Browsing by Author "Dee, Chang-Fu"

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A rapid responding ultraviolet sensor based on multi-parallel aligned ZnO nanowires field effect transistor
(2017-06-15)
Tiong, Teck-Yaw
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Dee, Chang-Fu
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Hamzah, Azrul Azlan
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Goh, Boon Tong
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Wong, Yuan-Yee
One-dimensional zinc oxide nanowires (ZnO NWs) have been reported to be suitable for UV sensing, but their applications are limited due to restricted surface area which restrains the performance especially in term of response and recovery. In this paper, we fabricate a UV sensor using multi-parallel aligned ZnO NWs based FET in order to overcome the mentioned drawbacks. The sensing characteristics of multi parallel aligned ZnO NWs based FET toward 0.44 mW/cm(2) UV illumination has been examined under depletion and enhancement modes, at ambient conditions. The fabricated UV sensor was found to possess the ability to differentiate UV with different intensity, improved sensitivity (in depletion mode), short response and recovery time (< 1 s), and with high stability. Our paper reports a simple and effective approach for UV sensor fabrication with high responsivity, sensitivity and reproducibility. (C) 2017 Elsevier B.V. All rights reserved.
Analysis of Leakage Current Mechanism for Ni/Au Schottky Contact on InAlGaN/GaN HEMT
(2018-06-06)
Lumbantoruan, Franky
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Wu, Chia-Hsun
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Zheng, Xia-Xi
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Singh, Sankalp K.
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Dee, Chang-Fu
The gate leakage mechanism for InAlGaN/GaN high electron mobility transistors (HEMTs) is systematically studied using temperature-dependent gate current-voltage characteristics. The electric field across the barrier layer is calculated through the extracted polarization charge and dielectric constant of the InAlGaN/GaN HEMT. The gate current of the InAlGaN/GaN HEMT is analyzed by fitting the experimental data using Themionic Emission (TE), Poole-Frenkel (PF), and Fowler-Nordheim (FN) tunneling. The results show that 1) reverse leakage current in the thin InAlGaN barrier layer is dominated by FN tunneling due to triangular barrier formation; 2) for thicker barrier layer, the reverse leakage current at low electric field (<2.23MVcm(-1)) is dominated by PF emission; 3) at high electric field near the threshold voltage the FN tunneling dominates. Extraction of effective barrier height by fitting the experimental data with models leads to the suggestion for the improvement of the device leakage current.
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
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Lin, Yueh-Chin
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Chu, Chung-Ming
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Chuang, Yu-Lin
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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.
Crystal structure control of Au-free InAs and InAs/GaSb heterostucture nanowires grown on Si (111) by metal-organic chemical vapor deposition
(2019-01-01)
Kakkerla, Ramesh Kumar
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Anandan, Deepak
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Singh, Sankalp Kumar
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Yu, Hung Wei
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Lee, Ching-Ting
In this letter, the growth of gold-free GaSb on various InAs nanowire (NW) crystal structures using metal-organic chemical vapor deposition is demonstrated. The GaSb was grown radially and axially on wurtzite (WZ), zinc-blend (ZB) and polytype (mixture of WZ and ZB) InAs NWs. The effect of the various InAs crystal structures on GaSb was studied. This study demonstrates the control of the crystal growth of InAs and InAs/GaSb heterostructure NWs through the optimization of growth parameters and crystal transfer from core to shell, such techniques are necessary for the growth of NWs for future nanoelectronic device applications, such as TFET. (C) 2018 The Japan Society of Applied Physics
Effective Passivation With High-Density Positive Fixed Charges for GaN MIS-HEMTs
(2017-05-01)
Liu, Shih-Chien
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Huang, Chung-Kai
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Chang, Chia-Hua
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Lin, Yueh-Chin
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Chen, Bo-Yuan
An effective passivation with high-density positive fixed charges was demonstrated on GaN MIS-HEMTs. The positive fixed charges at the interface between passivation and AlGaN surface can reduce the surface potential and expand the quantum well under Fermi level. Besides, to satisfy charge balance, the net charge density at the AlGaN surface must equal to the 2DEG carrier density. Thus, the positive fixed charges passivation can increase the 2DEG carrier density and improve the switching performance of GaN MIS-HEMTs. In this paper, we demonstrated a high-density positive fixed charges (similar to 2.71 x 10(13) e/cm(-2)) passivation using SiON for GaN MIS-HEMTs. The device with SiON passivation exhibits significant improvements in I-V characteristics and dynamic R-ON compared to the conventional SiN passivated device.
Effective surface treatment for GaN metal-insulator-semiconductor high-electron-mobility transistors using HF plus N-2 plasma prior to SiN passivation
(2016-01-01)
Liu, Shih-Chien
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Trinh, Hai-Dang
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Dai, Gu-Ming
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Huang, Chung-Kai
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Dee, Chang-Fu
An effective surface cleaning technique is demonstrated for the GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) passivation process. In this study, dilute HF solution and in situ N-2 plasma treatments were adopted to remove the native oxide and recover the nitrogen-vacancy defects at the GaN surface before device passivation. To investigate the correlation between the properties of the SiN/GaN interface and the device performance, the GaN MIS-HEMTs were characterized using current-voltage (I-V) measurement, capacitance-voltage (C-V) measurement, and X-ray photoelectron spectroscopy (XPS) analysis. With the application of this surface treatment technique, the device exhibits improved I-V characteristics with low leakage current, low dynamic ON-resistance, and good C-V response with a steep slope. Overall, the results reveal that the oxide-related bonds and nitrogen-vacancy defects at the SiN/GaN interface are the root cause of the GaN MIS-HEMTs performance degradation. (C) 2016 The Japan Society of Applied Physics
Effective surface treatment for GaN metal-insulator-semiconductor high-electron-mobility transistors using HF plus N-2 plasma prior to SiN passivation
(2016-01)
Liu, Shih-Chien
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Trinh, Hai-Dang
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Dai, Gu-Ming
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Huang, Chung-Kai
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Dee, Chang-Fu
An effective surface cleaning technique is demonstrated for the GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) passivation process. In this study, dilute HF solution and in situ N-2 plasma treatments were adopted to remove the native oxide and recover the nitrogen-vacancy defects at the GaN surface before device passivation. To investigate the correlation between the properties of the SiN/GaN interface and the device performance, the GaN MIS-HEMTs were characterized using current-voltage (I-V) measurement, capacitance-voltage (C-V) measurement, and X-ray photoelectron spectroscopy (XPS) analysis. With the application of this surface treatment technique, the device exhibits improved I-V characteristics with low leakage current, low dynamic ON-resistance, and good C-V response with a steep slope. Overall, the results reveal that the oxide-related bonds and nitrogen-vacancy defects at the SiN/GaN interface are the root cause of the GaN MIS-HEMTs performance degradation. (C) 2016 The Japan Society of Applied Physics
Formation of a Multi-Arm Branched Nanorod of ZnO on the Si Surface via a Nanoseed-Induced Polytypic Crystal Growth Using the Hydrothermal Method
(2013-07-01)
Tan, Sin Tee
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Umar, Akrajas Ali
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Yahaya, Muhammad
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Salleh, Muhamad Mat
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Yap, Chi Chin
A branched nanorod of ZnO composed of multiple branches that projects from a single nanorod backbone can be realized by using a hydrothermal approach in the presence of a nanoseed with a special structure, namely multi-faceted orthorhombic Zn2SiO4. Orthorhombic Zn2SiO4 was prepared by annealing the ZnO nanoseed of size ca. 15 nnn on a Si substrate at a temperature of 900 degrees C in air for one hour. A typical branched nanorod was constructed by a hexagonal-and rectangular-shaped nanorod arm. HRTEM analysis on the branched structure indicated that the branches exhibited a different crystal growth direction [002] and [100], reflecting the presence of a polytypic growth process in the formation of the branched nanorod structure. The branched nanorod of ZnO and its feature-rich faceted property appears promising for solar cell, catalytic and sensing applications.
Hydrothermal growth of ZnO nanotubes on InGaP/GaAs/Ge Solar Cells
(2014-01-01)
Chung, Chen-Chen
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Lin, Kung-Liang
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Yu, Hung-Wei
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Quan, Nguyen-Hong
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Dee, Chang-Fu
A new design where ZnO nanotubes were grown on the antireflection (AR) layer coated on triple-junction (T-J) solar cell devices to enhance the light conversion efficiency. Compared to the bare T-J solar cells (without an AR layer), the performance of Si3N4 AR coated solar cell showed improvement. The sample with a layer of ZnO nanotubes grown in top of AR layer showed the lowest light reflection compared with the bare and solely AR coated T-J solar cell especially in the spectrum range of 350-500 nm. The use of ZnO nanotubes have increased the conversion efficiency by 4.9% compared with the conventional T-J solar cell. While the Si3N4 AR coated sample only increased the conversion efficiency by 3.2%. This result is quite encouraging as further refinement and variation in the experiment procedures could possibly bring more exciting performance in the future.
Influence of post deposition annealing temperatures on electrical properties of Al2O3/InSb MOSCAPs
(2012-01-01)
Hai-Dang Trinh
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Lin, Yue-Chin
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Chang, Edward Yi
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Hong-Quan Nguyen
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Wang, Shin-Yuan
The influence of post deposition annealing (PDA) temperatures on electrical characteristics of Al2O3/InSb metal-oxide-semiconductor capacitor (MOSCAP) structures is investigated. Low frequency C-V responses with strong inversion behavior in the whole range of measured frequency (100 Hz-1 MHz) are observed, indicating very short minority carrier response time in InSb. The PDA temperature of 300 degrees C and above would result in the reduction of maximum capacitance. At the PDA temperature of above 300 degrees C the C-V hysteresis, frequency dispersion and stretch out increases significantly, indicating the degradation of the MOSCAP structures. The degradation might relate to the interdiffusion between Al2O3 and InSb during thermal steps.
Low resistance copper-based ohmic contact for AlGaN/GaN high electron mobility transistors
(2013-10-07)
Wong, Yuen-Yee
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Chen, Yu-Kong
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Maa, Jer-Shen
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Yu, Hung-Wei
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Tu, Yung-Yi
Ti/Al/Ni/Cu ohmic contact for AlGaN/GaN structure has been fabricated. The Ni layer played an important role in achieving low specific contact resistance (r(c)), smooth morphology, and excellent edge acuity. With a 50-angstrom Ni layer, a r(c) of 1.35 x 10(-6) Omega-cm(2) and a root-mean-square roughness of 7.65 nm have been realized. The characterization results indicated that no evidence of Cu diffusion into the semiconductor layers. The formation of Al-Cu and Ti-Cu alloys might have confined the Cu within the ohmic metal. In the absence of gold, the surface roughening caused by Au-Al alloy in conventional Ti/Al/Ni/Au structure was also prevented. (C) 2013 AIP Publishing LLC.
Normally-Off Tri-Gate GaN MIS-HEMTs with 0.76 m Omega center dot cm(2) Specific On-Resistance for Power Device Applications
(2019-08-01)
Wu, Chia-Hsun
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Chen, Jian-You
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Han, Ping-Cheng
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Lee, Ming-Wen
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Yang, Kun-Sheng
A GaN metal-insulator-semiconductor high electronmobility transistor (MIS-HEMT) using tri-gate architecture and hybrid ferroelectric charge trap gate stack is demonstrated for normally-off operation. Compared with the conventional planar device, the tri-gate device has the 2-D electron gas (2-DEG) channel exposed on the nanowire sidewalls, so that the trapped charges in the HfON charge-trapping layer can easily deplete the channel from the sidewalls, leading to a high positive threshold voltage (V-th) to realize the normally-off operation. Moreover, through this electrostatic control on the sidewall, a high density of negative charge caused by hybrid ferroelectric charge trap gate stack with the optimized tri-gate structure, the tri-gate device can achieve normally-off GaN device with both low on-resistance (R-ON) and high positive V-th. The designed tri-gate device exhibits a high V-th of +2.61 V at current density (I-DS) = 1 mu A/mm, a high maximum current density (I-DS, MAX) of 896 mA/mm, a low R-ON of 5.0 Omega center dot mm and a high breakdown voltage (BV) of 788 V. To the best of our knowledge, the proposed tri-gate device shows the lowest specific on-resistance (R-ON,R- SP) among reported normallyoff GaN device results with BV > 650 V.
Threading Dislocation Blocking in Metamorphic InGaAs/GaAs for Growing High-Quality In0.5Ga0.5As and In0.3Ga0.7As on GaAs Substrate by Using Metal Organic Chemical Vapor Deposition
(2012-05-01)
Hong-Quan Nguyen
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Chang, Edward Yi
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Yu, Hung-Wei
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Hai-Dang Trinh
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Dee, Chang-Fu
High quality In0.3Ga0.7As and In0.51Ga0.49As epilayers have been successfully grown on the GaAs substrate by MOCVD. A cross-sectional study by transmission electron microscopy showed that the threading dislocations (TDs) have been successfully contained and limited within the buffer layers designed to stop the elongation of TDs into the In0.3Ga0.7As and In0.51Ga0.49As epilayers. A TD density of 1 x 10(6) cm(-2) in a fully relaxed In0.51Ga0.49As epilayer was achieved. The measurement of lifetimes of n- and p-type In0.51Ga0.49As has been done by using time-resolved photoluminescence. A great reduction in the number of recombination centers in the InGaAs epilayer has been shown. (c) 2012 The Japan Society of Applied Physics