Browsing by Author "Wu, Yin-Hao"

Now showing 1 - 10 of 10

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
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.
Homoepitaxy on GaN substrate with various treatments by metalorganic vapor phase epitaxy
(2011-03-01)
Chen, Kuei-Ming
;
Wu, Yin-Hao
;
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
;
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.
Method for modulating the wafer bow of free-standing GaN substrates via inductively coupled plasma etching
(2010-12-01)
Chen, Kuei-Ming
;
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
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
The effect of free-standing GaN substrate on carrier localization in ultraviolet InGaN light-emitting diodes
(2014-12-13)
Tsai, Ming-Ta
;
Chu, Chung-Ming
;
Huang, Che-Hsuan
;
Wu, Yin-Hao
;
Chiu, Ching-Hsueh
In this study, we have grown 380-nm ultraviolet light-emitting diodes (UV-LEDs) based on InGaN/AlInGaN multiple quantum well (MQW) structures on free-standing GaN (FS-GaN) substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD), and investigated the relationship between carrier localization degree and FS-GaN. The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown. High-resolution X-ray diffraction (HRXRD) analyses demonstrated high-order satellite peaks and clear fringes between them for the UV-LEDs grown on the FS-GaN substrate, from which the interface roughness (IRN) was estimated. The temperature-dependent photoluminescence (PL) measurement confirmed that the UV-LEDs grown on the FS-GaN substrate exhibited better carrier confinement. Besides, the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) mapping images verified that the UV-LEDs on FS-GaN have fairly uniform distribution of indium and more ordered InGaN/AlInGaN MQW structure. Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current. Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.
Use of hydrogen etching to remove existing dislocations in GaN epitaxial layers
(2015-08-01)
Yeh, Yen-Hsien
;
Chu, Chung-Ming
;
Wu, Yin-Hao
;
Hsu, Ying-Chia
;
Yu, Tzu-Yi
In this paper, based on the anisotropic nature of hydrogen (H-2) etching on GaN, we describe a new approach to the removal of threading dislocations in GaN layers. The top surfaces of c-plane (Ga-face) and a-plane GaNs are considered stable in H-2; therefore, H-2 etches only crystal imperfections such as dislocation and basal plane stacking fault (BSF) sites. We used H-2 to etch undoped c-plane GaN, n-type c-plane GaN, a-plane GaN, and an InGaN/ GaN multiple quantum well structure. Several examinations were performed, indicating deep cavities on the c-plane GaN samples after H-2 etching; furthermore, gorge-like grooves were observed on the a-plane GaN samples. The deep cavities on the c-plane GaN were considered the etched dislocation sites, and the gorge-like grooves on the a-plane GaN were considered the etched BSF sites. Photoluminescence measurements were performed and the results indicated that the H-2-etched samples demonstrate superior optoelectronic properties, probably because of the elimination of dislocations.