6000107 ieee journal of selected topics in quantum ... · the residual pr layer and dielectric...

6000107 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 21, NO. 4, JULY/AUGUST 2015

Enhanced Light Extraction Efficiency of GaN-BasedHybrid Nanorods Light-Emitting Diodes

Jhih-Kai Huang, Che-Yu Liu, Tzi-Pei Chen, Hung-Wen Huang, Fang-I Lai, Po-Tsung Lee, Member, IEEE,Chung-Hsiang Lin, Chun-Yen Chang, Tsung Sheng Kao, and Hao-Chung Kuo, Senior Member, IEEE

Abstract—High light extraction GaN-based light-emittingdiodes (LEDs) with a hybrid structure of straight nanorods lo-cated in an array of microholes have been successfully demon-strated. Via the nanoimprint lithography and photolithographytechniques, high aspect-ratio light-guiding InGaN/GaN nanorodscan be fabricated and regularly arranged in microholes, result-ing in a great improvement of the light extraction for the GaN-based LED device. The light output power of the hybrid nanorodsLED is 22.04 mW at the driving current standard of 25.4 A/cm2,an enhancement of 38.7% to the conventional GaN-based LEDs.Furthermore, with a modification of the hybrid structures’ dimen-sions and locations, the emitted optical energy can be redistributedto obtain light-emitting devices with homogenueous optical fielddistributions.

Index Terms—Light emitting diodes, optoelectronic devices,nanotechnology, lithography.

I. INTRODUCTION

GALLIUM-nitride (GaN) based light-emitting diodes(LEDs) have attracted intensive interest among scientists

and technologists over past twenty years for their promisingapplications such as monitor backlight, outdoor full-color dis-play, and solid-state lighting [1]–[4]. However, the total lightoutput from the GaN-based LEDs is still rather low which maylimit their applications in practice. Several key advances havebeen reported in the fields of III-Nitride LEDs [5], [6], includ-ing non-/semi-polar InGaN QWs [7], large overlap InGaN QWs[8], [9], ITO spreading layer [10] and InGaN/GaN LED’s re-liability [11]. Typically, due to the different refractive indicesbetween the GaN materials and the ambient air, only about 4%of the light emitted from the active regions can escape from theLED surface, while the reflected light from the bottom sapphirewafers is absorbed by the constituent materials after the multi-ple internal reflections [12]. Such an output quantity is unable

Manuscript received September 27, 2014; revised December 30, 2014; ac-cepted January 3, 2015. Date of publication January 9, 2015; date of currentversion February 27, 2015. This work was supported in part by the Ministry ofScience and Technology, China.

J.-K. Huang, C.-Y. Liu, T.-P. Chen, H.-W. Huang, P. T. Lee, T. S. Kao,and H.-C. Kuo are with the Department of Photonics and Institute ofElectro-Optical Engineering, National Chiao Tung University, Hsinchu 300,Taiwan (e-mail: [email protected]; [email protected];[email protected]; [email protected]; [email protected]; [email protected]; [email protected]).

F.-I. Lai and C. Y. Chang are with the Department of Electrical Engineering,Yuan Ze University, Chung-Li 320, Taiwan (e-mail: [email protected];[email protected]).

C.-H. Lin is with the Luxtaltek Corporation, Miaoli 350, Taiwan (e-mail:[email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JSTQE.2015.2389529

to meet the increasing demands in today’s industries. Thus, howto further promote the light emission efficiency and the outputoptical power of GaN-based LEDs have become one of the mostimportant topics in the research field [13]–[30].

To obtain high output power LED devices, first of all, is toenhance the light extraction efficiency (LEE), which can bepromoted by eliminating the light reflections in LED struc-ture and increasing the number of photons escaped from theactive regions. Regarding the elimination of light reflections,several advanced methods have been proposed and investigatedsuch as the textured structures on the p-GaN surface [13], [14],double-embedded photonic crystals [15], [16], self-assembledmicrolens arrays [17], [18], concave microstructures via im-printing method [19], [20], embedded air-voids photonic crys-tals in GaN layers [21], [22], and patterned micro-holes arrayson LEDs surface [23], [24]. These methods have been success-fully demonstrated that the LEE could be promoted. Moreover,in terms of increasing the number of emitted photons, severalgroups have made their great efforts to produce GaN nanorodsin the GaN-based LEDs structure [25]–[30]. These nanorodsnot only provide a large sidewall-surface area as the pathwaysfor the photons escape, but also function as light guiding pil-lars to extract the photons in the longitudinal direction. In thispaper, we intend to take the both advantages by exploiting adesigned hybrid structure of InGaN/GaN multi quantum wells(MQWs) nanorods within an array of microholes, simultane-ously reducing the light reflections and increasing the escapedphotons to enhance the light extraction in the new type LEDdevice. Meanwhile, via the nano-imprint [31] and photolithog-raphy technologies, well-arranged InGaN/GaN nanorods can begenerated in microholes as proposed, giving the opportunitiesin reliable mass production in future lighting industry.

II. EXPERIMENT

To illustrate the fabrication process of InGaN/GaN nanorodsin microholes, a schematic diagram to describe the layer struc-ture of a GaN-based LED wafer and how the nanorods gen-erated in microholes is represented in Fig. 1. The LED waferwas prepared via the metal organic chemical vapor deposition(MOCVD) method and from the bottom to the top, sequen-tially consisted a 50 nm GaN nucleation layer, a 2 μm un-doped GaN buffer layer, a 3 μm Si-doped n-GaN layer, 10 pairsIn0.21Ga0.79N/GaN MQWs with a central wavelength of 460 nmand a 0.2 μm Mg-doped p-GaN layer grow on a patterned sap-phire substrate.

After the growth of the LED wafer, the nano-imprint lithog-raphy (NIL) and photolithography technique were applied to

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HUANG et al.: ENHANCED LIGHT EXTRACTION EFFICIENCY OF GaN-BASED HYBRID NANORODS LIGHT-EMITTING DIODES 6000107

Fig. 1. Schematic diagrams. (a) Layer structure of a hybrid nanorods GaN-based LED with nanorods located in an array of micro-holes. (b)–(e) Brieffabrication flow chart of the nanorods fabrications in microholes arrays.

synthesis the GaN nanorods within microholes arrays. Fig. 1(b)illustrates the flow chart of the nano-rods inside the micro-holesfabrications process. First, a 400 nm-thick SiO2 layer was de-posited on the surface of the prepared LED wafer by a plasma-enhanced chemical vapor deposition and then an imprint-resist(IR) layer of 360 nm was coated onto the prepared SiO2 layerby spin coating at a rotational speed of 3000 rpm. By placingand releasing a nano-imprint mold on the IR layer, a 12-foldphotonic quasi-periodic crystal pattern would be transferred tothe IR layer, forming SiO2 dielectric nano-discs at 400 nm indiameter on the wafer surface. A photo-resist (PR) layer with athickness of 2 μm was coated afterwards on the dielectric layerby a spin coater operated at a rotational speed of 3000 rpm. Astandard photolithography method was utilized to fabricate apattern of micro-holes arrays on the PR layer. Then, the LEDwafer with a micro-patterned PR layer and a nano-patterneddielectric layer was etched by an inductively coupled plasma re-active ion etching (ICP-RIE) system with mixed process gasesof Cl2 and BCl3 (Cl2 /BCl3 = 20/10 sccm) at a bias power of80 W and ICP power of 100 W. After the dry etching process,the residual PR layer and dielectric layer were removed via awet-bench system.

Finally, a hybrid structure of uniformly arranged nanorodslocated in microholes arrays was formed on the entire LEDwafer by using NIL and standard lithography technique.

Fig. 2. The (a) tilt-view and (b) cross-section SEM images of nanorods inmicroholes arrays. The diameter of the micro-holes is around 15 μm, while theheight and the diameter of nanorods are 1.2 and 0.45 μm, respectively.

To complete the LED chip, a 0.24 μm indium tin oxide(ITO) thin film as a contact layer was e-beam evaporated onthe top of the above hybrid nanorods LED wafer, while 1.4 μmp-pad and n-pad electrodes were produced onto the ITO layerand n-GaN layer surface, respectively. Finally, the high lightextraction hybrid nanorods LED have been demonstrated. Bydifferent current densities driving, the intensity of the outputlight emission from the LED chip can be acquired.

A clear tilt-view field emission scanning electron microscope(Hitachi S-4800) image of the fabricated nanorods array withina microhole was shown in the Fig. 2(a). Fig. 2(a) and (b) showthe tilt-view and cross-section SEM images of the hybrid struc-tures of nanorods in microholes, respectively. In Fig. 2(a), theimage shows an array of nanorods in a microhole on a LEDchip, while the diameter of the micro-hole is around 15 μm.As the cross-section SEM image represents in Fig. 2(b), via thefabrication process, high aspect-ratio straight nanorods can befabricated with a precise control of different pitches, dimen-sions, and depths etc. In this case, the chip size of whole LEDdevices is 300 μm × 300 μm, while the height and the diam-eter of the nanorods is around 1.2 μm and 450 nm, respectively.

III. RESULTS AND DISCUSSION

The intensity–current–voltage (L–I–V) performance of thehybrid nanorods LEDs was investigated by conducting the elec-troluminescence (EL) measurements using an integrating spheresystem. Fig. 3 shows the L–I–V characteristics of the nanorods


Fig. 3. The intensity–current–voltage (L–I–V) characteristics of the conven-tional (black circles), microholes (red triangles) and hybrid nanorods (bluesquares) LEDs.

LED chips, accompanied with the comparison of the conven-tional and microholes LEDs. Here, the height of the MQWsnanorods is 1.2 μm. In the I–V characteristics, we found that theforward voltages among the three types LED structures are ap-proximate to each other at the same current density, indicatingthat the fabrication process of the constituent microholes andnanorods does not destroy the electric properties of the LEDcomponents. The similar forward voltage of the three types ofLED chips is also due to the limited total area of the diggingmicroholes. In terms of the L-I curve, at the current densityof 25.4 A/cm2, which is corresponding to a driving current of20 mA for the conventional LED, the hybrid nanorods LED chipexhibits an enhanced optical power of 22.04 mW, while the con-ventional and microholes LEDs give the optical power at 15.89and 21.08 mW, respectively. Compared with the conventionalGaN-based LED device, the hybrid nanorods LEDs exhibit anoutput light enhancement of 38.7%. In the hybrid structures,the constituent microholes provide an increase of the light scat-tering from the LED chips and the exposed MQWs from thesidewall area. Also, the reduction in total active region by theetched microholes is considered to increase the current density,promoting the photons generation at per unit area. Accordingto the work done by Hsueh et. al. and Lai et. al. [23], [24], themicro-holes structure acts as scattering media to improve theLEE. Regarding the high aspect-ratio nanorods, they functionas light-guiding pillars to support more light extraction paths forphotons escaping from the LED devices. In addition, the pat-terned ITO layer was designed to cover the most area of p-GaNsurface except the hybrid region of microholes and nanorods,preventing the current leaking from the sidewall. As a result, ap-plying the hybrid structures of nanorods in a microholes array tothe LED devices, light extraction performance can be enhanced,increasing the output optical energy. The hybrid structures notonly can be employed in current LED devices, but also may beexpandable to the photovoltaic components with flexible wave-length and material choices, giving the opportunities in reliablemass production in future industry.

The wall plug efficiency (WPE) η of the LEDs operated at20 mA can be calculated as follows:

η =Pphoton

Pelec=

Pphoton

I × V(1)

Fig. 4. The microscope images of the (a) microholes and (b) hybrid nanorodsGaN-based LEDs. The injected current is at 5 mA. At a high injected current of20 mA, (c) and (d) represent the 3-D beam view images of the microholes andhybrid nanorods LEDs, respectively.

where Pphoton and Pelec indicate the average light output powerand the input electrical power, respectively. The value of theaverage input electrical power can be acquired from the inputcurrent I and the operation voltage V. According to this equation,the WPE of the hybrid nanorods LED device is estimated around29%, while the conventional and microholes LEDs give thevalue at 24.8% and 27.7%, respectively. Thus, even though thelight emitting area is decreased due to the reduced active region,we still can acquire a better energy conversion efficiency onthe hybfied nanorods LEDs by a compensation of the increasedcurrent density and the enhanced LEE.

Fig. 4(a) and (b) respectively show the optical microscopeimages of a microholes LED and a hybrid nanorods LED at thedriving current of 5 mA. In this low current setting, the lightextraction performance between these two structured LEDs canbe compared and analyzed. Here, a neutral density filter of lightintensity was applied in the microscope system operated at adark condition. In Fig. 4(a), light from the constituent micro-holes is much weaker than that from the surrounding MQWsregions, indicating that photon extraction from the microholesLED device is limited at low current injection. In terms of theLED device with the hybrid structure of nanorods in microholes,at the same injected current, luminescence excited from the mi-croholes region is enhanced with the existence of nanorods.Since the current spreading cannot form a complete path atthe locations of nanorods, photons from the microholes in thehybrid nanorods LEDs are not generated from the MQWs inthe InGaN/GaN nanorods. Light from the bright micorholesin the hybrid nanorods LEDs result from the superior light ex-traction between the nanords. The high aspect-ratio InGaN/GaNnanorods function as light guiding pillars in the hybrid nanorodsLED device, providing strong light extraction in a large area.

Regarding the LEDs operated at high driving current, thelight intensity distributions on the surfaces of the microholesand hybrid nanorods LEDs were acquired using a beam view


images measurement as the results demonstrated in Fig. 4(c)and (d), respectively. The driving current is at 20 mA. In thecomparison of these two types of LEDs, although the light in-tensity from the microholes is enhanced by the light scatteringand the exposed MQWs, the stronger light intensity is still ob-tained in the same locations but with the existence of nanorodsin the hybrid nanorods LED. Such a result corresponds to theL–I–V measurements as shown in Fig. 3, indicating that thenanorods in microholes exhibit the ability to extract more pho-tons and act as nano-pillars to guide light propagating at center.The light intensity distributions on the surface of the structuredLEDs also provide us the opportunities to the development ofthe future lighting components. Moreover, from the measuredresults shown in Fig. 4(a) and (c), we found that only at highinjected current, more photons could be extracted from the mi-croholes structure. Therefore, with the nanorods incorporatedin the LED device, the LEE is greatly promoted, especially atlower operation power. By designing the dimensions and den-sity of the hybrid nanorods, the light intensity distribution on ahybrid nanorods LED chip can be controlled, coordinating theother promising applications. For example, phosphors such asunevenness of the coating, we can design the phosphor-rich re-gion has a strong light extraction from the nanorods, achievinghigher conversion efficiency.

In order to investigate how the InGaN/GaN nanorods functionas light-guiding pillars to enhance the light extraction in the LEDdevices, 3D finite difference time domain simulations using theFullWAVE program were conducted to calculate the electricfield distributions and the far-field light enhancement with theexistence of nanorods [21], [32]. GaN nanorods of 450 nm indiameter were arranged in a unit-cell area of 2.8 μm × 8 μmas it performed in the experiments. The height of the nanorodswas set at 1.2 μm, while the pitch and the spacing were at750 and 300 nm, respectively. In the simulations, a z-directionelectric dipole with the radiation wavelength of 460 nm wasemployed as a light source, placed 0.4 μm below the bottomof the nanorods. The realistic material parameters and Jouleloss factors were obtained from a well-established data in Ref.[33], [34]. A simulation model of the LED structure without thenanorods was also prepared to have a comparison of the light ex-traction performance. The calculated electric field distributionsare shown in Fig. 5(a) and (b), which are represented the con-ventional and nanorods LEDs, respectively. As can be seen inthe figures, more concentrated optical energy in the light propa-gation direction can be obtained in the nanorods LED structure,indicating that the photons emitted from the MQWs are guidedby the nanorods and extracted in the longitudinal direction. Inthe simulation, we performed the established model at periodicboundary condition with a unit cell of 0.75 μm. By setting atime-dependent energy detector above 1.2 μm of the simulationmodel, the corresponding normalized light output as a functionof the simulation time is calculated and shown in Fig. 5(c),giving the relative light extraction enhancement between thenanorods and conventional LED devices. Via the calculation ofthe ratio between the steady-state light outputs of the conven-tional (black line) and nanorods (red line) LEDs, around 22%output power enhancement can be obtained in the LED devices

Fig. 5. Simulation restuls. (a) and (b) are the calculated electric field distri-butions of conventional and nanorods LEDs, respectively. (c) The comparisonof the normalized light output betwee the conventional and nanorods LEDs.(d) and (e) show the intensity mappings of the light projection in the far-fieldregion of the conventional and nanorods LEDs, respectively.

with the existence of the InGaN/GaN nanorods, correspondingto the above L–I–V measurements in Fig. 4. Furthermore, such alight extraction enhancement can also be observed in the calcu-lated far-field mapping as shown in Fig. 5(d) and (e). Regardingthe conventional LED structure, a flat surface on the top of thechips, emitted light will diverge in the far-field region, meaningthat less optical energy per unit area can be acquired. With thenanorods constructed in the LED devices, light will be guidedand propagated to the farther region with an enhancement of26.9%.

To investigate the light extraction performance in the hy-brid nanorods LEDs at different nanorods’ aspect ratios, LED


Fig. 6. The intensity–current–voltage (L–I–V) characteristics of the hybridnanorods LEDs with nanorods of 540 nm (pink), 840 nm (green) and 1.2 μm(blue) in height. The diameter of the constituent nanorods is fixed at 450 nm inthese three nanorods LEDs.

devices with nanorods of 540 nm, 840 nm and 1.2 μm were pre-pared with the same diameter of 450 nm. Different heights ofthe nanorods can be fabricated by manipulating the etching timein the ICP-RIE process. The L–I–V characteristics of these threenanorods LEDs are shown in Fig. 6. At the standard driving cur-rent of 20 mA, the forward voltages are approximately the samein these three LED chips. As long as the height of the etchednanorods do not exceed to the n-GaN layer, the electrical prop-erty would not be damaged and the I–V characteristics wouldexhibit an electric stability in these three kinds of nanorodsLEDs. Regarding the light output power, the high aspect-rationanorods offer a larger sidewall area, increasing more oppor-tunities for light escape at the GaN/air interface. Thus, highaspect-ratio nanorods at the height of 1.2 μm can provide thelight-emitting devices with a better performance at high oper-ating current, giving the feasible applications especially in thelarge power chip with the working power above 1 W.

IV. CONCLUSION

High light extraction GaN-based LEDs with a hybrid struc-ture of high aspect-ratio nanorods in microholes arrays havebeen successfully fabricated, showing an enhanced light out-put power of 22.04 mW at an operating current density of25.4 A/cm2 from the nanorods LED devices. Not only theconstituent microholes but also the well-arranged nano-rodscan further increase the LEE in the nanorods LEDs. The highaspect-ratio straight nanorods function as light guiding pillars,providing strong light extraction in a large area. Furthermore,the higher the nanorods in the LED chips, the better light ex-traction performance can be obtained at high injections currentswithout causing an electrical damage, giving the feasible ap-plications especially in the large power chip with the workingpower above 1 W. The novel nanorods light-emitting devices canbe fabricated by utilizing the NIL and the standard photolithog-raphy, giving the opportunities in reliable mass production infuture lighting industry.

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Jhih-Kai Huang received the B.S. degree fromthe National Central University, Taoyuan, Taiwan,in 2007, and the M.S. degree in Electro-OpticalEngineering from National Chiao Tung University,Hsinchu, Taiwan, in 2009. He is currently workingtoward the Ph.D. degree in the Institute of Electro-Optical Engineering, National Chiao Tung Univer-sity, Hsinchu, Taiwan. His research interests includeGaN-based device fabrication, nanoimprint technol-ogy, and nanostructure processes.

Che-Yu Liu received the B.S. degree in electrical en-gineering from National Central University, Taoyuan,Taiwan, in 2010, and the M.S. degree in photonicsfrom National Chiao Tung University, Hsinchu, Tai-wan, in 2012, respectively. He is currently workingtoward the Ph.D. degree in the Department of Pho-tonics, National Chiao Tung University, Hsinchu, Tai-wan. His research interests include the epitaxy of III–V compound semiconductor materials by MOCVDand analysis for GaN-based light-emitting diodes.

Tzi-Pei Chen received the B.S. degree in physicsfrom National Chung Hsing University, Taichung,Taiwan, in 2013. Her research areas include photolu-minescence measurement and materials analysis, op-tical simulation, and characterization for high-powerlight-emitted diodes.

Hung-Wen Huang received the M.S. and Ph.D. degrees in electrooptical en-gineering from National Chiao Tung University, Hsinchu, Taiwan, in 2003 and2007, respectively. In 2009, he joined the Research and Design Division inTSMC Solid State Lighting Corporation. His current research interests includeIII-nitride semiconductor light-emitting diodes and applications.

Fang-I Lai received the M.S. and the Ph.D. degreesfrom the Institute of Electro-Optical Engineering, Na-tional Chiao-Tung University, Hsinchu City, Taiwan,in 2001 and 2005. Since 2007, she has been with YuanZe University as a Faculty Member of the Departmentof Electrical Engineering. Her current research inter-ests include vertical cavity surface emitting lasers,blue and UV lasers and LEDs, quantum confinedoptoelectronic structures, and nanostructure applica-tions.

Po-Tsung Lee (M’06) received the B.S. degree inphysics from National Taiwan University, Taipei, Tai-wan, in 1997, and the M.S. and Ph.D. degrees fromthe University of Southern California, Los Angeles,CA, USA, in 1998, and 2003, respectively. Duringthe Ph.D. study, she was engaged in photonic crystalmicrocavity lasers.

In 2003, she joined the Institute of Electro-Optical Engineering, National Chiao Tung University(NCTU), Hsinchu, Taiwan, as an Assistant Professor.In 2007, she became an Associate Professor in the

Department of Photonics, NCTU. Her recent research interests include semi-conductor photonic crystal active and passive devices and their applications,metallic nanostructures with localized surface plasmon resonances, and silicon-based solar cell technologies. She received the University of Southern CaliforniaWomen in Science and Engineering Award in 2000–2001and the “OutstandingYoung Electrical Engineer Award” from the Chinese Institute of Electrical En-gineering in 2011.

Chung-Hsiang Lin received the B.S. and M.S. de-grees in physics from National Taiwan University,Taipei City, Taiwan. He received the M.S. degree inelectrical and computer engineering and the Ph.D.degree in physics from Polytechnic Institute of NewYork University, Brooklyn, NY, USA. He is the Pres-ident of the New Business Unit of Luxtaltek Corpo-ration, Miaoli, Taiwan, and serves as an Adjunct Pro-fessor at the Institute of Electro-Optical Engineering,National Chiao Tung University (NCTU), Hsinchu,Taiwan. He has more than ten years of experience in

the LED industry, specifically photonic crystal modeling and nanofabrication onoptoelectronic devices. He has more than 30 professional publications relatedto photonic crystal devices. Prior to joining Luxtaltek, he held several researchpositions including one as a Visiting Scholar with the Jet Propulsion Laboratory.


Chun-Yen Chang was born in Feng-Shan, Taiwan.He received the B.S. degree in electrical engineeringfrom the National Cheng Kung University (NCKU),Tainan, Taiwan, in 1960, and the M.S. and Ph.D.degrees from the National Chiao Tung University(NCTU), Hsinchu, Taiwan, in 1962 and 1969, re-spectively. He has profoundly contributed to the ar-eas of microelectronics, microwave, and optoelec-tronics, including the invention of the method oflow-pressure MOCVD using triethylgallium to fab-ricate LED, laser, and microwave devices. He pio-

neered works on Zn incorporation (1968), nitridation (1984), and fluorine in-corporation (1984) in SiO2 for ULSIs, as well as in the charge transfer insemiconductor–oxide–semiconductor systems (1968), carrier transport acrossmetal–semiconductor barriers (1970), and the theory of metal–semiconductorcontact resistivity (1971). In 1963, he joined the NCTU to serve as an In-structor, establishing a high vacuum laboratory. In 1964, he and his colleaguesestablished the nation’s first and state-of-the-art Semiconductor Research Cen-ter, NCTU, with a facility for silicon planar device processing, where theymade the nation’s first Si planar transistor in April 1965 and, subsequently, thefirst IC and MOSFET in August 1966, which strongly forms the foundationof Taiwan’s hi-tech development. From 1977 to 1987, he single-handedly es-tablished a strong electrical engineering and computer science program at theNCKU, where GaAs, α-Si, and poly-Si research was established in Taiwan forthe first time. He consecutively served as the Dean of Research (1987–1990),the Dean of Engineering (1990–1994), and the Dean of Electrical Engineeringand Computer Science (1994–1995). Simultaneously, from 1990 to 1997, heserved as the Founding President of the National Nano Device Laboratories,Hsinchu. Since August 1, 1998, he has been the President with the Institute ofElectronics, NCTU. In 2002, to establish a strong system design capability, heinitiated the “National program of system on chip,” which is based on a strongTaiwanese semiconductor foundry. He is a Member of Academia Sinica (1996)and a Foreign Associate of the National Academy of Engineering, U.S. (2000).He received the 1987 IEEE Fellow Award, the 2000 Third Millennium Medal,and the 2007 Nikkei Asia Prize for Science category in Japan and regarded as“the father of Taiwan semiconductor industries.”

Tsung Sheng Kao received the B.S. degree in physics from National CentralUniversity, Taoyuan, Taiwan in 2001, the M.S. degree in physics from NationalTaiwan University, Taipei City, Taiwan in 2004, and the Ph.D. degree from theOptoelectronics Research Centre, University of Southampton, Southampton,U. K., in 2012.

From 2013 to 2014, he was a Postdoctoral Research Fellow with the Depart-ment of Electrical and Computer Engineering, National University of Singapore,Singapore. Since early 2014, he has been an Assistant Research Fellow withthe Department of Photonics and the Institute of Electro-Optical Engineer-ing, National Chiao Tung University, Hsinchu, Taiwan. His primary researchinterests include nanooptics, superresolution imaging technology, controlledlight localization on the nanolandscapes, nonlinear optical responses of hybridnanosystems, light enhancements in plasmonic optoelectronic devices, and sur-face plasmon resonance for bio-sensing.

Hao-Chung Kuo (S’98–M’99–SM’06) received theB.S. degree in physics from the National Taiwan Uni-versity, Taipei, Taiwan, in 1990, the M.S. degree inelectrical and computer engineering from RutgersUniversity, Camden, NJ, USA, in 1995, and the Ph.D.degree in electrical and computer engineering fromthe University of Illinois at Urbana-Champaign, Ur-bana, IL, USA, in 1999. He has an extensive pro-fessional career both in research and industrial re-search institutions. From 1995 to 1997, he was aResearch Consultant with Lucent Technologies, Bell

Labs, Holmdel, NJ. From 1999 to 2001, he was an R&D Engineer with theFiber-Optics Division, Agilent Technologies. From 2001 to 2002, he was theR&D Manager with LuxNet Corporation. Since September 2002, he has been aMember of the faculty at the Institute of Electro-Optical Engineering, NationalChiao Tung University, Hsinchu, Taiwan. He has authored or coauthored morethan 60 publications. His current research interests include the epitaxy, design,fabrication, and measurement of high-speed InPand GaAs-based vertical-cavitysurface-emitting lasers, as well as GaN-based lighting-emitting devices andnanostructures.

6000107 ieee journal of selected topics in quantum ... · the residual pr layer and dielectric...

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