Browsing by Author "Chen, Kuei-Ming"

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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]
Effective reduction of bowing in free-standing GaN by N-face regrowth with hydride vapor-phase epitaxy
(2009-05-01)
Chen, Kuei-Ming
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Huang, Hsin-Hsiung
;
Kuo, Yi-Lin
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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.
Free-standing a-plane GaN substrates grown by HVPE
(2012)
Wu, Yin-Hao
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Yeh, Yen-Hsien
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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-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.
Homoepitaxy on GaN substrate with various treatments by metalorganic vapor phase epitaxy
(2011-03-01)
Chen, Kuei-Ming
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Wu, Yin-Hao
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Yeh, Yen-Hsien
;
Chiang, Chen-Hao
;
Chen, Kuei-You
This study shows the morphological, optical, and crystal characteristics of homoepitaxial GaN epilayers that were overgrown by metalorganic vapor phase epitaxy (MOVPE) on the Ga-polar face of GaN substrates that had undergone various surface treatments. The MOVPE overgrown epilayer with surface treatment was fine polished (sample C) to obtain a flat surface that exhibits two-dimensional step-flow growth. And the interface between the MOVPE overgrown epilayer and the GaN substrate was completely absent, indicating the continuous growth of GaN, and, correspondingly, the high degree of homoepitaxy. However, a network of cracks appeared in as-grown sample A (mechanically polished) and hillocks formed with the striped morphology in as-grown sample B (ICP treated). The dislocation density and full width at half maximum (FWHM) obtained by X-ray measurements of as-grown sample C were superior to those obtained by other surface treatments and the original GaN substrate. According to the photoluminescence (PL) and cathodoluminescence (CL) measurements, the decreasing FWHM of band edge emission (NBE) of the overgrown epilayers was attributable to the point defects of V(N) being greatly reduced. Additionally, cross-sectional transmission electron microscopy (TEM) revealed that many threading dislocations formed in sample A by edge type dislocations and intermittently appeared due to inter-crack. (C) 2010 Elsevier B.V. All rights reserved.
Hydrogen etch of GaN and its application to produce porous GaN caves
(2011)
Yeh, Yen-Hsien
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Hsu, Ying-Chia
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Wu, Yin-Hao
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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
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Chen, Kuei-Ming
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Wu, Yin-Hao
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Hsu, Ying-Chia
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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
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Chen, Kuei-Ming
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Wu, Yin-Hao
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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.
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
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Wu, Yin-Hao
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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
Stress and Defect Distribution of Thick GaN Film Homoepitaxially Regrown on Free-Standing GaN by Hydride Vapor Phase Epitaxy
(2010)
Chen, Kuei-Ming
;
Yeh, Yen-Hsien
;
Wu, Yin-Hao
;
Chiang, Chen-Hao
;
Yang, Din-Ru
A 220-mu m-thick Gallium nitride (GaN) layer was homoepitaxially regrown on the Ga-polar face of a 200-mu m-thick free-standing c-plane GaN by hydride vapor-phase epitaxy (HVPE). The boundary of the biaxial stress distribution in the GaN substrate after regrowth was clearly distinguished. One half part, the regrown GaN, was found to be more compressive than the other half part, the free-standing GaN. Additionally, the densities of the screw and mixed dislocations reduced from 2.4 x 10(7) to 6 x 10(6) cm(-2) after regrowth. Furthermore, the yellow band emission almost disappeared, accompanied by a peak emission at approximately 380 nm related to the edge dislocation was under slightly improved in regrown GaN. We conclude that the reduction of the dislocation defects and Ga vacancies and/or O impurities are the two main reasons for the higher compressive stress in the regrown GaN than in the free-standing GaN, causing the curvature of the GaN substrate to be twice concave after regrowth. (C) 2010 The Japan Society of Applied Physics