H.W. Huang

National Tsing Hua University, Hsin-chu-hsien, Taiwan, Taiwan

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Publications (54)

  • [Show abstract] [Hide abstract] ABSTRACT: In this paper, we demonstrated the high performance GaN-based LEDs by using a high aspect ratio cone-shape nano-patterned sapphire substrate (HAR-NPSS). We utilized nano-imprint lithography (NIL) and dry-etching system to fabricate a high depth HAR-NPSS. The micro-scale patterned sapphire substrate (PSS) was also used for comparison. A great enhancement of light output was observed when GaN-based LEDs were grown on a HAR-NPSS or a PSS. The light output power of LEDs with a HAR-NPSS and LEDs with a PSS were enhanced of 49 and 38% compared to LEDs with a unpatterned sapphire substrate. The high output power of the LED with a HAR-NPSS indicated that the technology of NAR-NPSS not only can improve the crystalline quality of GaN-based LEDs but also a promising development to a NPSS.
    Article · Dec 2013 · Journal of Display Technology
  • J.K. Huang · D.W. Lin · C.Y. Lee · [...] · H.C. Kuo
    Conference Paper · Jan 2013
  • Chien-Chung Lina · Ching-Hsueh Chiu · H.W. Huang · [...] · Chun-Yen Chang
    [Show abstract] [Hide abstract] ABSTRACT: Highly efficient InGaN-base light emitting diodes are crucial for next generation solid state lighting. However, drawbacks in substrate materials such as lattice and thermal expansion coefficient mismatches hold back the lamination efficiency improvement. In the past, patterned sapphire sustrate (PSS) has been proven to be effect to enhance the LED's performance. In this work, we reviewed several promising nano-scale technologies which successfully increase the output of LED through better material quality and light extraction. First, we presented a study of high-performance blue emission GaN LEDs using GaN nanopillars (NPs). It exhibits smaller blue shift in electroluminescent peak wavelength and great enhancement of the light output (70% at 20 mA) compared with the conventional LEDs. Secondly, GaN based LEDs with nano-hole patterned sapphire (NHPSS) by nano-imprint lithography are fabricated structure grown on sapphire substrate. At an injection current of 20mA, the LED with NHPSS increased the light output power of LEDs by 1.33 times, and the wall-plug efficiency is 30% higher at 20mA indicating that it had larger light extraction efficiency (LEE). Finally, we fabricated the high performance electrical pumping GaN-based semipolar {10–11} nano-pyramid LEDs on c-plane sapphire substrate by selective area epitaxy (SAE). The emission wavelength only blue-shifted about 5nm as we increased the forward current from 40 to 200mA, and the quantum confine stark effect (QCSE) had been remarkably suppressed on semipolar surface at long emission wavelength region. These results manifest the promising role of novel nanotechnology in the future III-nitride light emitters.
    Article · Nov 2011 · Proceedings of SPIE - The International Society for Optical Engineering
  • Jin-Wei Shi · F.-M. Kuo · H.-W. Huang · [...] · Ming-Lung Lee
    [Show abstract] [Hide abstract] ABSTRACT: In this letter, the mechanism for improvement of the dynamic performance of GaN-based light-emitting diodes with an InGaN insertion layer is investigated using the very fast electrical-optical pump-probe technique. Our measurements indicate that, when the bias current is relatively low (100 A/cm<sup>2</sup>), the device with the InGaN insertion layer (device A) exhibits a shorter response time than does the control (device B) without such a layer. However, when the bias current density reaches 0.5 kA/cm<sup>2</sup>, devices A and B exhibit exactly the same response time during operation from room temperature to 200 <sup>°</sup>C. These results indicate that, under low current density (100 A/cm<sup>2</sup>), the piezoelectric (PZ) field inside device A will be stronger, which should result in a lower effective barrier height with a shorter carrier escape time than is the case for device B. On the other hand, under high bias current density, both devices have the same internal response time, which indicates the screening of the PZ field inside due to injected carriers. These dynamic measurement results suggest that the origin of the efficiency droop in our device under low and high bias current densities is carrier leakage and the Auger effect, respectively.
    Article · Jun 2011 · IEEE Electron Device Letters
  • Jin-Wei Shi · H.-W. Huang · F.-M. Kuo · [...] · Jinn-Kong Sheu
    [Show abstract] [Hide abstract] ABSTRACT: For the first time, the internal carrier dynamic inside GaN-based green light-emitting diodes (LEDs) during operation has been directly observed using the demonstrated electrical-optical pump-probe technique. Short electrical pulses (~100 ps) were pumped into high-speed cascade green LEDs, and the output optical pulses were probed using high-speed photoreceiver circuits. Using such a method, the recombination time constant of the carriers can be directly measured without any assumption about the recombination process. A high-speed cascade LED structure was adopted in the experiments to eliminate the influence of the RC delay time on the measured responses. Our measurement results indicate that both single- and three-LED cascade structures have the same internal response time due to current continuity. Furthermore, based on responses measured under different temperatures (from 25°C to 200°C), the origin of the efficiency droop in GaN-based green LEDs under a high bias current density may be attributed to the strong nonradiative Auger effect rather than device heating or carrier overflow. The demonstrated measurement scheme and high-speed cascade device structure offer a novel and simple way to straightforwardly investigate the internal carrier dynamic inside the active layers of the LED during forward-bias operation.
    Article · Mar 2011 · IEEE Transactions on Electron Devices
  • H. W. Huang · Fang-I. Lai · S. Y. Kuo · [...] · K. Y. Lee
    [Show abstract] [Hide abstract] ABSTRACT: GaN-based LEDs with photonic crystal (PhC) patterns on an n- and a p-GaN layer by nano-imprint lithography (NIL) are fabricated and investigated. At a driving current of 20 mA on Transistor Outline (TO)-can package, the light output power of the GaN-based LED with PhC patterns on an n- and a p-GaN layer is enhanced by a factor of 1.30, and the wall-plug efficiency is increased by 24%. In addition, the higher output power of the LED with PhC patterns on the n- and p-GaN layer is due to better crystal quality on n-GaN and higher scattering effect on p-GaN surface using PhC pattern structure.
    Article · Feb 2011 · Solid-State Electronics
  • C.K. Tseng · H.W. Huang · J.R. Huang · [...] · M.C.M. Lee
    [Show abstract] [Hide abstract] ABSTRACT: A silicon-based resonant cavity light emitting diode is presented in this paper. Via the microcavity effect, the electroluminescence spectrum is significantly reduced and the emission intensity is enhanced, showing the potential of silicon lighting devices.
    Article · Nov 2010
  • H W Huang · K Y Lee · J K Huang · [...] · H C Kuo
    [Show abstract] [Hide abstract] ABSTRACT: In this paper, GaN-based LEDs with a SiO2 photonic quasi-crystal (PQC) pattern on an n-GaN layer by nano-imprint lithography (NIL) are fabricated and investigated. At a driving current of 20 mA on Transistor Outline (TO)-can package, the better light output power of LED III (d = 1.2 microm) was enhanced by a factor of 1.20. After 1000 h life test (55 degrees C/50 mA) condition, Normalized output power of LED with a SiO2 PQC pattern (LED III (d = 1.2 microm)) on an n-GaN layer only decreased by 5%. This results offer promising potential to enhance the light output power of commercial light-emitting devices using the technique of nano-imprint lithography.
    Article · Oct 2010 · Journal of Nanoscience and Nanotechnology
  • J. K. Huang · H. W. Huang · K. Y. Lee · H. C. Kuo
    Conference Paper · Sep 2010
  • Jin-Wei Shi · H.-W. Huang · F.-M. Kuo · [...] · M.L. Lee
    [Show abstract] [Hide abstract] ABSTRACT: We demonstrate a novel type of linear cascade green light-emitting diode (LED) arrays as a light source for in-car or harsh environment plastic optical fiber (POF) communications. To further enhance its dynamic and static performance, an InGaN layer is inserted between an n-type GaN cladding layer and InGaN-GaN multiple quantum wells as an efficient current spreading layer. Compared with the control device without that layer, our three-LED cascade array demonstrates a smaller turn-on voltage (9.3 versus 11 V at 20 mA) and a larger output power (25.5 versus 22.5 mW at 180 mA), corresponding to an enhancement of around 31% in wall-plug efficiency. Furthermore, under the constant voltage bias of an in-car battery (12 V), our three-LED array exhibits an electrical-to-optical 3-dB bandwidth (100 versus 40 MHz) performance superior to that of the control device. Even under high-temperature dynamic operation, we observe that the InGaN insertion layer gives strong enhancement of modulation speed with negligible degradation of the output power, unlike the red resonant-cavity LEDs conventionally used for POF. We achieve 200-Mb/s error-free transmission at 200°C which is the highest operation temperature among all the reported high-speed LEDs.
    Article · Aug 2010 · IEEE Photonics Technology Letters
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    H.W. Huang · J.K. Huang · K.Y. Lee · [...] · H.C. Kuo
    [Show abstract] [Hide abstract] ABSTRACT: GaN-based LEDs with a SiO<sub>2</sub> oxide PQC pattern on an n-GaN layer by nanoimprint lithography are fabricated and investigated. At a driving current of 20 mA on a Transistor-Outline-can package, the light output power of LED III (d = 1.2 μm) was enhanced by a factor of 1.20. The internal-quantum-efficiency result offers promising potential to enhance the light output power of commercial light-emitting devices with a SiO<sub>2</sub> oxide PQC structure on an n-GaN layer.
    Full-text available · Article · Jul 2010 · IEEE Electron Device Letters
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    H.W. Huang · J.K. Huang · C.H. Lin · [...] · H.C. Kuo
    [Show abstract] [Hide abstract] ABSTRACT: The enhancement of light extraction from GaN-based light-emitting diodes (LEDs) with a patterned sapphire substrate (PSS) and a SiO<sub>2</sub> 12-fold photonic quasi-crystal (PQC) structure using nanoimprint lithography is presented. At a driving current of 20 mA on transistor-outline-can package, the light output powers of LED with a PSS and LED with a PSS and a SiO<sub>2</sub> PQC structure are enhanced by 35% and 48%, compared with the conventional LED. In addition, the higher output power of the LED with a PSS and a SiO<sub>2</sub> PQC structure is due to better reflectance on PSS and higher epitaxial quality on an n-GaN using a SiO<sub>2</sub> 12-fold PQC structure pattern. These results provide promising potential to increase output powers of commercial light-emitting devices.
    Full-text available · Article · Jul 2010 · IEEE Electron Device Letters
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    H W Huang · F I Lai · J K Huang · [...] · H C Kuo
    [Show abstract] [Hide abstract] ABSTRACT: GaN (gallium nitride)-based light-emitting diodes (LEDs) with a nano-scale SiO 2 structure between a transparent indium-tin oxide (ITO) layer and p-GaN were fabricated. The forward voltage at 20 mA for a GaN-based LED with a SiO 2 nano-scale structure was slightly higher than that of a conventional GaN-based LED because the total area of the p-type metal contact between the transparent ITO layer and p-GaN was smaller. However, the light output power for the GaN-based LED with a nano-scale structured SiO 2 at 20 mA was 24% higher than that for a conventional GaN-based LED structure. This increase in the light output power is mostly attributed to the scattering of light from the SiO 2 photonic quasi-crystal (PQC) layer.
    Full-text available · Article · Jun 2010 · Semiconductor Science and Technology
  • J.-W. Shi · H.-W. Huang · F.-M. Kuo · [...] · J.-K. Sheu
    [Show abstract] [Hide abstract] ABSTRACT: We demonstrate cascade green light-emitting-diodes, which greatly release trade-off between output-power and speed and exhibits strong modulation-speed enhancement with negligible output-power degradation from room-temperature to 200°C operation. 200 Mbit/sec error-free transmission at 200°C can be achieved.
    Conference Paper · Apr 2010
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    H. W. Huang · C.H. Lin · J. K. Huang · [...] · S. C. Wang
    [Show abstract] [Hide abstract] ABSTRACT: In this paper, gallium-nitride (GaN)-based light-emitting diodes (LEDs) with nano-hole patterned sapphire (NHPSS) by nano-imprint lithography are fabricated and investigated. At an injection current of 20 mA, the LED with NHPSS increased the light output power of the InGaN/GaN multiple quantum well LEDs by a factor of 1.33, and the wall-plug efficiency is 30% higher at 20 mA indicating that the LED with NHPSS had larger light extraction efficiency. In addition, by examining the radiation patterns, the LED with NHPSS shows stronger light extraction with a wider view angle. These results offer promising potential to enhance the light output powers of commercial light-emitting devices using the technique of nano-imprint lithography.
    Full-text available · Article · Aug 2009 · Materials Science and Engineering B
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    H W Huang · C H Lin · K Y Lee · [...] · S C Wang
    [Show abstract] [Hide abstract] ABSTRACT: GaN-based thin-film vertical-injection light-emitting diodes (VLEDs) with a 12-fold photonic quasi-crystal (PQC) by nano-imprint lithography (NIL) are fabricated and presented. At a driving current of 20 mA and with a chip size of 350 µm × 350 µm, the light output power of our thin-film LED with a 12-fold PQC structure reaches 41 mW. This result is an enhancement of 78% when compared with the output power of a VLED without a PQC structure. In addition, the corresponding light radiation pattern shows a narrower beam shape due to the strong guided light extraction effect by the formed PQC structure in the vertical direction.
    Full-text available · Article · Jul 2009 · Semiconductor Science and Technology
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    Shi-Hao Guol · H.-W. Huang · C.-S. Lin · [...] · Jin-Wei Shi
    [Show abstract] [Hide abstract] ABSTRACT: In this research, we demonstrate array of transverse-junction (TJ) blue light-emitting-diodes (LEDs), which are specified as a horizontal carrier flow instead of side-by-side injection, with a consequence of InxGa1-xN/GaN multiple-quantumwells (MQWs) as the active region. The demonstrated devices were carried out by the re-growth of n-type GaN on the sidewall of p-type GaN. Regarding the transverse carrier flow of injected carriers, these TJ-LEDs, as compared to the control related to traditional vertical junction structure, can effectively spread injected currents more uniformly, minimize the problem of nonuniform carrier-distribution and current crowding effect, and achieve 35% improvement of power performance.
    Full-text available · Article · Feb 2009 · Proceedings of SPIE - The International Society for Optical Engineering
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    H W Huang · C H Lin · C C Yu · [...] · S C Wang
    [Show abstract] [Hide abstract] ABSTRACT: Enhancements of light extraction of GaN-based power chip (PC) LEDs with and without rough surface on p-GaN and TiO2/SiO2 omnidirectional reflector (ODR) on the bottom are presented. Motivated by phosphor-conversion white light applications, the peak-emitting wavelength of our studied PC LEDs is chosen to be 455 nm and the fabricated ODR is designed for the same wavelength regime. At a driving current of 350 mA and a chip size of 1 mm × 1 mm on a TO-can package, the light output power of the PC LED with ODR on the bottom and pit type of rough surface on p-GaN is enhanced by 67% when compared with the same device without ODR and rough surface. Furthermore, by examining the radiation patterns, the PC LED with the ODR and rough surface shows stronger enhancement around the vertical direction. Our results provide promising potential to increase output powers of commercial light emitting devices, especially for white light applications.
    Full-text available · Article · Oct 2008 · Semiconductor Science and Technology
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    H.W. Huang · C.H. Lin · C.C. Yu · [...] · S.C. Wang
    [Show abstract] [Hide abstract] ABSTRACT: The GaN-based thin-film vertical-injection LEDs (VLEDs) with GaN nano-cone structures are fabricated and presented. Under the process conditions of fixed Cl2/Ar flow rate of 10/25sccm and ICP/bias power of 200/200W, the GaN nano-cone structures are self-assembly formed with variable density of 1.5×107 to 1.4×109cm−2 and variable depth of 0.56–1.34μm when varying the ICP chamber pressure. At a driving current of 350mA and with chip size of 1mm×1mm, the light output power of our thin-film LED with a specific GaN nano-cone structure reaches 224mW which is enhanced by 160% when compared with the output power of conventional VLED. In addition, the corresponding light radiation pattern shows much higher light intensity due to the strong light scattering effect by the formed nano-cone structure.
    Full-text available · Article · Jul 2008 · Materials Science and Engineering B
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    [Show abstract] [Hide abstract] ABSTRACT: We have developed a simple method to fabricate nanoscale masks by using self-assembly Ni clusters formed through a rapid thermal annealing (RTA) process. The density and dimensions of the Ni nano-masks could be precisely controlled. The nano-masks were successfully applied to GaN-based light-emitting diodes (LEDs) with nano-roughened surface, GaN nanorods, and GaN-based nanorod LEDs to enhance light output power or change structure properties. The GaN-based LED with nano-roughened surface by Ni nano-masks and excimer laser etching has increased 55% light output at 20 mA when compared to that without the nano-roughened process. The GaN nanorods fabricated by the Ni nano-masks and ICP-RIE dry etching showed 3.5 times over the as-grown sample in photoluminescence (PL) intensity. The GaN-based nanorod LEDs assisted by photo-enhanced chemical (PEC) wet oxidation process were also demonstrated. The electroluminescence (EL) intensity of the GaN-based nanorod LED with PEC was about 1.76 times that of the as-grown LED. The fabrication, structure properties, physical features, and the optical and electrical properties of the fabricated devices will be discussed.
    Full-text available · Article · Jul 2008 · Journal of Lightwave Technology