gan technology for optoelectronics & electronics...application of the nanoporous gan-based tp...
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Coordinated by CRHEA-CNRS research laboratory, this monthly newsletter is produced by Knowmade in collaboration with the managers of GANEXT groups. The newsletter presents a selection of newest scientific publications, patent applications and press releases related to Optoelectronics (LED, micro-LED, laser, photonics, etc.) and Electronics (Power, RF, advanced electronics, etc.) based on III-Nitride semiconductors (GaN, AlN, InN and alloys).
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GANEXT Cluster of Excellence (Labex, 2020-2024) GANEXT is a cluster gathering French research teams involved in GaN technology. The objective of GANEXT is to strengthen the position of French academic players in terms of knowledge and visibility, and reinforce the French industrial players in terms of know-how and market share. GANEXT replaces and succeed GANEX Cluster of Excellence (Labex 2012-2019). www.ganex.fr
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GANEXT Newsletter No. 06 July 2020
GaN Technology for Optoelectronics & Electronics
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IMPORTANT NOTE: The end of GaNeX Cluster of Excellence program (Labex 2012-2019) was scheduled on December 2019. However, the French government decided to expand the labex program for five additional years, in order to further strengthen the synergy between French academic research organizations and industrial players in the field of GaN optoelectronics and electronics. Therefore, GANEXT Cluster of Excellence program will replace and succeed GaNeX for the next five years (2020-2024). Accordingly, the GANEXT newsletter will follow and adapt to the new program, focusing on scientific publications, patent applications and press releases related to optoelectronics (LED, µ-LED, laser, photonics, etc.) and electronics (power, RF, advanced electronics, etc.), ruling out publications which are not related to one of these two families of applications. For instance, publications dealing with MEMS, sensors, photovoltaics, nanostructures, semi-polar and non-polar materials, fundamental physics, etc. that do not obviously relate to optoelectronic or electronic applications will not be included in the GANEXT newsletter. Besides, a panel of GANEXT experts will continue to interact with Knowmade team in order to select the most relevant publications of the month, consistently with GANEXT’s ongoing projects.
TABLE OF CONTENTS
METHODOLOGY ........................................................................................................... 3
SCIENTIFIC PUBLICATIONS............................................................................................ 4
OPTOELECTRONICS ....................................................................................................... 4
ELECTRONICS .............................................................................................................. 20
PRESS RELEASE........................................................................................................... 37
PATENT APPLICATIONS .............................................................................................. 73
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METHODOLOGY
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SCIENTIFIC PUBLICATIONS Selection of new scientific articles
OPTOELECTRONICS Group leader: Bruno Gayral (CEA)
Information selected by Julien Brault (CNRS-CRHEA), Maria Tchernycheva (CNRS-C2N) and Thierry Guillet (CNRS-L2C) Nanoscale Structural and Emission Properties within
“Russian Doll”‐Type InGaN/AlGaN Quantum Wells Canadian Centre for Electron Microscopy and Department
of Materials Science and Engineering, McMaster University,
Main Street West, Hamilton, Ontario, L8S4M1 Canada
Department of Physics, McGill University, 3480 University
Street, Montreal, Quebec, H3A0E9 Canada
Beijing Key Laboratory of Nanophotonics and Ultrafine
Optoelectronic Systems, School of Physics, Beijing Institute
of Technology, 5 Zhongguancun South Street, Beijing,
100081 China
Delmic BV, Kanaalweg 4, Delft, 2628EB The Netherlands
Optic & Electronic Component Material Center, Korea
Institute of Ceramic Engineering & Technology, Jinju, 52851
Republic of Korea
School of Physics and Engineering, Zhengzhou University,
Daxue Road 75, Zhengzhou, 450052 China
Department of Electrical Engineering and Computer
Science, University of Michigan, 1301 Beal Avenue, Ann
Arbor, MI, 48109 USA
Canadian Light Source, 44 Innovation Boulevard, Saskatoon,
Saskatchewan, S7N2V3 Canada
Advanced Optical Materials
https://doi.org/10.1002/adom.202000481
Due to the increasing desire for nanoscale
optoelectronic devices with green light emission
capability and high efficiency, ternary III‐N‐based
nanorods are extensively studied. Many efforts have
been taken on the planar device configuration, which
lead to unavoided defects and strains. With selective‐
area molecular‐beam epitaxy, new “Russian Doll”‐type
InGaN/AlGaN quantum wells (QWs) have been
developed, which could largely alleviate this issue. This
work combines multiple nanoscale characterization
methods and k∙p theory calculations so that the
crystalline structure, chemical compositions, strain
effects, and light emission properties can be
quantitatively correlated and understood. The 3D
structure and atomic composition of these QWs are
retrieved with transmission electron microscopy and
atom probe tomography while their green light
emission has been demonstrated with room‐
temperature cathodoluminescence experiments. k∙p
theory calculations, with the consideration of strain
effects, are used to derive the light emission
characteristics that are compared with the local
measurements. Thus, the structural properties of the
newly designed nanorods are quantitatively
characterized and the relationship with their
outstanding optical properties is described. This
combined approach provides an innovative way for
analyzing nano‐optical‐devices and new strategies for
the structure design of light‐emitting diodes.
Phosphor-free single chip GaN-based white light
emitting diodes with a moderate color rendering
index and significantly enhanced communications
bandwidth State Key Laboratory of High Performance Complex
Manufacturing, College of Mechanical and Electrical
Engineering, Central South University, Changsha 410083,
China
Semiconductor Lighting Technology Research and
Development Center, Institute of Semiconductors, Chinese
Academy of Sciences, Beijing 100083, China
College of Materials Science and Opto-Electronic
Technology, University of Chinese Academy of Sciences,
Beijing 101408, China
State Key Laboratory of Integrated Optoelectronics,
Institute of Semiconductors, Chinese Academy of Sciences,
Beijing 100083, China
Photonics Research
https://doi.org/10.1364/PRJ.392046
To achieve high quality lighting and visible light
communication (VLC) simultaneously, GaN based
white light emitting diodes (WLEDs) oriented for
lighting in VLC has attracted great interest. However,
the overall bandwidth of conventional phosphor
converted WLEDs is limited by the long lifetime of
phosphor, the slow Stokes transfer process, the
resistance-capacitance (RC) time delay, and the
quantum-confined Stark effect (QCSE). Here by
adopting a self-assembled InGaN quantum dots (QDs)
structure, we have fabricated phosphor-free single
https://doi.org/10.1002/adom.202000481https://doi.org/10.1364/PRJ.392046
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chip WLEDs with tunable correlated color temperature
(CCT, from 1600 K to 6000 K), a broadband spectrum,
a moderate color rendering index (CRI) of 75, and a
significantly improved modulation bandwidth
(maximum of 150 MHz) at a low current density of
72 A/cm2. The broadband spectrum and high
modulation bandwidth are ascribed to the capture of
carriers by different localized states of InGaN QDs with
alleviative QCSE as compared to the traditional
InGaN/GaN quantum well (QW) structures. We
believe the approach reported in this work will find its
potential application in GaN WLEDs and advance the
development of semiconductor lighting-
communication integration.
Tamm plasmons in metal/nanoporous GaN
distributed Bragg reflector cavities for active and
passive optoelectronics Materials Department, University of California Santa
Barbara, Santa Barbara, California 93106, USA
Solid-State Lighting Energy Electronic Center (SSLEEC),
University of California Santa Barbara, Santa Barbara,
California 93106, USA
Department of Physics, University of California Santa
Barbara, Santa Barbara, California 93106, USA
Université Lyon, Université Claude Bernard Lyon 1, CNRS,
Institut Lumière Matière, F-69622 Lyon, France
Optics Express
https://doi.org/10.1364/OE.392546
We theoretically and experimentally investigate
Tamm plasmon (TP) modes in a metal/semiconductor
distributed Bragg reflector (DBR) interface. A thin Ag
(silver) layer with a thickness (55 nm from simulation)
that is optimized to guarantee a low reflectivity at the
resonance was deposited on nanoporous GaN DBRs
fabricated using electrochemical (EC) etching on
freestanding semipolar GaN substrates. The
reflectivity spectra of the DBRs are compared before
and after the Ag deposition and with that of a blanket
Ag layer deposited on GaN. The experimental results
indicate the presence of a TP mode at ∼ 454 nm on
the structure after the Ag deposition, which is also
supported by theoretical calculations using a transfer-
matrix algorithm. The results from mode dispersion
with energy-momentum reflectance spectroscopy
measurements also support the presence of a TP
mode at the metal-nanoporous GaN DBR interface. An
active medium can also be accommodated within the
mode for optoelectronics and photonics. Moreover,
the simulation results predict a sensitivity of the TP
mode wavelength to the ambient (∼ 4-7 nm shift
when changing the ambient within the pores from air
with n = 1 to isopropanol n = 1.3), suggesting an
application of the nanoporous GaN-based TP structure
for optical sensing.
Three-dimensional metal–semiconductor–metal AlN
deep-ultraviolet detector State Key Laboratory of High-Performance Complex
Manufacturing, College of Mechanical and Electrical
Engineering, Central South University, Changsha, Hunan
410083, China
Key Laboratory of Hunan Province for Efficient Power
System and Intelligent Manufacturing, Shaoyang University,
Shaoyang, Hunan 422000, China
Research and Development Center for Solid State Lighting,
Institute of Semiconductors, Chinese Academy of Sciences,
Beijing 100083, China
Hunan Key Laboratory of Super-microstructure and
Ultrafast Process, School of Physics and Electronics, Central
South University, Hunan 410083, China
Optics Letters
https://doi.org/10.1364/OL.394338
Conventional metal–semiconductor–metal (MSM)
ultraviolet (UV) detectors have the disadvantage of
limited adjustable structural parameters, finite
electrical field, and long carrier path. In this Letter, we
demonstrate a three-dimensional (3D) MSM structural
AlN-based deep-UV (DUV) detector, fabricated
through simple trench etching and metal deposition,
while flip bonding to the silicon substrate forms a flip-
chip 3D-MSM (FC-3DMSM) device. 3D-MSM devices
exhibit improved responsiveness and response speed,
compared with conventional MSM devices. Time-
dependent photoresponse of all devices is also
investigated here. The enhanced performance of the
3D-MSM device is to be attributed to the intensified
electrical field from the 3D metal electrode
configuration and the inhibition of the carrier vertical
transport, which unambiguously increases the carrier
collection efficiency and migration speed, and thus the
responsivity and speed as well. This work should
advance the design and fabrication of AlN-based DUV
detectors.
https://doi.org/10.1364/OE.392546https://doi.org/10.1364/OL.394338
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560 nm InGaN micro-LEDs on low-defect-density and
scalable (20-21) semipolar GaN on patterned
sapphire substrates Materials Department, University of California Santa
Barbara, Santa Barbara, CA 93117, USA
Department of Electrical and Computer Engineering,
University of California Santa Barbara, CA 93117, USA
Department of Electrical and Computer Engineering,
University of Yale, CT 06520, USA
Optics Express
https://doi.org/10.1364/OE.387561
We demonstrate InGaN-based semipolar 560 nm
micro-light-emitting diodes with 2.5% EQE on high-
quality and low-defect-density (20-21) GaN templates
grown on scalable and low-cost sapphire substrates.
Through transmission electron microscopy
observations, we discuss how the management of
misfit dislocations and their confinement in areas
away from the active light-emitting region is necessary
for improving device performance. We also discuss
how the patterning of semipolar GaN on sapphire
influences material properties in terms of surface
roughness and undesired faceting in addition to
indium segregation at the proximity of defected areas.
Improving carrier transport in AlGaN deep-ultraviolet
light-emitting diodes using a strip-in-a-barrier
structure Department of Electrical and Computer Engineering, New
Jersey Institute of Technology, 323 Dr. Martin Luther King
Jr. Boulevard, Newark, New Jersey 07102, USA
Institute of Chemical Technology, Vietnam Academy of
Science and Technology, Ho Chi Minh City 700000, Vietnam
Department of Electronics and Communication
Engineering, National Institute of Technology Silchar, Assam
788010, India
Applied Optics
https://doi.org/10.1364/AO.394149
This paper reports the illustration of electron blocking
layer (EBL)-free AlGaN light-emitting diodes (LEDs)
operating in the deep-ultraviolet (DUV) wavelength at
∼270nm. In this work, we demonstrated that the
integration of an optimized thin undoped AlGaN strip
layer in the middle of the last quantum barrier (LQB)
could generate enough conduction band barrier
height for the effectively reduced electron overflow
into the 𝑝-GaN region. Moreover, the hole injection
into the multi-quantum-well active region is
significantly increased due to a large hole
accumulation at the interface of the AlGaN strip and
the LQB. As a result, the internal quantum efficiency
and output power of the proposed LED structure has
been enhanced tremendously compared to that of the
conventional 𝑝-type EBL-based LED structure.
Modelling and optical response of a compressive-
strained AlGaN/GaN quantum well laser diode Laboratory of Metallic and Semiconducting Materials
(LMSM), Department of Electrical Engineering, Biskra
University, Biskra, Algeria
Faculty of Science, Elhadj Lakhdar University, Batnal, Algeria
Research Centre in Industrial Technology (CRTI), Algiers,
Algeria
DIIES – Mediterranea University of Reggio Calabria, Reggio
Calabria, Italy
Journal of Semiconductors
https://doi.org/10.1088/1674-4926/41/6/062301
The effects of the quantum well (QW) width, carrier
density, and aluminium (Al) concentration in the
barrier layers on the optical characteristics of a gallium
nitride (GaN)-based QW laser diode are investigated
by means of a careful modelling analysis in a wide
range of temperatures. The device's optical gain is
calculated by using two different band energy models.
The first is based on the simple band-to-band model
that accounts for carrier transitions between the first
levels of the conduction band and valence band,
whereas the second assumes the perturbation theory
(k.p model) for considering the valence intersubband
transitions and the relative absorption losses in the
QW. The results reveal that the optical gain increases
with increasing the n-type doping density as well as
the Al molar fraction of the AlxGa1–xN layers, which
originate the GaN compressive-strained QW. In
particular, a significant optical gain on the order of
5000 cm–1 is calculated for a QW width of 40 Å at
room temperature. In addition, the laser threshold
current density is of few tens of A/cm2 at low
temperatures.
https://doi.org/10.1364/OE.387561https://doi.org/10.1364/AO.394149https://doi.org/10.1088/1674-4926/41/6/062301
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Size-independent low voltage of InGaN micro-light-
emitting diodes with epitaxial tunnel junctions using
selective area growth by metalorganic chemical
vapor deposition Materials Department, University of California, Santa
Barbara, CA 93106, USA
Department of Electrical and Computer Engineering,
University of California, Santa Barbara, CA 93106, USA
Optics Express
https://doi.org/10.1364/OE.394664
High performance InGaN micro-size light-emitting
diodes (µLEDs) with epitaxial tunnel junctions (TJs)
were successfully demonstrated using selective area
growth (SAG) by metalorganic chemical vapor
deposition (MOCVD). Patterned n + GaN/n-GaN layers
with small holes were grown on top of standard InGaN
blue LEDs to form TJs using SAG. TJ µLEDs with squared
mesa ranging from 10×10 to 100×100 µm2 were
fabricated. The forward voltage (Vf) in the reference
TJ µLEDs without SAG is very high and decreases
linearly from 4.6 to 3.7 V at 20 A/cm2 with reduction
in area from 10000 to 100 µm2, which is caused by the
lateral out diffusion of hydrogen through sidewall. By
contrast, the Vf at 20 A/cm2 in the TJ µLEDs utilizing
SAG is significantly reduced to be 3.24 to 3.31 V.
Moreover, the Vf in the SAG TJ µLEDs is independent
on sizes, suggesting that the hydrogen is effectively
removed through the holes on top of the p-GaN
surface by SAG. The output power of SAG TJ µLEDs is
∼10% higher than the common µLEDs with indium tin
oxide (ITO) contact.
Enhanced wall plug efficiency of AlGaN-based deep-
UV LEDs using Mo/Al as p-contact Ferdinand-Braun-Institut, Leibniz-Institut für
Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489
Berlin, Germany
Institute of Solid State Physics, Hardenbergstr. 36, EW 6-1,
10623 Berlin, Germany
IEEE Photonics Technology Letters
https://doi.org/10.1109/LPT.2020.3003164
P-type contacts with a high reflectivity in the
ultraviolet spectral region made of
molybdenum/aluminum (Mo/Al) on AlGaN-based
deep-ultraviolet light-emitting diodes (DUV LEDs)
emitting at 265 nm have been investigated. Optimized
Mo/Al contacts are shown to have a high optical
reflectivity above 75 % at 265 nm. DUV LEDs with an
absorbing p-AlGaN heterostructure operated at 20 mA
show a 15 % higher light output power and a 1 V lower
voltage when Mo/Al instead of Pt is used as p-contact.
The effect on the voltage of DUV LEDs with a UV-
transparent p-side heterostructure is similar.
Moreover, DUV LEDs with a Mo/Al contact show a
lower operation voltage compared to LEDs with an
indium tin oxide/aluminum (ITO/Al) p-contact where
the ITO is intended to form a semitransparent low-
resistance contact and the Al serves as a reflector.
Implementation of the inductively coupled plasma
etching processes for forming gallium nitride
nanorods used in ultraviolet light-emitting diode
technology Łukasiewicz Research Network-Institute of Electron
Technology, Al.Lotników 32/46, 02-668 Warsaw, Poland
Institute of Physics, Silesian University of Technology, ul.
Konarskiego 22B, 44-100 Gliwice, Poland
Warsaw University of Technology, Institute of
Microelectronics and Optoelectronics, ul. Koszykowa 75,
00-662 Warsaw, Poland
Journal of Vacuum Science & Technology B
https://doi.org/10.1116/6.0000133
This report presents the results of fabricating GaN
nanorods by inductively coupled plasma etching using
BCl3/Cl2 chemistry. Interestingly, the GaN nanorods
are formed only in the area initially masked by the
sacrificial metal mask. In addition to the metallic mask,
a specific feature of this process is the application of
an insulating ceramic carrier for the improvement of
the process performance. The authors show that using
the same etching parameters but with a conductive
silicon carrier significantly reduces the efficiency of
nanorod formation. Auger electron spectroscopy was
applied to propose and confirm the mechanism of
nanorod formation ceramic carrier and properly
selected metallic masks. The usefulness of the
developed method of nanorod production has been
confirmed by its application in the fabrication and
characterization of GaN-based UV light-emitting
diodes.
https://doi.org/10.1364/OE.394664https://doi.org/10.1109/LPT.2020.3003164https://doi.org/10.1116/6.0000133
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Impact of defects on Auger recombination in c-plane
InGaN/GaN single quantum well in the efficiency
droop regime Institute of Physics, École Polytechnique Fédérale de
Lausanne (EPFL), CH-1015 Lausanne, Switzerland
Applied Physics Letters
https://doi.org/10.1063/5.0004321
We study the impact of non-radiative defects on Auger
recombination in c-plane InGaN/GaN single quantum
wells (SQWs) in the efficiency droop regime using high
injection time-resolved photoluminescence. The
defect density in the SQW is controlled by tuning the
thickness of an InAlN underlayer. When the defect
density is increased, apart from Shockley–Read–Hall
(SRH) and standard Auger recombination, introducing
an extra defect-assisted Auger process is required to
reconcile the discrepancy observed between the usual
ABC model and experimental data. We derive a linear
dependence between the SRH coefficient and the
bimolecular defect-assisted Auger coefficient, which
suggests that the generated defects can act as
scattering centers responsible for indirect Auger
processes. In particular, in defective SQWs, the defect-
assisted Auger recombination rate can exceed the
radiative one. Our results further suggest that the
defect-assisted Auger recombination is expected to be
all the more critical in green to red III-nitride light-
emitting diodes due to their reduced radiative rate.
Thermal droop in III-nitride based light-emitting
diodes: Physical origin and perspectives Department of Information Engineering, University of
Padova, via Gradenigo 6/b, 35131 Padova, Italy
Department of Electronics and Telecommunications,
Politecnico di Torino, corso Duca degli Abruzzi 24, 10129
Turin, Italy
Consiglio Nazionale delle Ricerche (CNR), Istituto di
Elettronica e di Ingegneria dell'Informazione e delle
Telecomunicazioni (IEIIT), corso Duca degli Abruzzi 24,
10129 Turin, Italy
Journal of Applied Physics
https://doi.org/10.1063/5.0005874
This tutorial paper focuses on the physical origin of
thermal droop, i.e., the decrease in the luminescence
of light-emitting diodes (LEDs) induced by increasing
temperature. III-nitride-based LEDs are becoming a
pervasive technology, covering several fields from
lighting to displays, from automotive to portable
electronics, and from horticulture to sensing. In all
these environments, high efficiency is a fundamental
requirement, for reducing power consumption and
system cost. Over the last decade, a great deal of
effort has been put in the analysis of the efficiency
droop, the decrease in LED internal quantum
efficiency (IQE) induced by high current density. On
the other hand, an IQE decrease is observed also for
increasing temperature, a phenomenon usually
referred to as thermal droop. For commercial LEDs,
the IQE decrease related to thermal droop can be
comparable to that of efficiency droop: for this reason,
understanding thermal droop is a fundamental step
for making LEDs capable of operating at high
temperature levels. In several fields (including street
lighting, automotive, photochemical treatments,
projection, entertainment lighting, etc.), compact and
high-flux light sources are required: typically, to
reduce the size, weight, and cost of the systems, LEDs
are mounted in compact arrays, and heat sinks are
reduced to a minimum. As a consequence, LEDs can
easily reach junction temperatures above 85–100 °C
and are rated for junction temperatures up to 150–
175 °C (figures from commercially available LED
datasheets: Cree XHP70, Osram LUW HWQP, Nichia
NVSL219CT, Samsung LH351B, and LedEngin LZP-
00CW0R) and this motivates a careful analysis of
thermal droop. This paper discusses the possible
physical causes of thermal droop. After an
introduction on the loss mechanisms in junctions, we
will individually focus on the following processes: (i)
Shockley–Read–Hall (SRH) recombination and
properties of the related defects; (ii) Auger
recombination and its temperature dependence,
including the discussion of trap-assisted Auger
recombination; (iii) impact of carrier transport on the
thermal droop, including a discussion on carrier
delocalization, escape, and freeze out; (iv) non-SRH
defect-related droop mechanisms. In addition, (v) we
discuss the processes that contribute to light emission
at extremely low current levels and (vi) the thermal
droop in deep ultraviolet LEDs, also with reference to
the main parasitic emission bands. The results
presented within this paper give a tutorial perspective
on thermal droop; in addition, they suggest a pathway
for the mitigation of this process and for the
https://doi.org/10.1063/5.0004321https://doi.org/10.1063/5.0005874
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development of LEDs with stable optical output over a
broad temperature range.
Lasing up to 380 K in a sublimated GaN nanowire Nanophotonics Center, NTT Corp., 3-1, Morinosato
Wakamiya Atsugi, Kanagawa 243-0198, Japan
NTT Basic Research Laboratories, NTT Corp., 3-1,
Morinosato Wakamiya Atsugi, Kanagawa 243-0198, Japan
Université Côte d'Azur, CNRS, CRHEA, Rue B. Grégory,
06560 Valbonne, France
NTT Device Technology Laboratory, NTT Corp., 3-1,
Morinosato Wakamiya Atsugi, Kanagawa 243-0198, Japan
Applied Physics Letters
https://doi.org/10.1063/5.0004771
We report on GaN nanowire lasers fabricated by
selective-area sublimation, and we show that
sublimated GaN nanowires can exhibit ultraviolet
lasing action under optical pumping beyond room
temperature, up to 380 K. We study by
microphotoluminescence the temperature-
dependent behavior of single nanowire lasers
between 7 K and 380 K and extract a characteristic
temperature of T = 126 K. We finally present a
statistical study of the maximum lasing temperature in
individual sublimated GaN nanowires and use it to
assess the performance of the selective-area
sublimation method for nanowire-based lasing
applications.
Au-Nanoplasmonics-Mediated Surface Plasmon-
Enhanced GaN Nanostructured UV Photodetectors Department of Electronics and Communication
Engineering, Delhi Technological University, New Delhi
110042, India
CSIR-National Physical Laboratory, Dr. K.S. Krishnan Road,
New Delhi 110012, India
Academy of Scientific and Innovative Research, CSIR-HRDC
Campus, Ghaziabad, Uttar Pradesh 201002, India
ACS Omega
https://doi.org/10.1021/acsomega.0c01239
The nanoplasmonic impact of chemically synthesized
Au nanoparticles (Au NPs) on the performance of GaN
nanostructure-based ultraviolet (UV) photodetectors
is analyzed. The devices with uniformly distributed Au
NPs on GaN nanostructures (nanoislands and
nanoflowers) prominently respond toward UV
illumination (325 nm) in both self-powered as well as
photoconductive modes of operation and have shown
fast and stable time-correlated response with
significant enhancement in the performance
parameters. A comprehensive analysis of the device
design, laser power, and bias-dependent responsivity
and response time is presented. The fabricated Au
NP/GaN nanoflower-based device yields the highest
photoresponsivity of ∼ 380 mA/W, detectivity of ∼
1010 jones, reduced noise equivalent power of ∼ 5.5
× 10–13 W Hz–1/2, quantum efficiency of ∼ 145%, and
fast response/recovery time of ∼40 ms. The report
illustrates the mechanism where light interacts with
the chemically synthesized nanoparticles guided by
the surface plasmon to effectively enhance the device
performance. It is observed that the Au NP-stimulated
local surface plasmon resonance effect and reduced
channel resistance contribute to the augmented
performance of the devices. Further, the decoration of
low-dimensional Au NPs on GaN nanostructures acts
as a detection enhancer with a fast recovery time and
paves the way toward the realization of energy-
efficient optoelectronic device applications.
Demonstration of efficient semipolar 410 nm violet
laser diodes heteroepitaxially grown on high-quality
low-cost GaN/sapphire substrates Materials Department, University of California, Santa
Barbara, CA 93106, USA
Department of Electrical and Computer Engineering,
University of California, Santa Barbara, CA 93106, USA
ACS Appl. Electron. Mater.
https://doi.org/10.1021/acsaelm.0c00364
Heteroepitaxial growth of semipolar laser diodes (LDs)
on foreign substrate is extremely challenging but
crucial to reduce the cost of semipolar bulk GaN
substrates. In this work, we demonstrate the first
efficient semipolar 410 nm violet LDs grown on high-
quality low-cost semipolar GaN/sapphire substrates.
The fabricated semipolar LD exhibits a high output
power of more than 900 mW at 1.6 A, and a wall-plug
efficiency of 5.6% under pulsed operation. The
analysis also quantitatively confirms that the high
density of defects and high non-radiative
recombination rate in the active region account for the
high transparency current observed in the devices.
https://doi.org/10.1063/5.0004771https://doi.org/10.1021/acsomega.0c01239https://doi.org/10.1021/acsaelm.0c00364
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RGB arrays for micro-LED applications using
nanoporous GaN embedded with quantum dots Department of Electrical Engineering, Yale University, New
Haven 06520, United States
Department of Chemical and Environmental Engineering,
Yale University, New Haven 06520, United States
Energy Sciences Institute, Yale University, West Haven
06516, United States
Department of Physics, Chonnam National University,
Gwangju 61186, Republic of Korea
Electronic and Optoelectronic System Research
Laboratories, Industrial Technology Research Institute ITRI,
Hsinchu, Taiwan
ACS Appl. Mater. Interfaces
https://doi.org/10.1021/acsami.0c00839
The multiple light scattering of nanoporous (NP) GaN
was systematically studied and applied to the color
down-conversion for micro-LED display applications.
The transport mean free path (TMFP) in NP GaN is 660
nm at 450 nm (light wavelength) and it decreases with
decreasing wavelength. It was observed that the short
TMFP of the NP GaN increased the light extinction
coefficient at 370 nm by 11 times. Colloidal QDs were
loaded into half 4” wafer-scale NP GaN, and 96 and
100% light conversion efficiencies for green and red
were achieved, respectively. By loading green and red
QDs selectively into NP GaN mesas, we demonstrated
the RGB micro-arrays based on the blue-violet
pumping light with green and red color converting
regions.
Reversing abnormal hole localization in high-Al-
content AlGaN quantum well to enhance deep
ultraviolet emission by regulating the orbital state
coupling Engineering Research Center of Micro-nano Optoelectronic
Materials and Devices, Ministry of Education; Fujian
Provincial Key Laboratory of Semiconductor Materials and
Applications; Collaborative Innovation Center for
Optoelectronic Semiconductors and Efficient Devices;
Department of Physics, Xiamen University, 361005 Xiamen,
China
Light: Science & Applications
https://doi.org/10.1038/s41377-020-00342-3
AlGaN has attracted considerable interest for
ultraviolet (UV) applications. With the development of
UV optoelectronic devices, abnormal carrier
confinement behaviour has been observed for c-
plane-oriented AlGaN quantum wells (QWs) with high
Al content. Because of the dispersive crystal field split-
off hole band (CH band) composed of pz orbitals, the
abnormal confinement becomes the limiting factor for
efficient UV light emission. This observation differs
from the widely accepted concept that confinement of
carriers at the lowest quantum level is more
pronounced than that at higher quantum levels, which
has been an established conclusion for conventional
continuous potential wells. In particular, orientational
pz orbitals are sensitive to the confinement direction
in line with the conducting direction, which affects the
orbital intercoupling. In this work, models of
Al0.75Ga0.25N/AlN QWs constructed with variable
lattice orientations were used to investigate the
orbital intercoupling among atoms between the well
and barrier regions. Orbital engineering of QWs was
implemented by changing the orbital state
confinement, with the well plane inclined from 0° to
90° at a step of 30° (referred to the c plane). The
barrier potential and transition rate at the band edge
were enhanced through this orbital engineering. The
concept of orbital engineering was also demonstrated
through the construction of inclined QW planes on
semi- and nonpolar planes implemented in microrods
with pyramid-shaped tops. The higher emission
intensity from the QWs on the nonpolar plane
compared with those on the polar plane was
confirmed via localized cathodoluminescence (CL)
maps.
Mini-LED, Micro-LED and OLED displays: present
status and future perspectives College of Optics and Photonics, University of Central
Florida, Orlando, FL, 32816, USA
Light: Science & Applications
https://doi.org/10.1038/s41377-020-0341-9
Presently, liquid crystal displays (LCDs) and organic
light-emitting diode (OLED) displays are two dominant
flat panel display technologies. Recently, inorganic
mini-LEDs (mLEDs) and micro-LEDs (μLEDs) have
emerged by significantly enhancing the dynamic range
of LCDs or as sunlight readable emissive displays.
“mLED, OLED, or μLED: who wins?” is a heated
debatable question. In this review, we conduct a
https://doi.org/10.1021/acsami.0c00839https://doi.org/10.1038/s41377-020-00342-3https://doi.org/10.1038/s41377-020-0341-9
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comprehensive analysis on the material properties,
device structures, and performance of
mLED/μLED/OLED emissive displays and mLED backlit
LCDs. We evaluate the power consumption and
ambient contrast ratio of each display in depth and
systematically compare the motion picture response
time, dynamic range, and adaptability to
flexible/transparent displays. The pros and cons of
mLED, OLED, and μLED displays are analysed, and their
future perspectives are discussed.
External Quantum Efficiency of 6.5% at 300nm
emission and 4.7% at 310nm emission on bare-wafer
of AlGaN-based UVB LEDs RIKEN Cluster for Pioneering Research (CPR), 2-1 Hirosawa,
Wako, Saitama 351-0198, Japan
RIKEN Center for Advanced Photonics (RAP), 2-1 Hirosawa,
Wako, Saitama 351-0198, Japan
Yamaguchi University, 2-16-1 Tokiwadai, Ube Yamaguchi
755-8611, Japan
ACS Appl. Electron. Mater.
https://doi.org/10.1021/acsaelm.0c00172
By the Minamata Convention on Mercury, regulation
on Mercury use will be stricter from this year of 2020
and safe AlGaN-based ultraviolet (UV) light sources are
urgently needed for killing of SARS-CoV-2 (corona
virus). AlGaN-based ultraviolet‐B (UVB) light‐emitting
diodes (LEDs) and UVB laser diodes (LDs) have the
potential to replace toxic mercury UV-Lamps.
Previously, the internal-quantum-efficiency (ηint)
were enhanced from 47% to 54% in AlGaN UVB multi-
quantum-well (MQWs). However, some non-linear
behavior in both light output power (L) and external-
quantum-efficiency (ηext) in the 310nm-band UVB
LEDs were observed and later on such nonlinearities
were overcome by reducing the thicknesses of
quantum-well-barriers (TQWB) in MQWs. After
relaxing to the n-AlGaN electron injection layer (EIL)
up to 50% underneath the MQWs and using highly
reflective Ni/Al p-electrode, the L and ηext,
respectively, of 310nm-band UVB LED were greatly
improved from 12 mW and 2.3% to a record value of
29 mW and 4.7%. Similarly, for 294nm-band UVB LED,
the ηext and L, respectively, were also remarkably
improved up to 6.5% and 32 mW at RT on bare-wafer
condition, using better carrier confinement scheme in
the MQWs as well as using moderately Mg-doped p-
type multi-quantum-barrier electron-blocking-layer
(p-MQB EBL). Moderately doped p-MQB EBL was
aimed for better hole transport to enhance the hole
injection toward the MQWs as well as to block the high
energy electron from overshooting. Possible
explanations and recommendations for the
improvements in the performances of 294-310nm
UVB LEDs are broadly discussed. Most importantly,
such controllable multi UVB-wavelength emitters may
extend nitride‐based LEDs to previously inaccessible
areas, for example, electrically pumped AlGaN-based
UVB LDs.
Unidirectional luminescence from InGaN/GaN
quantum-well metasurfaces Department of Electrical and Computer Engineering,
University of California Santa Barbara, Santa Barbara, CA,
USA
Department of Physics, University of California Santa
Barbara, Santa Barbara, CA, USA
Department of Material Science and Engineering, University
of California Santa Barbara, Santa Barbara, CA, USA
Solid State Lighting and Energy Electronics Center,
University of California Santa Barbara, Santa Barbara, CA,
USA
Nature Photonics
https://doi.org/10.1038/s41566-020-0641-x
III–nitride light-emitting diodes (LEDs) are the
backbone of ubiquitous lighting and display
applications. Imparting directional emission is an
essential requirement for many LED implementations.
Although optical packaging1, nanopatterning2,3 and
surface roughening4 techniques can enhance LED
extraction, directing the emitted light requires bulky
optical components. Optical metasurfaces provide
precise control over transmitted and reflected
waveforms, suggesting a new route for directing light
emission. However, it is difficult to adapt metasurface
concepts for incoherent light emission, due to the lack
of a phase-locking incident wave. Here, we
demonstrate a metasurface-based design of
InGaN/GaN quantum-well structures that generate
narrow, unidirectional transmission and emission
lobes at arbitrary engineered angles. We further
demonstrate 7-fold and 100-fold enhancements of
total and air-coupled external quantum efficiencies,
respectively. The results present a new strategy for
https://doi.org/10.1021/acsaelm.0c00172https://doi.org/10.1038/s41566-020-0641-x
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exploiting metasurface functionality in light-emitting
devices.
Quasi‐2D Growth of Aluminum Nitride Film on
Graphene for Boosting Deep Ultraviolet Light‐
Emitting Diodes Research and Development Center for Semiconductor
Lighting Technology, Institute of Semiconductors, Chinese
Academy of Sciences, Beijing, 100083 China
Center of Materials Science and Optoelectronics
Engineering, University of Chinese Academy of Sciences,
Beijing, 100049 China
Beijing Graphene Institute (BGI), Beijing, 100095 China
Center for Nanochemistry (CNC), Beijing Science and
Engineering Center for Nanocarbons, College of Chemistry
and Molecular Engineering, Peking University, Beijing,
100871 China
Electron Microscopy Laboratory, and International Center
for Quantum Materials, School of Physics, Peking University,
Beijing, 100871 China
State Key Laboratory of Superlattices and Microstructures,
Institute of Semiconductors, Chinese Academy of Sciences,
Beijing, 100083 China
Center of Materials Science and Optoelectronics
Engineering, University of Chinese Academy of Sciences,
Beijing, 100049 China
School of Electronics and Information Engineering, Hebei
University of Technology, Tianjin, 300401 China
Research and Development Center for Semiconductor
Lighting Technology, Institute of Semiconductors, Chinese
Academy of Sciences, Beijing, 100083 China
Collaborative Innovation Center of Quantum Matter,
Beijing, 100871 China
Advanced Science
https://doi.org/10.1002/advs.202001272
Efficient and low‐cost production of high‐quality
aluminum nitride (AlN) films during heteroepitaxy is
the key for the development of deep ultraviolet light‐
emitting diodes (DUV‐LEDs). Here, the quasi‐2D
growth of high‐quality AlN film with low strain and low
dislocation density on graphene (Gr) is presented and
a high‐performance 272 nm DUV‐LED is
demonstrated. Guided by first‐principles calculations,
it is found that AlN grown on Gr prefers lateral growth
both energetically and kinetically, thereby resulting in
a Gr‐driven quasi‐2D growth mode. The strong lateral
growth mode enables most of dislocations to
annihilate each other at the AlN/Gr interface, and
therefore the AlN epilayer can quickly coalesce and
flatten the nanopatterned sapphire substrate. Based
on the high quality and low strain of AlN film grown on
Gr, the as‐fabricated 272 nm DUV‐LED shows a 22%
enhancement of output power than that with low‐
temperature AlN buffer, following a negligible
wavelength shift under high current. This facile
strategy opens a pathway to drastically improve the
performance of DUV‐LEDs.
Dislocation‐Free and Atomically Flat GaN Hexagonal
Microprisms for Device Applications Solid State Physics and NanoLund, Lund University, Box 118,
Lund, 221 00 Sweden
nCHREM/Centre for Analysis and Synthesis and NanoLund,
Lund University, Box 124, Lund, 221 00 Sweden
Synchrotron Radiation Research and NanoLund, Lund
University, Box 118, Lund, 221 00 Sweden
small
https://doi.org/10.1002/smll.201907364
III‐nitrides are considered the material of choice for
light‐emitting diodes (LEDs) and lasers in the visible to
ultraviolet spectral range. The development is
hampered by lattice and thermal mismatch between
the nitride layers and the growth substrate leading to
high dislocation densities. In order to overcome the
issue, efforts have gone into selected area growth of
nanowires (NWs), using their small footprint in the
substrate to grow virtually dislocation‐free material.
Their geometry is defined by six tall side‐facets and a
pointed tip which limits the design of optoelectronic
devices. Growth of dislocation‐free and atomically
smooth 3D hexagonal GaN micro‐prisms with a flat,
micrometer‐sized top‐surface is presented. These self‐
forming structures are suitable for optical devices such
as low‐loss optical cavities for high‐efficiency LEDs.
The structures are made by annealing GaN NWs with
a thick radial shell, reforming them into hexagonal flat‐
top prisms with six equivalents either m‐ or s‐facets
depending on the initial heights of the top pyramid
and m‐facets of the NWs. This shape is kinetically
controlled and the reformation can be explained with
a phenomenological model based on Wulff
construction that have been developed. It is expected
that the results will inspire further research into
micron‐sized III‐nitride‐based devices.
https://doi.org/10.1002/advs.202001272https://doi.org/10.1002/smll.201907364
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Fabrication and applications of wafer-scale
nanoporous GaN near-infrared distributed Bragg
reflectors School of Microelectronics, Shandong University, Jinan,
250100, PR China
School of Physics, Shandong University, Jinan, 250100, PR
China
Optical Materials
https://doi.org/10.1016/j.optmat.2020.110093
The wafer-scale, near-infrared, and nanoporous (NP)-
GaN distributed Bragg reflectors (DBRs) were
fabricated by using an electrochemical anodization
method for the first time. The peak reflectivity of the
DBR mirrors on the sapphire substrates is ~95% in the
range of 550 nm–1750 nm with different stop-band
widths. To explore its potential applications, a lead-
free all-inorganic perovskite film with a PL emission in
the near-infrared region was grown on a DBR mirror.
Compared to the reference perovskite film, the
photoluminescence intensity of the perovskite film on
the DBR substrate presents more than 4-fold
enhancement, which is in agreement with the
calculated value. The performance enhancement
should be contributable to light-coupling
enhancement of emission light. The near-infrared NP-
GaN DBRs pave the way for developing a range of
perovskite devices for broadband and large-area
applications.
Ultrawide bandgap AlN metasurfaces for ultraviolet
focusing and routing State Key Laboratory of High Performance Complex
Manufacturing, College of Mechanical and Electrical
Engineering, Central South University, Changsha, Hunan
410083, China
State Key Laboratory of Advanced Design and
Manufacturing for Vehicle Body, College of Mechanical and
Vehicle Engineering, Hunan University, Changsha 410082,
China
Research and Development Center for Solid State Lighting,
Institute of Semiconductors, Chinese Academy of Sciences,
Beijing 100083, China
Optics Letters
https://doi.org/10.1364/OL.395909
All-dielectric metasurfaces offer a promising way to
control amplitude, polarization, and phase of light.
However, ultraviolet (UV) component metasurfaces
are rarely reported due to significant absorption loss
for most dielectric materials and the required smaller
footprint or feature size. Here, we demonstrate
broadband UV focusing and routing in both
transmission and reflection modes in simulations by
adopting aluminum nitride (AlN) with ultrawide
bandgap and a waveplate metasurface structure. As
for experiments, the on-axis, off-axis focusing
characteristics in transmission mode have been
investigated at representative UVA (375 nm)
wavelength for the first time, to the best of our
knowledge. Furthermore, we fabricated a UV
transmission router for monowavelength, guiding UV
light to the designated different spatial positions of
the same or different focal planes. Our work is
meaningful for the development of UV photonics
components and devices and would facilitate the
integration and miniaturization of UV nanophotonics.
Revealing the importance of light extraction
efficiency in InGaN/GaN microLEDs via chemical
treatment and dielectric passivation editors-pick Department of Chemical Engineering, University of
California, Santa Barbara, California 93106, USA
Materials Department, University of California, Santa
Barbara, California 93106, USA
Department of Electrical and Computer Engineering,
University of California, Santa Barbara, California 93106,
USA
Applied Physics Letters
https://doi.org/10.1063/5.0011651
Chemical etching and Al2O3 dielectric passivation
were used to minimize nonradiative sidewall defects
in InGaN/GaN microLEDs (mesa diameter = 2–
100 μm), resulting in an increase in external quantum
efficiency (EQE) as the LED size was decreased. Peak
EQEs increased from 8%–10% to 12%–13.5% for mesa
diameters from 100 μm to 2 μm, respectively, and no
measurable leakage currents were seen in current
density–voltage (J–V) characteristics. The position and
shape of EQE curves for all devices were essentially
identical, indicating size-independent ABC model
(Shockley–Read–Hall, radiative, and Auger
recombination) coefficients-behavior that is not
typical of microLEDs as the size decreases. These
trends can be explained by enhancement in light
https://doi.org/10.1016/j.optmat.2020.110093https://doi.org/10.1364/OL.395909https://doi.org/10.1063/5.0011651
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extraction efficiency (LEE), which is only observable
when sidewall defects are minimized, for the smallest
LED sizes. Detailed ray-tracing simulations
substantiate the LEE enhancements.
Enhancing carrier transport and carrier capture with
a good current spreading characteristic via graphene
transparent conductive electrodes in InGaN/GaN
multiple-quantum-well light emitting diodes Department of Applied Physics, National University of
Kaohsiung No. 700, Kaohsiung University Road, Nan-Tzu
Dist., 811, Kaohsiung City, Taiwan (R.O.C.)
LiveStrong Optoelectronics Cooperation, No. 82, Luke 5th
Rd., Kaohsiung City, 821, Taiwan (R.O.C.)
Department of Mechanical Engineering and Advanced
Institute of Manufacturing with High-tech Innovations,
National Chung Cheng University, No. 168, Sec. 1, University
Rd., Chia-yi, 621301, Taiwan (R.O.C.)
Scientific Reports
https://doi.org/10.1038/s41598-020-67274-1
In this work, InGaN/GaN multiple-quantum-wells
light-emitting diodes with and without graphene
transparent conductive electrodes are studied with
current-voltage, electroluminescence, and time-
resolved electroluminescence (TREL) measurements.
The results demonstrate that the applications of
graphene electrodes on LED devices will spread
injection carriers more uniformly into the active region
and therefore result in a larger current density,
broader luminescence area, and stronger EL intensity.
In addition, the TREL data will be further analyzed by
employing a 2-N theoretical model of carrier
transport, capture, and escape processes. The
combined experimental and theoretical results clearly
indicate that those LEDs with graphene transparent
conductive electrodes at p-junctions will have a
shorter hole transport time along the lateral direction
and thus a more efficient current spreading and a
larger luminescence area. In addition, a shorter hole
transport time will also expedite hole capture
processes and result in a shorter capture time and
better light emitting efficiency. Furthermore, as more
carrier injected into the active regions of LEDs, thanks
to graphene transparent conductive electrodes,
excessive carriers need more time to proceed carrier
recombination processes in QWs and result in a longer
carrier recombination time. In short, the LED samples,
with the help of graphene electrodes, are shown to
have a better carrier transport efficiency, better
carrier capture efficiency, and more electron-hole
recombination. These research results provide
important information for the carrier transport,
carrier capture, and recombination processes in
InGaN/GaN MQW LEDs with graphene transparent
conductive electrodes.
Flexible perylenediimide/GaN organic–inorganic
hybrid system with exciting optical and interfacial
properties Photovoltaic Metrology Group, CSIR-National Physical
Laboratory, Dr. K. S. Krishnan Marg, New Delhi, 110012,
India
2D Physics and QHR Metrology Group, CSIR-National
Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi,
110012, India
Photonics Materials Metrology Group, CSIR-National
Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi,
110012, India
Thin Film Gas Metrology Group, CSIR-National Physical
Laboratory, Dr. K. S. Krishnan Marg, New Delhi, 110012,
India
Department of Electronics and Communication
Engineering, Indian Institute of Information Technology
Allahabad, Prayagraj, 211015, India
Spintronics and Magnetic Materials Laboratory,
Department of Applied Sciences, Indian Institute of
Information Technology Allahabad, Prayagraj, 211015, India
Scientific Reports
https://doi.org/10.1038/s41598-020-67531-3
We report the band gap tuning and facilitated charge
transport at perylenediimide (PDI)/GaN interface in
organic–inorganic hybrid nanostructure system over
flexible titanium (Ti) foil. Energy levels of the materials
perfectly align and facilitate high efficiency charge
transfer from electron rich n-GaN to electron deficient
PDI molecules. Proper interface formation resulted in
band gap tuning as well as facilitated electron
transport as evident in I–V characteristics. Growth of
PDI/GaN hybrid system with band gap tuning from
ultra-violet to visible region and excellent electrical
properties open up new paradigm for fabrication of
efficient optoelectronics devices on flexible
substrates.
https://doi.org/10.1038/s41598-020-67274-1https://doi.org/10.1038/s41598-020-67531-3
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GaN/AlN Multiple Quantum Wells grown by
Molecular Beam Epitaxy: Effect of growth kinetics on
radiative recombination efficiency Centre for Research in Nanoscience and Nanotechnology,
University of Calcutta, JD2 Sector III Salt Lake City, Kolkata-
700106, West Bengal, India
Institute of Radio Physics and Electronics, University of
Calcutta, 92 A. P. C. Road, Kolkata-700009, West Bengal,
India
School of Biological Sciences, Indian Association for the
Cultivation of Science, Kolkata 700032, India
Thin Solid Films
https://doi.org/10.1016/j.tsf.2020.138216
Ultraviolet (UV) optoelectronic devices based on
binary GaN quantum wells have been widely reported
in the literature. The internal quantum efficiency (IQE)
of such structures is relatively low due to the large
dislocation densities generated during heteroepitaxial
deposition on to non lattice-matched substrates.
Enhancement of IQE is possible through the use of
expensive lattice-matched substrates or by using
complex dislocation density reducing mechanisms. In
this paper we have investigated growth mechanisms
of GaN/AlN multiple quantum wells (MQWs) using
Plasma Assisted Molecular Beam Epitaxy. Specifically
the modulation of the surface diffusivity of adatoms
has been carried out through choice of appropriate
growth parameters, such as the group-III to group-V
flux ratio. Our results indicate that this leads to
modification of not only the surface morphology, but
also the abruptness of the well-barrier interface.
Under conditions of growth where surface
morphology was atomically flat, the interfaces are
relatively diffuse. The IQE for such structures, as
measured by the ratio of room temperature
photoluminescence intensity to that measured at 4 K,
is rather low typically ∼10%. Use of near
stoichiometric growth conditions however lead to a
reduction of the surface diffusivity of adatoms, and
the formation of spontaneous nanostructures in the
form of nano-dots of about 20 nm in diameter and
high levels of uniformity. The IQE for GaN/AlN MQWs
grown under such conditions is increased to as high as
28% even for samples with large dislocation densities.
Thus, growth under such conditions can mitigate the
detrimental effects of non-radiative recombination
centers associated with dislocations by spatial
localization of electron-hole pairs. These results are
important to many applications, including UV light
emitting diodes.
Enhancement of the optoelectronic characteristics of
deep ultraviolet nanowire laser diodes by induction
of bulk polarization charge with graded AlN
composition in AlxGa1-xN waveguide National Center for International Joint Research of
Electronic Materials and Systems, Zhengzhou University,
Zhengzhou, Henan, China
International Joint-Laboratory of Electronic Materials and
Systems of Henan Province, Zhengzhou University,
Zhengzhou, Henan, China
Department of Electronics and Information Engineering,
School of Information Engineering, Zhengzhou University,
Zhengzhou, Henan, China
Zhengzhou Way Electronic Co. Ltd, Zhengzhou, Henan,
China
Superlattices and Microstructures
https://doi.org/10.1016/j.spmi.2020.106643
AlGaN based Nanowire laser diodes (NW-LDs) grown
on sapphire substrates have strong polarization
induced electric field. Such electric field has the ability
to degrade the optoelectronic characteristics of deep
ultraviolet (DUV) NW-LD. In this work, a graded AlN
composition AlxGa1-xN waveguide (WG) layer is used
for the enhancement of DUV NW-LD performance.
Grading of WG induces bulk polarization charges
which compensates the effect of polarization induced
electric field. According to the calculated
optoelectronic characteristics of NW-LD, it is found
that grading of n-type WG (n-WG) increases the
optical confinement factor (OCF) by 82%. Fortunately,
the proposed graded n-WG structure suppresses the
leakage of optical field from active region and
enhances carrier injection efficiency. Furthermore, if
both n-WG and p-WG graded layers are used, the
improvement is not obvious because of the current
leakage from graded p-WG. Thus, graded n-WG based
NW-LD gives highest 33.5% OCF with the lowest mA
and 4.59 V threshold current and voltage respectively.
https://doi.org/10.1016/j.tsf.2020.138216https://doi.org/10.1016/j.spmi.2020.106643
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High nitrogen flux plasma-assisted molecular bean
epitaxy growth of InxGa1-xN films Materials Department, University of California, Santa
Barbara, CA 93106, United States
Journal of Crystal Growth
https://doi.org/10.1016/j.jcrysgro.2020.125738
Growth of efficient III-N based light emitting devices
by plasma assisted molecular beam epitaxy has been
elusive, even though the technique has attractive
advantages in comparison to metal organic chemical
vapor deposition. Modern high-flux radio frequency
plasma systems could remedy this issue by enabling
growth of InxGa1-xN at higher temperatures than
previously possible, likely improving the material
quality. In this work, active nitrogen fluxes of up to 3.5
μm/h GaN-equivalent growth rate were employed to
grow InxGa1-xN alloys. InxGa1-xN growth rates of 1.3
μm/h were demonstrated at growth temperatures of
550 °C and 600 °C with maximum film compositions of
In0.25Ga0.75N and In0.21Ga0.79N, respectively. A
composition of In0.05Ga0.95N was observed in a film
grown at 700 °C with smooth step-terrace
morphology.
The influence of point defects on AlGaN-based deep
ultraviolet LEDs State Key Laboratory of Integrated Optoelectronics,
Institute of Semiconductors, Chinese Academy of Sciences,
No. A35, Qinghua East Road, Haidian District, Beijing,
100083, China
Center of Materials Science and Optoelectronic
Engineering, University of Chinese Academy of Sciences, No.
19A, Yuquan Road, Shijingshan District, Beijing, 100049,
China
School of Physics and Astronomy, University of Nottingham,
Nottingham NG7 2RD, UK
Shanghai Key Laboratory of Multidimensional Information
Processing, School of Communication and Electronic
Engineering, East China Normal University, Shanghai, China
Physics Department, Faculty of Science, Princess Nourah
Bint Abdulrahman University, Riyadh, Saudi Arabia
Journal of Alloys and Compounds
https://doi.org/10.1016/j.jallcom.2020.156177
AlGaN-based deep ultraviolet LEDs with high Al
composition are promising for many applications,
including air- or water-purification, fluorescence
sensing, etc. However, to realize their full potential, it
is important to understand the impact of the point
defects on the device performance. Here, we
investigate the defects in the 26 nm AlGaN-based
deep ultraviolet LEDs after degradation systematically
with a combination of different analytical
technologies. The results show that point defects
increase after the degradation. The generated defects
during the stress lead to a carrier redistribution in the
active region and the induced point defects during the
degradation are located within the multi-quantum
wells (MQWs) region, especially in the first quantum
well near the p side of the LED chip. The dislocation
lines in the MQWs region were also observed after the
degradation, which can lead to the Mg diffusion along
the dislocation line. These findings are important to
understand the defects in AlGaN quantum wells and
further improve AlGaN-based deep ultraviolet LEDs
performance.
Improved contact properties of single-walled carbon
nanotube on p-AlGaN layers after microwave post-
treatment Department of Electrical Engineering, Sejong University,
Seoul, 05006, South Korea
Department of Electrical Engineering and Computer
Science, University of Michigan, Ann Arbor, MI, 48109,
United States
Materials Chemistry and Physics
https://doi.org/10.1016/j.matchemphys.2020.123471
We present improved contact and transparent
properties of single-walled carbon nanotube (SWNT)
transparent conductive electrodes (TCEs) on the p-
AlGaN layer via a post microwave treatment (MWT)
method. As a result, the contact resistance of the
MWT-SWNT TCEs was observed to be 9.7 × 10-2
Ω∙cm2, which was 26.5% lower than that of pristine
sample, while the transmittance is improved by 1.6%
(at the wavelengths of 365 nm) after the MWT. In
addition, the results of material and chemical analyses
show that these improvements might contribute to
the reduction in the Schottky barrier height between
the TCE and the p-AlGaN layer, through both a
generation of Ga vacancies in p-AlGaN interface and a
decrease of oxygen vacancies that can increase hole
concentration in SWNTs.
https://doi.org/10.1016/j.jcrysgro.2020.125738https://doi.org/10.1016/j.jallcom.2020.156177https://doi.org/10.1016/j.matchemphys.2020.123471
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GANEXT | GaN Technology for Optoelectronics & Electronics Newsletter No. 06 | 17
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Structural, optical and photoresponse characteristics
of metal-insulator-semiconductor (MIS) type
Au/Ni/CeO2/GaN Schottky barrier ultraviolet
photodetector Department of Physics, Madanapalle Institute of
Technology and Science, Madanapalle, 517 325, Andhra
Pradesh, India
CONACYT–Universidad Juárez Autónoma de Tabasco,
Centro de Investigación de Ciencia y Tecnología Aplicada de
Tabasco (CICTAT), Cunduacán, C.P 86690, Mexico
Department of Physics, Rajeev Gandhi Memorial College of
Engineering and Technology, Nandyal, 518 501, Andhra
Pradesh, India
Instituto de Ciencias Físicas, Universidad Nacional
Autónoma de México, C.P 62210 Cuernavaca, Morelos,
México
Department of Physics, Presidency University, Bangalore,
560064, Karnataka, India
IISER Berhampur, Berhampur, 760 010, Odisha, India
Department of Electronic Science, Kurukshetra University,
Kurukshetra, 136119, India
School of Mechanical Engineering, Yeungnam University,
Gyeongsan, 38541, Republic of Korea
Materials Science in Semiconductor Processing
https://doi.org/10.1016/j.mssp.2020.105190
GaN based metal-insulator-semiconductor (MIS) type
ultraviolet photodetector was fabricated and
investigated using high-k dielectric CeO2 as an
insulating oxide layer. Using XRD analysis, the phase
formation of the as-deposited CeO2 films on GaN was
found to be cubic fluorite. Non-contact mode atomic
force microscopy technique was utilized and explored
the surface morphology of CeO2 films on GaN
composed of prearranged clusters of spherical shape
with an average rms surface roughness of 0.428 μm.
XPS analysis has revealed the existence of two
oxidation states such as Ce3+ and Ce4+ in the Ce3d
spectral envelop. Using absorbance versus wavelength
data, the Tauc's plot was plotted and calculated a
direct optical bandgap of 3.52 eV. The current-voltage
(I–V) characteristics extracted from the device
revealed the symmetric behavior or formation of back-
to-back Schottky barrier at the metal-semiconductor
(MS) interface. Photoresponsivity of the device at +10
V bias was calculated as 28.99 A/W and it is higher
compared to the values extracted from metal-
semiconductor-metal (MSM) type UV PDs reported in
the literature. Furthermore, the transient response
characteristics of the prepared device showed good
stability with almost same rise time and fall time of
~2.73 s and ~5.35 s, respectively. Based on the device
performance, the proposed MIS type structure could
be a suitable for the development of ultraviolet
photodetectors.
Phosphor-free, color-mixed, and efficient illuminant:
Multi-chip packaged LEDs for optimizing blue light
hazard and non-visual biological effects National Institute of LED on Silicon Substrate, Nanchang
University, Nanchang, Jiangxi 330096, China
Optics and Lasers in Engineering
https://doi.org/10.1016/j.optlaseng.2020.106174
Currently many evaluation models on the
photobiological effects (PBE) of light sources do not
consider the influence of age and luminance on the
pupil diameter, which affects the light radiation
intensity on the human retina. In this study, the pupil
diameter is taken into consideration when evaluating
the PBE of several light sources. Moreover, the
correction factor M is proposed. The blue light hazard
(BLH) efficacy and the circadian rhythm (CR) effects of
the daylight at dusk, together with three indoor light
sources with a correlated color temperature (CCT) of
about 3000 K were evaluated by using a corrected
evaluation model. The results show that an
incandescent lamp is more photobiologically friendly
for humans, despite being inefficient. Based on high
wall-plug efficiency (WPE) GaN-based yellow (565 nm,
24.3%@20 A/cm2) and green (522 nm, 41.3%@20
A/cm2) LEDs on silicon substrate, incandescent-like
spectrum and phosphor-free color-mixed white LEDs
(CM-LEDs) with a general color rendering index (CRI)
of 94, a CCT of 2866 K, and an efficiency of 131 lm/W
were manufactured by mixing blue, cyan, green,
yellow and red LEDs. The PBE evaluation results of
such CM-LEDs are superior to those of an incandescent
lamp. Moreover, blue light free and candlelight-toned
LEDs with an efficiency of 120.3 lm/W, a general CRI of
84, a special CRI R9 of 93.3, and a CCT of 1810 K were
fabricated by mixing yellow and red LEDs (R&Y-mixed
LEDs). The R&Y-mixed LEDs show no blue light
weighted quantities and have a weaker influence on
the CR shift. They are photobiologically friendly for
https://doi.org/10.1016/j.mssp.2020.105190https://doi.org/10.1016/j.optlaseng.2020.106174
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GANEXT | GaN Technology for Optoelectronics & Electronics Newsletter No. 06 | 18
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humans and suitable for nocturnal indoor and outdoor
lighting environments.
Light Extraction Efficiency Optimization of AlGaN-
Based Deep-Ultraviolet Light-Emitting Diodes The Institute of Technological Sciences, Wuhan University,
Wuhan 430072, People's Republic of China
Center for Photonics and Semiconductors, School of Power
and Mechanical Engineering, Wuhan University, Wuhan
430072, People's Republic of China
State Key Laboratory of Applied Optics, Changchun Institute
of Optics, Fine Mechanics and Physics, Chinese Academy of
Sciences, Changchun 130033, People's Republic of China
ECS Journal of Solid State Science and Technology
https://doi.org/10.1149/2162-8777/ab85c0
Using finite-difference time-domain method, the light
extraction efficiency (LEE) of AlGaN-based deep-
ultraviolet light-emitting diodes (DUV LEDs) is
investigated. Simulation results show that compared
to flat sapphire substrate, the nano-patterned
sapphire substrate (NPSS) expands the extraction
angles of top surface and sidewalls. As a result, the LEE
of transverse-magnetic (TM) polarized light is
improved significantly. Roughening on the backside of
n-AlGaN surface significantly enhances the LEE of top
surface of thin-film flip-chip DUV LEDs. However, the
LEE of sidewalls of thin-film flip-chip DUV LEDs is
greatly weakened. For bare DUV LED, the LEE of flip-
chip LED on NPSS is estimated to be about 15%, which
is around 50% higher than that of thin-film flip-chip
DUV LED with roughening on the backside of n-AlGaN
surface.
Development of polarity inversion in a GaN
waveguide structure for modal phase matching Institute of Photonics and Nanotechnology, Vilnius
University, Saulėtekio ave. 3, 10257, Vilnius, Lithuania
State research institute Center for Physical Sciences and
Technology, Savanorių ave. 231, 02300, Vilnius, Lithuania
Picosun Oy, Tietotie 3, 02150, Espoo, Finland
Journal of Materials Science
https://doi.org/10.1007/s10853-020-04831-z
In this work, we report on the fabrication of a
GaN/AlGaN waveguiding structure dedicated to modal
phase matching, where GaN waveguide has planar
polarity inversion. First, we optimized the growth
conditions for the AlGaN epilayer. Second, on top of
the AlGaN epilayer, we fabricated the waveguiding
structure starting with the growth of the Ga-polar GaN
epilayer followed by atomic layer deposition (ALD) of
an Al2O3 layer, then, continuing with the growth of N-
polar GaN epilayer. We tested several layer
thicknesses, but with 20 nm we managed to inverse
the GaN polarity from Ga to N. To confirm the N-
polarity, we etched the GaN epilayer surface in
aqueous KOH solution. We performed out-of-plane
(0002) and in-plane (11–20) X-ray diffraction and
rocking curve measurements to estimate the
crystalline quality of the AlGaN epilayer, Ga- and N-
polar GaN epilayer. Atomic force microscopy
measurement lets us evaluate the epilayer surface
morphology and roughness. Optical and scanning
electron microscopy inspection revealed
characteristic hexagonal N-polar GaN epilayer surface.
We used high-resolution transmission electron
microscopy to investigate the crystallinity and
orientation of the Ga- and N-polar GaN epilayer, also
the Al2O3 ALD layer, the interface quality of the
waveguide structure.
Ultrahigh Gain of a Vacuum-Ultraviolet
Photodetector Based on a Heterojunction Structure
of AlN Nanowires and NiO Quantum Dots School of Physics, Harbin Institute of Technology, Harbin
150001, China
Interdisciplinary Science Research Center, Harbin Institute
of Technology, Harbin 150001, China
Key Laboratory of Nanodevices and Applications, Suzhou
Institute of Nano-tech and Nano-bionics, Chinese Academy
of Science, Suzhou 215123, China
School of Materials Science & Engineering, Harbin Institute
of Technology, Harbin 150001, China
National Key Laboratory of Science and Technology on
Advanced Composites in Special Environments, Harbin
Institute of Technology, Harbin 150001, China
PHYSICAL REVIEW APPLIED
https://doi.org/10.1103/PhysRevApplied.13.064036
Aluminum nitride (AlN) is a promising candidate for
the manufacture of vacuum ultraviolet (VUV)
photodetectors. However, its poor electrical
conductivity limits its applications. Herein, a high-
performance AlN nanowire (NW)-NiO quantum dot
(QD) based VUV photodetector is constructed via a
https://doi.org/10.1149/2162-8777/ab85c0https://doi.org/10.1007/s10853-020-04831-zhttps://doi.org/10.1103/PhysRevApplied.13.064036
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GANEXT | GaN Technology for Optoelectronics & Electronics Newsletter No. 06 | 19
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mixed-dimensional strategy. The formation of isolated
nanoscale p-n heterojunctions greatly increases the
concentration of photogenerated electrons, resulting
in an ultrahigh photoconductive gain (9.96) in the AlN
NW-NiO QD material, which is about 27-fold higher
than that of AlN NW (0.368). In addition, the
significant improvement in both photocurrent and
response speed convincingly suggest the great
potential of AlN NW-NiO QD based VUV
photodetectors. Furthermore, the properties of these
photodetectors in an irradiation environment are also
evaluated here. It is found that AlN NW exhibits
excellent anti-irradiation characteristics towards both
electron and proton irradiation, while the AlN NW-NiO
QD material also presents promising potential under
low-dose electron irradiation. This study can be used
as a guideline to design and fabricate high-
performance VUV photodetectors based on wide-
band-gap semiconductors coupled with other
nanostructured systems.
Tunable nanostructured distributed Bragg reflectors
for III-nitride optoelectronic applications Institute of Marine Science and Technology, Shandong
University, Qingdao 266237, China
Department of Microelectronics, Shandong University,
Ji'nan 250100, China
Depth Perception Institute, Jiangsu Industrial Technology
Research Institute, jiangsu, China
Huaian Aucksun Optoelectronics Technology Ltd., Huai'an,
China
RSC Advances
https://doi.org/10.1039/D0RA03569F
Highly reflective and conductive distributed Bragg
reflectors (DBRs) are the key for high-performance III-
nitride optoelectronic devices, such as vertical cavity
surface emitting lasers (VCSELs), but they still suffer
from lack of lattice-matched conductive DBR and
uncontrollable processes. In this work, nanostructured
GaN-based DBRs were fabricated and optimized both
experimentally and simulatively using electrochemical
etching (EC) in different electrolytes using the
transfer-matrix method (TMM) to obtain uniform
wafer scale, highly reflective and conductive reflectors
for the application of GaN-based optoelectronics. The
results revealed that a nanostructured GaN-based
DBR with high reflectivity (>93%) and broad stopband
(∼80 nm) could be achieved in neutral sodium nitrate
by EC, and the nanostructured GaN DBR with a full
visible spectrum range could be designed by tuning
the thickness of the nanostructured GaN DBR layers.
The photoluminescence (PL) and light-out power
enhancements of the GaN-based micro-LED by
incorporating the fabricated nanostructured GaN-
based DBR were 6 times and 150% without the
degradation of electrical performance, respectively,
which contributed to strong light scattering from the
DBR layers. We believe that this work will pave a way
to obtain high-performance GaN-based
optoelectronic devices and guide the applications in
the field of flexible devices and biomedical sensors.
A bow-free freestanding GaN wafer Department of Electronics and Computer Engineering,
Hanyang University, Seoul, Republic of Korea
RSC Advances
https://doi.org/10.1039/D0RA01024C
For applications as high-brightness light-emitting-
diodes, a bow-free freestanding gallium nitride (GaN)
wafer 2 inch in diameter and ∼185 μm in thickness
was fabricated by process-designing pit and mirror
GaN layers grown via hydride-vapor-phase epitaxy,
laser lift-off, N-face polishing of the pit GaN layer, and
three-step polishing of the mirror GaN layer using 3.0
μm-, 0.5 μm-, and 50 nm-diameter diamond abrasives
and by inductively-coupled-plasma reactive-ion
etching. The considerably large concave shape of the
GaN wafer could be decreased by controlling the
removal amount of the Ga-face mirror layer during the
first step of the polishing process, which approached a
bow-free shape or changed with further polishing; this
well correlated with the residual stress of the polished
GaN wafer.
https://doi.org/10.1039/D0RA03569Fhttps://doi.org/10.1039/D0RA01024C
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GANEXT | GaN Technology for Optoelectronics & Electronics Newsletter No. 06 | 20
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ELECTRONICS Group leader: Farid Medjoub (CNRS-IEMN)
Information selected by Farid Medjoub (CNRS-IEMN), Jean-Claude Dejaeger (CNRS-IEMN) and Yvon Cordier (CNRS-CRHEA)
On-Wafer Fast Evaluation of Failure Mechanism of
0.25-μm AlGaN/GaN HEMTs: Evidence of Sidewall
Indiffusion Department of Information Engineering, University of
Padua, 35131 Padua, Italy
United Monolithic Semiconductor, 89081 Ulm, Germany
Fraunhofer Institute for Microstructure of Materials and
Systems (IMWS), 06120 Halle, Germany
IEEE Transactions on Electron Devices
https://doi.org/10.1109/TED.2020.2996983
In this article, we present the results of on-wafer
short-term (24 h) stress tests carried out on 0.25-μm
AlGaN/GaN HEMTs. Devices on-wafer were submitted
to 24-h dc tests, at various gate and drain voltage
values corresponding to dissipated power densities PD
up to 40 W/mm, with estimated channel temperature
≅ 375 °C. GEN1 devices adopted a Ni/Pt/Au gate
metallization and conventional plasma-enhanced
chemical vapor deposition (PE-CVD) SiN passivation; in
GEN2 devices, a modified gate metallization and a
two-layer SiN passivation were adopted. When tested
at Pd >25 W/mm, a substantial decrease of drain
current ID and transconductance gₘ was measured in
GEN1 HEMTs, without any significant shift of threshold
voltage. Failure analysis revealed that Au and O
interdiffusion took place from the sidewalls; Au
gradually substituted Ni as a Schottky contact, while O,
in the presence of high electric field, high
temperature, and high current, promoted (Al)GaN
oxidation and pitting. On the contrary, negligible
degradation was found after high temperature
storage of GEN1 devices without applied bias, up to
450 °C. In GEN2, process modification was effective in
reducing the impact of this failure mechanism,
resulting in only 5% gₘ decrease after 24 h at a
junction temperature of 375 °C with PD = 38 W/mm.
Results demonstrate the effectiveness of the adopted
on-wafer screening methodology in identifying
potentially dangerous failure mechanisms.
Analysis and optimization of GaN based Multi-
channels FinFETs Graduate Institute of Photonics and Optoelectronics,
National Taiwan University, 33561 Taipei, Taipei Taiwan
10617
IEEE Transactions on Nanotechnology
https://doi.org/10.1109/TNANO.2020.2998840
In this work, the design of multi-channels tri-gate
AlGaN/GaN high-electron-mobility transistors
(HEMTs) is optimized for high-power and high-
frequency applications. The application of FinFET
structure has reduced the short channel effect as the
gate length of the device shrinks. But sidewall
depletion of two dimensional electron gas reduces the
current density is another issue to be overcome. Using
multiple AlGaN/GaN channels has been proposed to
compensate the current loss from reduction of
channel width. With a full self-consistent 3D modelling
on carrier transport and heating issues, the design
issue and optimized for multi-channel FinFETs has
been investigated. With a proper design, the
optimized normally-on four channel transistor show a
3.2 times higher maximum transconductance, as
compared to the single channel tri-gate device. And
the performance of unit current gain frequency also
has an improvement in mu