Browsing by Author "Lee, Wei-I"

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A Novel Technique for Growing Crack-Free GaN Thick Film by Hydride Vapor Phase Epitaxy
(2008-11-01)
Huang, Hsin-Hsiung
;
Chen, Kuei-Ming
;
Tu, Li-Wei
;
Chu, Ting-Li
;
Wu, Pei-Lun
To prevent the cracking of GaN thick films grown on a sapphire substrate by hydride vapor phase epitaxy (HVPE), a novel technique without complex processes is developed. By adding a temperature ramping step in the HVPE GaN epitaxy process, more than 300-mu m-thick high-quality crack-free GaN thick films on sapphire substrate can be obtained by this technique. After separation by a conventional laser-induced lift-off process, a 1.5 in. 300 mu m freestanding GaN wafer with a dislocation density of approximately 1 x 10(7) cm(-2) could be fabricated without any cracks. No additional designed-patterned or stress-reduced structures were applied in these samples to reduce the dislocation density and thermal stress. [DOI: 10.1143/JJAP.47.8394]
A Simple Growth Method to Produce a-Plane GaN Thick Films by Hydride Vapor Phase Epitaxy
(2013-08-01)
Wu, Yin-Hao
;
Lee, Chuo-Han
;
Chu, Chung-Ming
;
Yeh, Yen-Hsien
;
Chen, Chan-Lin
A-plane GaN was grown on r-plane sapphire using a two-step growth method by hydride vapor phase epitaxy (HVPE). In the first step, a-plane GaN formed triangular stripes along the m-direction ([(1) over bar 100] direction) at a low growth temperature. Then, increasing the growth temperature enhanced the lateral growth mode to coalesce a-plane GaN in the second step. There were triangular voids formed after growth. In this work, a new method was developed to produce the voids in the a-plane GaN film using the two-step growth method without optical lithography. (C) 2013 The Japan Society of Applied Physics
Au-Free GaN High-Electron-Mobility Transistor with Ti/Al/W Ohmic and WN (X) Schottky Metal Structures for High-Power Applications
(2016-07)
Hsieh, Ting-En
;
Lin, Yueh-Chin
;
Chu, Chung-Ming
;
Chuang, Yu-Lin
;
Huang, Yu-Xiang
In this study, an Au-free AlGaN/GaN high-electron-mobility transistor (HEMT) with Ti/Al/W ohmic and WNx Schottky metal structures is fabricated and characterized. The device exhibits smooth surface morphology after metallization and shows excellent direct-current (DC) characteristics. The device also demonstrates better performance than the conventional HEMTs under high voltage stress. Furthermore, the Au-free AlGaN/GaN HEMT shows stable device performance after annealing at 400A degrees C. Thus, the Ti/Al/W ohmic and WN (X) Schottky metals can be applied in the manufacturing of GaN HEMT to replace the Au based contacts to reduce the manufacturing costs of the GaN HEMT devices with comparable device performance.
Comparison between extended microtunnels along different crystal orientations in GaN
(2008)
Wu, Pei-Lun
;
Huang, Hsin-Hsiung
;
Zeng, Hung-Yu
;
Liu, Po-Chun
;
Lai, Chih-Ming
Triangular prism-like extended microtunnels (EMTs) can be easily formed in specially designed cpitaxial lateral overgrowth GaN thick films by selective wet chemical etching in molten potassium hydroxide (KOH), In this study, extended microtunnels along the < 1100 > and the < 1120 > directions were fabricated and compared. If tunnels along the < 1100 > direction, the (1122) planes would be the etch stop plane. While the tunnels along < 1120 > direction, the etch stop plane would become to (1011) planes. The activation energies of wet chemical etch for the {1122} planes and the (1011) planes were determined to be 23.6 kcal/mol (1.02 eV) and 22.8 kcal/mol (0.99 eV) using Arrhenius plot. On the other hand, the etching depths of the tunnels along the < 1100 > direction were more than twice the depths of the tunnels along the < 1120 > direction during the same etching time. The highest etch rate of the tunnels along the axial direction can reach 1000 mu m/hr in < 1100 > direction, which is believed to be the highest etch rate of GaN ever reported. Additional crystal facet of m-plane in GaN was also observed in the sample with extended microtunnels along the < 1120 > direction. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Effective reduction of bowing in free-standing GaN by N-face regrowth with hydride vapor-phase epitaxy
(2009-05-01)
Chen, Kuei-Ming
;
Huang, Hsin-Hsiung
;
Kuo, Yi-Lin
;
Wu, Pei-Lun
;
Chu, Ting-Li
Free-standing GaN films prepared with hydride vapor-phase epitaxy (HVPE) technique usually show bowing resulting from the high densities of defects near the N-polar face after separation from the original substrates. To solve the problem, a simple technique has been developed. A GaN layer was regrown on the N-polar face of the free-standing GaN by HVPE. High-resolution X-ray diffraction (HRXRD) measurements were performed to compare the bowings among GaN films before laser lift-off (LLO), after LLO, and after regrowth. The apparent reductions of XRD full-width at half-maximum (FWHM), along with the increase of XRD peak intensity, after regrowth clearly demonstrate the effectiveness of this method to eliminate bowings of the free-standing GaN films. (C) 2009 Elsevier B.V. All rights reserved.
Effects of strained InGaN interlayer on contact resistance between p-GaN and indium tin oxide
(2007-04-30)
Lee, Chi-Ling
;
Lee, Wei-I
;
電子物理學系
;
Department of Electrophysics
Indium tin oxide (ITO), with its transparency and strong adhesion to GaN, has been used as a replacement for Ni/Au as a contact on p-GaN. However, ITO suffers from high contact resistance on p-GaN. In this work, low contact resistance between ITO and the p-GaN layer was consistently achieved using various strained InGaN layers as the interface layers between ITO and p-GaN layer. The doping of InGaN, whether n type or p type, has a relatively weak effect on the contact resistance as long as the thickness of the InGaN layer is adequately controlled. The secondary-ion-mass spectroscopy depth profile reveals that the n-type InGaN strained contact layer was also heavily doped with Mg. Results of this study demonstrate that the piezoelectric field between InGaN and p-GaN is important in reducing the barrier height of Ohmic contact. (c) 2007 American Institute of Physics.
Etching method for nitride semiconductor
(2009-03-05)
Lee, Wei-I
;
Huang, Hsin-Hsiung
;
Zeng, Hung-Yu
The invention discloses etching method for the nitride semiconductor. Firstly dielectric layer is formed on gallium nitride. The line pattern or dot pattern is formed on the dielectric layer by using the exposure, development, and etching processes. The dielectric layer is used as the mask for the epitaxial lateral overgrowth of follow-up gallium nitride layer. The thick gallium nitride film is grown on the dielectric layer. Then the wet etching process is used to remove the dielectric layer, and the thick gallium nitride film on the dielectric layer is etched to form the specific shape as required.
Extended microtunnels in GaN prepared by wet chemical etch
(2006-11-13)
Huang, Hsin-Hsiung
;
Zeng, Hung-Yu
;
Lee, Chi-Ling
;
Lee, Shih-Chang
;
Lee, Wei-I
It is demonstrated in GaN that microtunnels extended beyond hundreds of microns can be easily achieved using wet chemical etch. To obtain this result, specially designed structures of GaN layers are first grown on sapphire substrates with metal-organic chemical vapor deposition and subsequently with hydride vapor phase epitaxy techniques. The prepared samples are then chemically etched in molten KOH. With the designed structure of GaN layers, extended microtunnels with triangular cross sections are formed. The crystallographic planes of the triangular bevels belong to the {11(2) over bar 2} family. The etch rate of the tunnel can be as high as 10 mu m/min at proper etching conditions. (c) 2006 American Institute of Physics.
Formation of nitride laser cavities with cleaved facets on transferred laser diodes on GaAs substrates
(2008)
Yu, Wen-Chien
;
Ye, Shu-Mei
;
Hsiao, Feng-Ke
;
Lee, Chi-Ling
;
Lee, Wei-I
Smoothly cleaved facets with high reflectivities have been demonstrated on GaN laser diodes after the devices were transferred onto GaAs substrates. The GaN based laser diode structure was first fabricated by metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. The samples were then mounted onto thin GaAs substrates using wafer-bonding technology. Laser lift-off (LLO) technique was applied to remove the original sapphire substrate and transfer the GaN laser structure onto GaAs substrates. Since the cubic substrates have well-defined laser cavity cleavage facet, the GaN structures bonded onto the substrates also formed smooth facets after cleavage. The cleaved facets of GaN laser diodes have been characterized using atomic force microscopy (AFM) with less than 2 nm roughness. The present study demonstrated the feasibility of transferring GaN laser structures onto other more appealing substrates for formation of laser cavities.
Free-standing a-plane GaN substrates grown by HVPE
(2012)
Wu, Yin-Hao
;
Yeh, Yen-Hsien
;
Chen, Kuei-Ming
;
Yang, Yu-Jen
;
Lee, Wei-I
A-plane free-standing GaN was grown on a-plane GaN templates by HVPE. A-plane GaN templates were grown on r-plane sapphire by MOCVD with multilayer high-low-high temperature AlN buffer layers. A regrowth method was used for growing GaN through HVPE. First, GaN was grown on a-plane GaN templates, followed by separating the a-plane GaN film from r-plane sapphire using LLO. Then, the GaN films were regrown using HVPE. The resulting free-standing GaN contained some voids, which causes to release the stress.
High performance 380-nm ultraviolet light-emitting-diodes with 3% efficiency droop by using free-standing GaN substrate manufacturing from GaAs substrate
(2014-07-07)
Shieh, Chen-Yu
;
Tsai, Ming-Ta
;
Li, Zhen-Yu
;
Kuo, Hao-Chung
;
Chang, Jeng-Yang
We investigated the influence of free-standing GaN (FS-GaN) substrates on the performance of ultraviolet light-emitting-diodes (UV-LEDs) grown on top by atmospheric pressure metal-organic chemical vapor deposition. High-resolution double-crystal x-ray diffraction (HRDCXD) analysis demonstrated high-order satellite peaks and clear fringes between them for UV-LEDs grown on the FS-GaN substrate, from which the interface roughness was estimated. In addition, the full width at half maximum of the HRDCXD rocking curve in the (0002) and the (1012) reflections were reduced to below 90 arc sec. The Raman results indicated that the GaN-based epilayer of strain free was grown. Additionally, the effect of the FS-GaN substrate on the crystal quality of the UV-LEDs was examined in detail by transmission electron microscopy (TEM). The TEM characterizations revealed no defects and V-pits were found in the scanned area. Based on the results mentioned above, the light output power of UV-LEDs on the FS-GaN substrate can be enhanced drastically by 80% and 90% at 20 and 100 mA, respectively. Furthermore, an ultralow efficiency degradation of about 3% can be obtained for the UV-LEDs on the FS-GaN substrate at a high injection current. The use of an FS-GaN substrate is suggested to be effective for improving the emission efficiency and droop of UV-LEDs grown thereon.
High-efficiency and low assembly-dependent chip-scale package for white light-emitting diodes
(2015-04-21)
Huang, Che-Hsuan
;
Chen, Kuo-Ju
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Tsai, Ming-Ta
;
Shih, Min-Hsiung
;
Sun, Chia-Wei
This article presents a chip-scale package (CSP) with conformal and uniform structures for white light-emitting diodes used in lighting and backlight unit (BLU) applications. The CSP structures produce higher light extraction efficiency and lower assembly-dependent packaging compared with conventional surface-mounted devices (SMDs). Simulation results show that compared with SMDs, the luminous efficiency of CSP structures is 8.81% higher in lighting applications and 9.43% higher in BLU applications. This is likely due to light loss in the light bowl of the SMDs. Moreover, CSPs with a conformal phosphor structure exhibit low assembly dependence and redundancy, and rb-CSPs with a conformal structure are a more effective light source in both lighting and BLU applications. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
High-Quality Free-standing GaN Thick-films Prepared by Hydride Vapor Phase Epitaxy using Stress Reducing Techniques
(2009)
Huang, Hsin-Hsiung
;
Lee, Wei-I
;
Chen, Kuei-Ming
;
Chu, Ting-Li
;
Wu, Pei-Lun
As one of the most mature techniques for manufacturing free-standing GaN substrates, hydride vapor phase epitaxy (HVPE) always encounters problems associated with residue thermal stress, such as GaN bending and cracking during and after growth. This work presents a patterning approach and a non-patterning approach to reduce stress in thick GaN films grown on sapphires by HVPE. The patterning approach, forming dot air-bridged structures, adopted standard photolithography to fabricate hexagonally aligned patterns of dots on GaN templates. Following HVPE growth, regular voids were formed and buried in the GaN thick-films. These voids helped to relax the stress in the GaN thick-films. In the non-patterning approach, thick GaN films were simply grown at a specially set sequence of ramping temperatures during HVPE growth without any patterned structure. This temperature-ramping technique, gives crack-free high-quality 2"-diameter GaN films, thicker than 250 mu m, on sapphires in high yields. These thick GaN films can be separated from sapphire using conventional laser-induced lift-off processes, which can be followed by subsequent HVPE regrowths. A 600 mu m-thick free-standing GaN films has a typical dislocation density of around 4x10(6) cm(-2) with a full width at half maximum (FWHM) in the high resolution X-ray diffraction (HRXRD) spectrum of GaN (002) of around 150 arcsec. The residual stress in the thick GaN films was analyzed by micro-Raman spectroscopy. The effectiveness of the patterning and the non-patterning techniques in reducing the strain in GaN films is discussed. The advantages and weaknesses of the patterning and the non-patterning techniques will be elucidated.
Hydrogen etch of GaN and its application to produce porous GaN caves
(2011)
Yeh, Yen-Hsien
;
Hsu, Ying-Chia
;
Wu, Yin-Hao
;
Chen, Kuei-Ming
;
Lee, Wei-I
Although it is known that GaN tend to decompose in hydrogen environments, there has been few investigations in hydrogen etch of GaN. This study performs a systematic research on hydrogen etch of GaN under various pressures. It is observed that hydrogen atoms initially etch into GaN to form pinholes. Dislocations are usually the preferred places for initial hydrogen etch, but not all etched holes result from dislocations. When etched at low pressure and high temperature, deep vertical holes extending several microns can be formed by the hydrogen etch. However, when etch is performed at high pressure, apparent lateral etch are observed under the initial holes, leading to bollard-like GaN posts. From this systematic study, a model has been proposed to explain the vertical and the lateral etching mechanisms. With the established model, a sequential etch of GaN in hydrogen under varying pressure has been designed to successfully maintain a smooth GaN front surface, but to etch the underlying GaN to form a porous cave structure. Thick GaN films are then overgrown on such GaN layers with the hydride vapor phase epitaxy technology. It is demonstrated that the overgrown GaN thick films can self-separate from the underlying Al(2)O(3) substrates.
Hydrogen etching of GaN and its application to produce free-standing GaN thick films
(2011-10-15)
Yeh, Yen-Hsien
;
Chen, Kuei-Ming
;
Wu, Yin-Hao
;
Hsu, Ying-Chia
;
Yu, Tzu-Yi
This work investigates the morphology of GaN etched in hydrogen (H(2)) at different temperatures, the activation energies of the rate-limiting steps of H(2) etching, and the overgrowth on a H(2)-etched GaN template. The surfaces of GaN have different profiles after being etched in H(2); they resemble a plane decorated with columns and mooring posts in a low-temperature etching condition, and with deep cavities in a high-temperature etching condition. The etched profiles show that H(2) etching has controllable etching directions: vertical and lateral. In a low-temperature condition, H(2) etching has both vertical and lateral etching directions; however, in a high-temperature condition, it has only the vertical etching direction. The activation energies of the rate-limiting steps under etching pressures of 100 and 700 Torr are estimated to be 3.22 and 3.77 eV, respectively. A thick GaN layer has been grown on a H2-etched GaN template, and it has self-separated from the underlying sapphire substrate. (C) 2011 Elsevier B.V. All rights reserved.
Hydrogen etching on the surface of GaN for producing patterned structures
(2011-01-01)
Yeh, Yen-Hsien
;
Chen, Kuei-Ming
;
Wu, Yin-Hao
;
Hsu, Ying-Chia
;
Lee, Wei-I
The morphology of GaN etched in hydrogen atmosphere is investigated. It is found that GaN surfaces have different profiles after being etched at different pressures. The profile resembles a surface that has been decorated with columns or mooring posts at high pressure and with deep cavities at low pressure. Etch pit density (EPD) experiment shows all dislocations have been etched to form cavities at low pressure, but not all the cavities result from etched dislocations. A model has been developed to explain the mechanism of H(2) etching. Patterned structure with a flat surface and porous inside has been produced by two-step etching which is designed according to the model. (C) 2010 Elsevier B.V. All rights reserved.
Investigations of GaN growth on the sapphire substrate by MOCVD method with different AlN buffer deposition temperatures
(2016-04)
Huang, Wei-Ching
;
Chu, Chung-Ming
;
Wong, Yuen Yee
;
Chen, Kai-Wei
;
Lin, Yen-Ku
The effects of different AlN buffer deposition temperatures on the GaN material properties grown on sapphire substrate was investigated. At relatively higher AlN buffer growth temperature, the surface morphology of subsequent grown GaN layer was decorated with island-like structure and revealed the mixed-polarity characteristics. In addition, the density of screw TD and leakage current in the GaN film was also increased. The occurrence of mixed-polarity GaN material result could be from unintentional nitridation of the sapphire substrate by ammonia (NH3) precursor at the beginning of the AlN buffer layer growth. By using two-step temperature growth process for the buffer layer, the unintentional nitridation could be effectively suppressed. The GaN film grown on this buffer layer exhibited a smooth surface, single polarity, high crystalline quality and high resistivity. AlGaN/GaN high electron-mobility transistor (HEMT) devices were also successfully fabricated by using the two-step AlN buffer layer. (C) 2016 Elsevier Ltd. All rights reserved.
MANUFACTURE METHOD OF MULTILAYER STRUCTURE HAVING NON-POLAR A-PLANE III-NITRIDE LAYER
(2010-08-05)
Lee, Wei-I
;
Chen, Jenn-Fang
;
Chiang, Chen-Hao
A manufacture method of a multilayer structure having a non-polar a-plane {11-22} III-nitride layer includes forming a nucleation layer on a r-plane substrate, wherein the nucleation layer is composed of multiple nitride layers; and forming a non-polar a-plane {11-20} III-nitride layer on the nucleation layer. The nucleation layer features reduced stress, reduced phase difference of lattice, blocked elongation of dislocation, and reduced density of dislocation. Thus, the non-polar a-plane {11-20} III-nitride layer with flat surface can be formed.
Method for modulating the wafer bow of free-standing GaN substrates via inductively coupled plasma etching
(2010-12-01)
Chen, Kuei-Ming
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Yeh, Yen-Hsien
;
Wu, Yin-Hao
;
Chiang, Chen-Hao
;
Yang, Din-Ru
The bowing curvature of the free-standing GaN substrate significantly decreased almost linearly from 067 to 0 056 m(-1) (i e the bowing radius increased from 1 5 to 178 m) with increase in inductively coupled plasma (ICP) etching time at the N-polar face and eventually changed the bowing direction from convex to concave Furthermore the Influences of the bowing curvature on the measured full width at half maximum (FWEIM) of high-resolution X-ray diffraction (HRXRD) in (0 0 2) reflection were also deduced which reduced from 176 8 to 888 arcsec with increase in ICP etching time Decrease in the nonhomogeneous distribution of threading dislocations and point defects as well as V(Ga)-O(N) complex defects on removing the GaN layer from N-polar face which removed large amount of defects was one of the reasons that improved the bowing of the free-standing GaN substrate Another reason was the high aspect ratio of needle-like GaN that appeared at the N-polar face after ICP etching which released the compressive strain of the free-standing GaN substrate By doing so crack-free and extremely flat free-standing GaN substrates with a bowing radius of 178 m could be obtained (C) 2010 Elsevier B V All rights reserved
Microscopic evidence for the dissociation of water molecules on cleaved GaN(1(1)over bar00)
(2018-01-14)
Wu, Shih-Yu
;
Lang, Liang-Wei
;
Cai, Pei-Yang
;
Chen, Yun-Wen
;
Lai, Yu-Ling
The dissociation of water molecules absorbed on a cleaved non-polar GaN(1(1)over bar00) surface was studied primarily with synchrotron-based photoemission spectra and density-functional-theory calculations. The adsorbed water molecules are spontaneously dissociated into hydrogen atoms and hydroxyl groups at either 300 or 130 K, which implies a negligible activation energy (<11 meV) for the dissociation. The produced H and OH were bound to the surface nitrogen and gallium on GaN(1(1)over bar00) respectively. These results highlight the promising applications of the non-polar GaN(1(1)over bar00) surface in water dissociation and hydrogen generation.