Browsing by Author "Binh Tinh Tran"

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2H-Silicon Carbide Epitaxial Growth on c-Plane Sapphire Substrate Using an AlN Buffer Layer and Effects of Surface Pre-Treatments
(2015-05-01)
Luong, Tien-Tung
;
Binh Tinh Tran
;
Ho, Yen-Teng
;
Wei, Ting-Wei
;
Wu, Yue-Han
The effects of surface pre-treatments and the role of an AN buffer layer for 2H-SiC growth on c-plane sapphire substrates by thermal CVD are investigated. While the crystallinity of SiC directly grown on sapphire substrate always degrades with a hydrogen pre-treatment but improves by optimizing carbonization, the crystallinity of SiC grown on sapphire substrate using an AN buffer grown by MOCVD improves with sufficient time of exposure to the H pre-treatment but always deteriorates with carbonization. Detailed microstructural analysis by phi-scan x-ray diffraction reveals that SiC film grown on sapphire substrate consists of crystalline domains with two different crystallographic orientations which are rotated relative to each other along the [111] axis by 60 degrees. A highly oriented hexagonal 2H-SiC film is obtained on low-cost c-plane sapphire substrate by using an AN buffer. 2H-SiC is unambiguously determined not only by phi-scan x-ray diffraction but also by high-resolution transmission electron microscopy. The growth relationship between 2H-SiC and 2H-AlN are coherent due to the favorable bonding of C and Al between SiC and AlN.
Barrier Strain and Carbon Incorporation-Engineered Performance Improvements for AlGaN/GaN High Electron Mobility Transistors
(2015-03-01)
Tien Tung Luong
;
Ho, Yen Teng
;
Binh Tinh Tran
;
Woong, Yuen Yee
;
Chang, Edward Yi
The improvements in electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) grown using metal-organic (MO) CVD by engineering structure, barrier strain, and unintentional carbon incorporation, are demonstrated in this work. Both normal HEMT structure (with a high temperature (HT) AlN buffer) and advanced HEMT structure (with a high-low-high temperature (HLHT) AlN buffer, and a HT AlN interlayer (IL)) present a breakdown voltage higher than 200 V, while a much smaller breakdown voltage of 17V is measured on the conventional structure using a low-temperature GaN buffer. The HT AlN IL inserted in the middle of the conventional HEMT structure introduces a reduction in the tension of the AlGaN barrier, which results in an improvement of the surface morphology (0.46 nm). As a consequence, the two-dimensional electron gas (2DEG) mobility increases by remarkable 46% (1900 cm(2) V-1 s(-1)). The HLHT AlN buffer, substituting for the HT AlN buffer, leads to the enhancement of GaN crystalline quality, which contributes to the performance improvement for HEMTs. The advanced HEMT, using both an AlN IL and an HLHT AlN buffer, produces increases in the DC maximum drain current by 35.5% (similar to 680Amm(-1)), and in the transconductance by 15% (114 mSmm(-1)) in comparison with the normal HEMT with an AlN buffer. The very low leakage current in the advanced HEMTs is caused by optimizing the design of the buffer and modifying growth parameters. Lastly, the reduction of AlGaN barrier tensile strain by inserting the HT AlN IL is promising for an improvement in AlGaN/GaN HEMT reliability.
Broadband antireflection sub-wavelength structure of InGaP/InGaAs/Ge triple junction solar cell with composition-graded SiNx
(2015-05)
Chung, Chen-Chen
;
Lo, Hsiao-Chieh
;
Lin, Yen-Ku
;
Yu, Hung-Wei
;
Binh Tinh Tran
This work reports a fabrication strategy to improve the antireflective ability of a InGaP/GaAs/Ge triple-junction solar cell, by combining a nano-templating technique and a chemical-synthesis approach. SiH4 and N-2 were used as ammonia-free reaction gases in a plasma-enhanced chemical vapor deposition (PECVD) to prepare Si3N4 as an original antireflective coating (ARC) layer with better chemical stability. Composition-graded SiNx was successfully integrated with sub-wavelength structure by modulating SiH4/N-2 ratio during PECVD deposition, and followed by a controllable gold-nanoparticle masking technique on top of the solar cell. Finite-difference time-domain solution was employed to simulate and optimize the aspect-ratio of the ARC, under the condition of variable refractive index over a broad wavelength window, and followed by the masking technique to obtain the desired ARC dimension. This enabled a low light reflectance (<10%) over a broad spectral bandwidth (300-1800 nm) for the solar cell with excellent stability, because of the triple advantages of structural optimization, better chemical stability and graded refractive index of the ARC. The solar cell\'s performance was tested and showed great competitiveness to those of forefront studies, suggesting the feasibility of the proposed technology.
Effect of Multiple AlN Layers on Quality of GaN Films Grown on Si Substrates
(2014-11-01)
Binh Tinh Tran
;
Lin, Kung-Liang
;
Sahoo, Kartika Chandra
;
Chung, Chen-Chen
;
Chi-Lang Nguyen
In this paper, we present the effect of multiple thin high-low-high-temperature AlN (HLHT AlN) nucleation layers on GaN film quality. A 1.9-mu m-thick GaN film gown on Si (111) substrate shows that the multiple HLHT AlN nucleation layers have a significant effect on GaN film quality. This process also plays a very important role in the growth of GaN films on Si (111) substrates. A high quality GaN film with a uniformly faceted surface with very low dislocation densities is obtained at the optimized multiple HLHT AlN nucleation layers 50-nm thick at a temperature of 1010-800-1010 degrees C and a growth pressure of 50 Torr.
Effect of the Circle-Grid Electrodes on Concentrated GaAs Solar Cell Efficiency
(2014-09-01)
Chung, Chen-Chen
;
Binh Tinh Tran
;
Han, Ming-Hung
;
Lin, Kung-Liang
;
Yu, Hung-Wei
In this study, we investigate the effect of the shading factor of the front grid pattern on concentrated solar cell efficiency, taking the trade-off between the series resistance of the electrodes and the amount of incident light into consideration. We examine the thermal effect with regard to five different circle-grid electrode patterns of the front contact. The front contacts with different grid patterns affect the characteristics of light-concentrated-type GaAs single-junction solar cells. The device parameters analyzed include the open-circuit voltage (V-oc), short-circuit current (I-sc), fill factor (FF) and conversion efficiency (eta). The results of our study show that for a concentration ratio greater than 60x with AM1.5G, the device with a shading factor of 7.1% has the best cell efficiency of 27.05%, due to the smaller current crowding at the center spot. The results indicate that the conversion efficiency of solar cells can be improved by establishing a compromise between the shading effect and the series resistance effect.
Efficiency improvement of InGaP/GaAs/Ge solar cells by hydrothermal-deposited ZnO nanotube structure
(2014-07-05)
Chung, Chen-Chen
;
Binh Tinh Tran
;
Lin, Kung-Liang
;
Ho, Yen-Teng
;
Yu, Hung-Wei
In this paper, a zinc oxide (ZnO) nanotube, fabricated by the hydrothermal growth method on triple-junction (T-J) solar cell devices to enhance efficiency, is investigated. Compared to those of bare T-J solar cells (without antireflection (AR) coating) and solar cells with Si3N4 AR coatings, the experimental results show that the T-J solar cells, which use a ZnO nanotube as an AR coating, have the lowest reflectance in the short wavelength spectrum. The ZnO nanotube has the lowest light reflection among all experimental samples, especially in the range of 350 to 500 nm from ultraviolet (UV) to visible light. It was found that a ZnO nanotube can enhance the conversion efficiency by 4.9%, compared with a conventional T-J solar cell. The Si3N4 AR coatings also enhance the conversion efficiency by 3.2%.The results show that a cell with ZnO nanotube coating could greatly improve solar cell performances.
Growth of GaN films on circle array patterned Si (111) substrates
(2014-09-01)
Lin, Kung-Liang
;
Binh Tinh Tran
;
Chung, Chen-Chen
;
Chang, Edward-Yi
;
材料科學與工程學系
Low stress, low defect density GaN was successfully grown on circle array patterned Si (111) substrate using AlN as the buffer followed by two steps growth of the GaN film. Raman measurement shows a reduction of in plane biaxial stress for the GaN film grown on patterned substrate. The slight blueshifL of PL peaks further provides evidence that the tensile stress in the GaN film was relaxed, It is believed that the grain boundaries of the polycrystalline AlN buffer layer and the dislocations in the GaN film grown helped to relieve the stress induced by the lattice and the thermal coefficient mismatches during growth. (C) 2014 Elsevier By. All rights reserved.
Growth of lattice-matched InAlN/GaN on Si (111) substrate for ultraviolet photodiode application
(2013-09-01)
Binh Tinh Tran
;
Chang, Edward Yi
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In this paper, we report on the growth of high quality In (x) Al1-x N/GaN hetero-structures on Si substrate by metal organic chemical vapor deposition with various indium compositions (x = 10.2, 16.2 and 17.6%). The lattice-matched In0.176Al0.838N/GaN structure shows a smooth surface with good crystalline quality. In addition, the ultraviolet photodiode device shows excellent device characteristics with a low leakage current of 0.12 A mu A, and a high spectral response. It has good quantum efficiency of 94 mA/W and 44% at 265 nm which is comparable to that of the InAlN photodiode grown on sapphire substrate.
InGaP/GaAs Dual-Junction Solar Cell with AlGaAs/GaAs Tunnel Diode Grown on 10 degrees off Misoriented GaAs Substrate
(2012-08-01)
Yu, Hung Wei
;
Chung, Chen Chen
;
Wang, Chin Te
;
Hong Quan Nguyen
;
Binh Tinh Tran
InGaP/GaAs dual-junction solar cells with different tunnel diodes (TDs) grown on misoriented GaAs substrates are investigated. It is demonstrated that the solar cells with P++-AlGaAs/N++-GaAs TDs grown on 10 degrees off GaAs substrates not only show a higher external quantum efficiency (EQE) but also generate a higher peak current density (J(peak)) at higher concentration ratios (185 x) than the solar cells with P++-GaAs/N++-InGaP TDs grown on 6 degrees off GaAs substrates. Furthermore, the cell design with P++-AlGaAs/N++-GaAs TDs grown on 10 degrees off GaAs substrates does not generate a disordered InGaP epitaxial layer during material growth, and thus shows superior current-voltage characteristics. (c) 2012 The Japan Society of Applied Physics
Performance Improvements of AlGaN/GaN HEMTs by Strain Modification and Unintentional Carbon Incorporation
(2015-03-01)
Tien-Tung Luong
;
Binh Tinh Tran
;
Ho, Yen-Teng
;
Minh-Thien-Huu Ha
;
Hsiao, Yu-Lin
An advanced AlGaN/GaN HEMT structure, grown on a sapphire substrate by MOCVD utilizing a high temperature (HT) AN interlayer (IL) and a multilayer high-low-high temperature (HLH) AN buffer layer, demonstrates a superior performance both in breakdown voltage (>200 V) and maximum drain current (Ipss = 667 mA/mm). The HT AN IL produces an additional compressive strain into the above GaN layer. Accordingly, an AlGaN barrier, grown on the more compressive GaN, introduces less tensile strain leading to an improvement in surface morphology (RMS = 0.19 nm in 2 x 2 mu m(2)), a remarkable increase in 2DEG mobility by 46% (mu(S)= 1900 cm(2)/Vs) and a decrease in densities of defects acting as paths for the leakage current through the AlGaN barrier. A high semi-insulating buffer is achieved by eliminating leakage paths both through the buffer layer and the buffer-substrate interfacial layer. These result from an increase in unintentional carbon introduced by AIN layers, especially by a low temperature AN layer; which are grown under low pressure (50 Ton). Lastly, the decrease in AlGaN barrier tensile strain and low leakage current in the advanced HEMTs structure using an HT AN IL and an HLH AIN buffer are promising for an improvement in AlGaN/GaN HEMTs\' reliability.
The Growth and Fabrication of High-Performance In0.5Ga0.5As Metal-Oxide-Semiconductor Capacitor on GaAs Substrate by Metalorganic Chemical Vapor Deposition Method.
(2012-01-01)
Hong Quan Nguyen
;
Hai Dang Trinh
;
Yu, Hung Wei
;
Hsu, Ching Hsiang
;
Chung, Chen Chen
Growth conditions have investigated for growing high quality In0.3Ga0.7As and In0.5Ga0.5As on GaAs substrate by metalorganic chemical vapor deposition method. Annihilation reactions between threading dislocations observed by transmission electron microscopy are experimental evidences to confirm threading dislocations had been blocked in InxGa1-xAs buffer layers. A high quality smooth surface In0.5Ga0.5As epi-film with threading dislocation density of 2x10(6) cm(-2) was achieved at growth temperature of 490 degrees C. Metal-oxide-semiconductor capacitor devices fabricated on In0.5Ga0.5As/GaAs perform nice capacitance-voltage response, with small frequency dispersion. The conductance contours indicate that the Fermi level moves freely to the lower part of the InGaAs bandgap without pinning.