact areas or pads for source, drain and gate contacts are provided on the front-side of the GaN die. By eliminating wirebonding, and using low inductance interconnections with high electrical and thermal conductivity, PQFN technology can be adapted for packaging GaN die comprising one or more lateral GaN power transistors. Read more Embedded gallium-nitride in silicon Publication Number: US2016268475 Patent Applicant: IBM (US)

A method and structure for integrating gallium nitride into a semiconductor substrate. The method may also include means for isolating the gallium nitride from the semiconductor substrate. Read more

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