Browsing by Author "Chi, Tung-Wei"

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A novel dilute antimony channel In0.2Ga0.8AsSb/GaAs HEMT
(2007-02-01)
Su, Ke-Hua
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Hsu, Wei-Chou
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Lee, Ching-Sung
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Wu, Tsung-Yeh
;
Wu, Yue-Han
This letter reports, for the first time, a high-electron mobility. transistor (HEMT) using A dilute antimony In0.2Ga0.8AsSb channel, which is grown by a molecular-beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the HEMT device was effectively improved by introducing the surfactantlike Sb atoms during the growth of the InGaAs layer. The improved heterostructural quality and electron transport properties have also been verified by various surface characterization techniques. In comparison, the proposed HEMT with (without) the incorporation of Sb atoms has demonstrated the maximum extrinsic transconductance g(m,max) of 227 (180) mS/mm, a drain saturation current density I-DSS of 218 (170) mA/mm, a gate-voltage swing of 1.215 (1.15) V, a cutoff frequency f(T) of 25 (20.6) GHz, and the maximum oscillation frequency f(max) of 28.3 (25.6) GHz at 300 K with gate dimensions of 1.2 x 200 mu m(2).
Analysis of InAsN quantum dots by transmission electron microscopy and photoluminescence
(2008-10-01)
Hsu, Chiung-Chih
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Hsu, Ray-Quen
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Wu, Yue-Han
;
Chi, Tung-Wei
;
Chiang, Chen-Hao
Quantum dots (QDs) have great potential in optical fiber communication applications were widely recognized. The structure of molecular beam epitaxy (MBE) grew InAsN QDs were investigated by transmission electron microscopy (TEM) and measured their optical properties by photoluminescence (PL). TEM images show that the InAsN QDs are irregular or oval shaped. Some of the InAsN QDs are observed to have defects, such as dislocations at or near the surface in contrast to InAs QDs, which appear to be defect free. PL results for InAsN QDs showed a red-shifted emission peak. In addition, the InAsN emission peak is broader than InAs QDs, which supports the TEM observation that the size distribution of the InAsN QDs is more random than InAs QDs. The results show that the addition of nitrogen to InAs QDs leads to a decrease in the average size of the QDs, bring changes in the QD's shape, compositional distribution, and optical properties. (C) 2008 Published by Elsevier B.V.
High-Quality Free-standing GaN Thick-films Prepared by Hydride Vapor Phase Epitaxy using Stress Reducing Techniques
(2009)
Huang, Hsin-Hsiung
;
Lee, Wei-I
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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.
Investigations on highly stable thermal characteristics of a dilute In(0.2)Ga(0.8)AsSb/GaAs doped-channel field-effect transistor
(2008-04-01)
Su, Ke-Hua
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Hsu, Wei-Chou
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Lee, Ching-Sung
;
Hu, Po-Jung
;
Wu, Yue-Han
This work reports for the first time a novel In(0.2)Ga(0.8)AsSb/GaAs heterostructure doped-channel field-effect transistor (DCFET) grown by the molecular beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the DCFET device has been effectively improved by introducing surfactant-like Sb atoms during the growth of the Si-doped InGaAs channel layer. The improved device characteristics include the peak extrinsic transconductance (g(m, max)) of 161.5 mS mm(-1), the peak drain-source saturation current density (IDSS, max) of 230 mA mm(-1), the gate-voltage swing (GVS) of 1.65 V, the cutoff frequency (f(T)) of 12.5 GHz and the maximum oscillation frequency (f(max)) of 25 GHz at 300 K with the gate dimensions of 1.2 x 200 mu m(2). The proposed design has also shown a stable thermal threshold coefficient (partial derivative V(th)/partial derivative T) of -0.7 mV K(-1).
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
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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
Strain-reduced GaN thick-film grown by hydride vapor phase epitaxy utilizing dot air-bridged structure
(2009-05-01)
Huang, Hsin-Hsiung
;
Chao, Chu-Li
;
Chi, Tung-Wei
;
Chang, Yu-Lin
;
Liu, Po-Chun
A 300 pm GaN thick-film, in diameter 1.5 in, was demonstrated without any crack by hydride vapor phase epitaxy (HVPE) growth. The technique used in relaxing the residual stress caused by differences of thermal expansion coefficients (TEC) and lattice constants between GaN and sapphire substrate to prevent GaN film from crack is called a dot air-bridged structure. After the laser lift-off process, 300-mu m-thick freestanding GaN wafer, in diameter 1.5 in, could be fabricated. The compressive stress in the dot air-bridged structure was measured by micro-Raman spectroscopy with the E(2)(high) phonon mode. The compressive stress could be reduced to as small as 0.04 GPa, which could prevent the crack during the epitaxial process for GaN growth by HVPE. It is important to obtain a large-area crack-free GaN thick-film, which can be used for fabricating freestanding GaN wafer. Crown Copyright (C) 2009 Published by 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
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Wu, Yin-Hao
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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
Triangular extended microtunnels in GaN prepared by selective crystallographic wet chemical etching
(2008)
Huang, Hsin-Hsiung
;
Wu, Pei-Lun
;
Zeng, Hung-Yu
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Liu, Po-Chun
;
Chi, Tung-Wei
Extended microtunnels with triangular cross sections in thick GaN films were demonstrated using wet chemical etching on specially designed epitaxial lateral overgrowth structures. For tunnels along the < 1 (1) over bar 00 > and < 11 (2) over bar0 > directions of GaN, the {11 (22) over bar} and {10 (11) over bar} facets are the etch stop planes with activation energies of 23 kcal/mol determined by wet chemical etching. The axial etching rate of the tunnels in the < 1 (1) over bar 00 > direction is twice as large than that along the < 11 (2) over bar0 > direction. The highest etching rate of the tunnels in the axial direction is 1000 mu m/h. (C) 2008 The Electrochemical Society.