Browsing by Author "Chu, Chung-Ming"

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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.
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.
Reliability study of high-k La2O3/HfO2 and HfO2/La2O3 stacking layers on n-In0.53Ga0.47As metal-oxide-semiconductor capacitor
(2016-02)
Chu, Chung-Ming
;
Lin, Yueh-Chin
;
Lee, Wei-I
;
Dee, Chang Fu
;
Wong, Yuen-Yee
This study investigates the time-dependent dielectric breakdown (TDDB) characteristics of La2O3/HfO2 and HfO2/La2O3 stacking layers on an n-In0.53Ga0.47As metal-oxide-semiconductor capacitor. Both designs improved the reliability compared with a single layer of HfO2. The TDDB followed the thermochemical E model. The current transportation mechanism changed from thermionic emission to Frenkel-Poole emission because of the traps creation under voltage stress. Both designs resulted in similar lifespans and voltage accelerating factors. However, the La2O3/HfO2 design had a longer lifespan because of the lower interface trap density and insertion of the HfO2 diffusion barrier layer between La2O3 and n-In0.53Ga0.47As. The oxide stacks exhibited excellent reliability and achieved a lifespan of 28.4 years. (C) 2016 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.
The Effect of the Thickness of the Low Temperature AlN Nucleation Layer on the Material Properties of GaN Grown on a Double-Step AlN Buffer Layer by the MOCVD Method
(2016-02)
Huang, Wei-Ching
;
Chu, Chung-Ming
;
Hsieh, Chi-Feng
;
Wong, Yuen-Yee
;
Chen, Kai-Wei
The influence of low-temperature AlN (LT-AlN) nucleation layer thickness on the material properties of the GaN layer grown on the double-step AlN layer is investigated. When GaN was grown without the LT-AlN nucleation layer, the GaN layer has low sheet resistance of 464 ohm/sq and the surface was decorated with pitted region. On the other hand, when a LT-AlN layer with a thickness of 5 nm was inserted, a GaN layer with sheet resistance higher than 10(6) ohm/sq was achieved. This thin nucleation layer also improved the GaN morphology, suppressed inversion domain formation, and reduced oxygen impurity incorporation. However, the surface morphology and quality of the GaN crystal were severely degraded when the LT-AlN thickness was increased to 10 nm due to the formation of disorientated grains in the LT-AlN layer.
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.