Browsing by Author "Wang, Wei-Kai"

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1.48-kV enhancement-mode AlGaN/GaN high-electron-mobility transistors fabricated on 6-in. silicon by fluoride-based plasma treatment
(2016-05-01)
Yeh, Chih-Tung
;
Wang, Wei-Kai
;
Shen, Yi-Siang
;
Horng, Ray-Hua
;
電機學院
Enhancement-mode AlGaN/GaN high-electron-mobility transistors (HEMTs) were fabricated on a Si substrate by fluorine plasma treatment without pre-etching. The threshold voltage shifted from % 8 to 2.3 V, effectively converting the depletion-mode HEMT to the enhancement-mode HEMT. The leakage current was reduced by two orders of magnitude by CF4 plasma treatment. The device exhibited a superior performance with a maximum drain saturation current of 210mA/mm at V-GS = 10V and a peak gain of 44.1mS/mm. A low off-state gate leakage current of 10(-6)mA/mm, ION/IOFF ratio of approximately 10(8), and high breakdown voltage of 1480V were obtained. (C) 2016 The Japan Society of Applied Physics
1.48-kV enhancement-mode AlGaN/GaN high-electron-mobility transistors fabricated on 6-in. silicon by fluoride-based plasma treatment
(2016-05)
Yeh, Chih-Tung
;
Wang, Wei-Kai
;
Shen, Yi-Siang
;
Horng, Ray-Hua
;
電機學院
Enhancement-mode AlGaN/GaN high-electron-mobility transistors (HEMTs) were fabricated on a Si substrate by fluorine plasma treatment without pre-etching. The threshold voltage shifted from % 8 to 2.3 V, effectively converting the depletion-mode HEMT to the enhancement-mode HEMT. The leakage current was reduced by two orders of magnitude by CF4 plasma treatment. The device exhibited a superior performance with a maximum drain saturation current of 210mA/mm at V-GS = 10V and a peak gain of 44.1mS/mm. A low off-state gate leakage current of 10(-6)mA/mm, ION/IOFF ratio of approximately 10(8), and high breakdown voltage of 1480V were obtained. (C) 2016 The Japan Society of Applied Physics
Characterizations of Metal-Oxide-Semiconductor Field-Effect Transistors of ZnGaO Grown on Sapphire Substrate
(2017-03-01)
Shen, Yi-Siang
;
Wang, Wei-Kai
;
Horng, Ray-Hua
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Zinc gallate (ZnGaO) epilayers were grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition and fabricated into metal-oxide-semiconductor field-effect transistors (MOSFETs). The ZnGaO MOSFETs exhibited a complete channel pinch-off of the drain current for VGS < -4.43 V, high off-state breakdown voltage of 378 V, high I-ON/I-OFF ratio of 10(6), and low gate leakage current.
Improvement of light extraction for AlGaN-based near UV LEDs with flip-chip bonding fabricated on grooved sapphire substrate using laser ablation
(2019-06-01)
Ku, Chun-Han
;
Wang, Wei-Kai
;
Horng, Ray-Hua
;
交大名義發表
;
電子工程學系及電子研究所
Mesh-textured flip-chip (FC) structures of AlGaN-based near ultraviolet-light-emitting diodes (NUV-LEDs) are fabricated using an Nd:YAG laser scriber. Compared with the output power of the reference FC-LEDs, those of conventional sapphire substrate (CSS) FC-LEDs and the patterned sapphire substrate FC-LEDs with laser-scribed mesh-textured backsides were improved by 28.7% and 7.2%, respectively. The CSS FC-LED is enhanced using the mesh-textured trench pattern attributable to an increase in the light-extraction efficiency resulting from an increase in the photon-escape probability due to enhanced light scattering at the trench-patterned-sapphire/air interface. Furthermore, the current-voltage curves depict that the laser scribing process does not adversely affect the electrical properties of the FC-LEDs. A Trace-Pro simulation revealed that the laser-scribed-trench CSS FC-LED is effective for light extraction.
Reduction of Defects in AlGaN Grown on Nanoscale-Patterned Sapphire Substrates by Hydride Vapor Phase Epitaxy
(2017-06-01)
Tasi, Chi-Tsung
;
Wang, Wei-Kai
;
Tsai, Tsung-Yen
;
Huang, Shih-Yung
;
Horng, Ray-Hua
In this study, a 3-m-thick AlGaN film with an Al mole fraction of 10% was grown on a nanoscale-patterned sapphire substrate (NPSS) using hydride vapor phase epitaxy (HVPE). The growth mechanism, crystallization, and surface morphology of the epilayers were examined using X-ray diffraction, transmission electron microscopy (TEM), and scanning electron microscopy at various times in the growth process. The screw threading dislocation (TD) density of AlGaN-on-NPSS can improve to 1-2 x 10(9) cm(-2), which is significantly lower than that of the sample grown on a conventional planar sapphire substrate (7 x 10(9) cm(-2)). TEM analysis indicated that these TDs do not subsequently propagate to the surface of the overgrown AlGaN layer, but bend or change directions in the region above the voids within the side faces of the patterned substrates, possibly because of the internal stress-relaxed morphologies of the AlGaN film. Hence, the laterally overgrown AlGaN films were obtained by HVPE, which can serve as a template for the growth of ultraviolet III-nitride optoelectronic devices.
Structural and Stress Properties of A1GaN Epilayers Grown on A1N-Nanopatterned Sapphire Templates by Hydride Vapor Phase Epitaxy
(2018-09-01)
Tasi, Chi-Tsung
;
Wang, Wei-Kai
;
Ou, Sin-Liang
;
Huang, Shih-Yung
;
Horng, Ray-Hua
In this paper, we report the epitaxial growth and material characteristics of AlGaN (Al mole fraction of 10%) on an AlN/nanopatterned sapphire substrate (NPSS) template by hydride vapor phase epitaxy (HYPE). The crystalline quality, surface morphology, microstructure, and stress state of the AlGaN/AlN/NPSS epilayers were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The results indicate that the crystal quality of the A1GaN film could be improved when grown on the A1N/NPSS template. The screw threading dislocation (TD) density was reduced to 1.4 x 10(9) cm(-2) for the AlGaN epilayer grown on the A1N/NPSS template, which was lower than that of the sample grown on a flat c-plane sapphire substrate (6.3 x 10(9) cm(-2)). As examined by XRD measurements, the biaxial tensile stress of the AlGaN film was significantly reduced from 1,187 MPa (on A1N/NPSS) to 38.41 MPa (on flat c-plane sapphire). In particular, an increase of the Al content in the overgrown AlGaN layer was confirmed by the TEM observation. This could be due to the relaxation of the in-plane stress through the AlGaN and AlN/NPSS template interface.
Transparent electrode design for AlGaN deep-ultraviolet light-emitting diodes
(2017-12-11)
Hrong, Ray-Hua
;
Zeng, Yu-Yuan
;
Wang, Wei-Kai
;
Tsai, Chia-Lung
;
Fu, Yi-Keng
Zinc gallate (ZnGa2O4; ZGO) thin films were employed as the p-type transparent contact layer in deep-ultraviolet AlGaN-based light-emitting diodes (LEDs) to increase light output power. The transmittance of 200-nm-thick ZGO in deep-ultraviolet wavelength (280 nm) was as high as 92.3%. Two different ohmic contact structures, a dot-LED (D-LED; ZGO/dot-ITO/LED) and whole-LED (W-LED; ZGO/ITO/LED), exhibited improved light output power and current spreading compared to a conventional ITO-LED (C-LED). At an injection current of 20 mA, the D-LED and W-LED exhibited 33.7% and 12.3% enhancements in light output power, respectively, compared to the C-LED. The enhanced light output power of the D-LED can be attributed to an improvement in current spreading and enhanced light-extracting efficiency achieved by introducing ZGO/dot-ITO. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement