Browsing by Author "Huang, Wei-Ching"

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A Cu-based alloyed ohmic contact system on n-type GaAs
(2007-12-03)
Chen, Ke-Shian
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Chang, Edward Yi
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Lin, Chia-Ching
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Lee, Cheng-Shih
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Huang, Wei-Ching
An alloyed Pd/Ge/Cu Ohmic contact to n-type GaAs is reported for the first time. The Pd/Ge/Cu Ohmic contact exhibited a very low specific contact resistance of 5.73x10(-7) Omega cm(2) at a low annealing temperature of 250 degrees C. This result is comparable to the reported Pd/Ge and Au/Ge/Ni Ohmic contact systems to n-type GaAs with doping concentrations about 1x10(18) cm(-3). The Ohmic contact formation mechanisms and microstructure evolution were investigated using secondary ion mass spectrometry, x-ray diffraction, transmission electron microscopy, and energy dispersive spectrometer. The Ohmic contact behavior was related to the formation of Cu(3)Ge and PdGa(x)As(y) compounds after annealing. (c) 2007 American Institute of Physics.
Characterization of AlInN Layer Grown on GaN/Sapphire Substrate by MOCVD
(2013-02-01)
Huang, Wei-Ching
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Chang, Edward-Yi
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Wong, Yuen-Yee
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Lin, Kung-Liang
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Hsiao, Yu-Lin
The AlInN layers have been grown with different growth parameters on GaN/sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The effects of growth parameters such as pressure and temperature on the Al incorporation during AlInN material growth have been investigated. The results showed that lower pressure provides a tendency for higher Al incorporating in the AlInN layer. Besides, as the temperature was increased from 700 degrees C to 780 degrees C, an estimation of 4% reduction on the indium composition has been observed for each 20 degrees C increment. XRD analysis showed that the best crystal quality of AlInN occured at 80% Al composition because of the higher lattice matching with GaN. Based on the above criteria, an Al0.8In0.2N/GaN HEMT device with 2 mu m gate length has also been fabricated. The DC characteristics showed a saturated current, I-dss of 280 mA/mm and transconductance of 140 mS/mm.
Effect of Graded AlxGa1-xN Interlayer Buffer on the Strain of GaN Grown on Si (111) Using MOCVD Method
(2008)
Lin, KungLiang
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Chang, Edward-Yi
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Li, Tingkai
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Huang, Wei-Ching
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Hsiao, Yu-Lin
GaN film grown on Si substrate with AlN/AlxGa1-xN buffer is studied by low pressure metal organic chemical vapor deposition (MOCVD) method. The AlxGa1-xN film with Al composition varying from 0 similar to 0.66 was used. The correlation of the Al composition in the AlxGa1-xN film with the stress of the GaN film grown was studied using high resolution X-ray diffraction including symmetrical and asymmetrical omega/2 theta scans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1-xN buffer layer, crack-free GaN films can be successfully grown on Si (111) substrates using AlN and AlxGa1-xN buffer layers.
Effect of Graded AlxGa1-xN Layers on the Properties of GaN Grown on Patterned Si Substrates
(2012-02-01)
Hsiao, Yu-Lin
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Lu, Lung-Chi
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Wu, Chia-Hsun
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Chang, Edward Yi
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Kuo, Chien-I
2.2-mu m-thick crack-free GaN films were grown on patterned Si substrates. The crack-free GaN films were obtained by patterning Si substrate and optimizing the graded AlxGa1-xN layers. With the increase of the graded AlxGa1-xN layer thickness, the GaN crystal quality improved as judged from the X-ray diffraction data. By applying multi-AlxGa1-xN layers on the patterned Si substrate, a 31% reduction of tensile stress for the GaN film was obtained as measured by micro-Raman. For the AlGaN/GaN high electron mobility transistor grown on 1 x 1 cm(2) larger patterns, the device exhibits maximum drain current density of 776 mA/mm and maximum transconductance of 101 mS/mm. (c) 2012 The Japan Society of Applied Physics
Effect of Nitridation on the Regrowth Interface of AlGaN/GaN Structures Grown by Molecular Beam Epitaxy on GaN Templates
(2012-08-01)
Wong, Yuen-Yee
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Huang, Wei-Ching
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Trinh, Hai-Dang
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Yang, Tsung-Hsi
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Chang, Jet-Rung
AlGaN/GaN structures were regrown on GaN templates using plasma- assisted molecular beam epitaxy (PA-MBE). Prior to the regrowth, nitridation was performed using nitrogen plasma in the MBE chamber for different durations (0 min to 30 min). Direct-current measurements on high-electron-mobility transistor devices showed that good pinch-off characteristics and good interdevice isolation were achieved for samples prepared with a 30-min nitridation process. Current-voltage measurements on Schottky barrier diodes also revealed that, for samples prepared without nitridation, the reverse-bias gate leakage current was approximately two orders of magnitudes larger than that of samples prepared with a 30-min nitridation process. The improvement in the electrical properties is a result of contaminant removal at the regrowth interface which may be induced by the etching effect of nitridation.
Effects of Al(x)Ga(1-x)N interlayer for GaN epilayer grown on Si substrate by metal-organic chemical-vapor deposition
(2010-05-01)
Lin, Kung-Liang
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Chang, Edward-Yi
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Hsiao, Yu-Lin
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Huang, Wei-Ching
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Luong, Tien-Tung
GaN film grown on Si substrate using multilayer AlN/Al(x)Ga(1-x)N buffer is studied by the low-pressure metal-organic chemical-vapor deposition method. The Al(x)Ga(1-x)N films with Al composition varying from 1 to 0.66 were used to accommodate the stress induced between GaN and the Si substrate during GaN growth. The correlation of the Al composition in the Al(x)Ga(1-x)N films with respect to the stress induced in the GaN film grown was studied using high-resolution x-ray diffraction, including symmetrical and asymmetrical omega/2 theta scans and reciprocal space maps. It is found that with proper design of the Al composition in the Al(x)Ga(1-x)N buffer layer, crack-free GaN film can be successfully grown on 6 in. Si (111) substrates using multilayer AlN and Al(x)Ga(1-x)N buffer layers. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3385672]
Effects of initial GaN growth mode on the material and electrical properties of AlGaN/GaN high-electron-mobility transistors
(2014-09-01)
Wong, Yuen-Yee
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Chang, Edward Yi
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Huang, Wei-Ching
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Lin, Yueh-Chin
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Tu, Yung-Yi
AlGaN/GaN high-electron-mobility transistors (HEMTs) with different initial GaN growth modes were prepared on AIN/sapphire substrates. Secondary ion mass spectroscopy and Hall effect measurements confirmed that a highly conductive n-type region was generated at the GaN/AIN buffer interface during the three-dimensional to two-dimensional (3D-2D) growth mode transition. This n-type region was created by oxygen impurity incorporation during the 3D-2D growth mode transition, and its thickness increased with the transition time. The existence of this n-type conduction path not only changed the material properties but also degraded the device performance of HEMTs. (C) 2014 The Japan Society of Applied Physics
Effects of NH3 Flow Rate During AlGaN Barrier Layer Growth on the Material Properties of AlGaN/GaN HEMT Heterostructure
(2017-10-01)
Lumbantoruan, Franky J.
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Wong, Yuen-Yee
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Huang, Wei-Ching
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Yu, Hung-Wei
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Chang, Edward-Yi
NH3 flow rate during AlGaN barrier layer growth not only affects the growth efficiency and surface morphology as a result of parasitic reactions but also influences the concentration of carbon impurity in the AlGaN barrier. Carbon, which decomposes from metal precursors, plays a role in electron compensation for AlGaN/GaN HEMT. No 2-dimensional electron gas (2-DEG) was detected in the AlGaN/GaN structure if grown with 0.5 slm of NH3 due to the presence of higher carbon impurity (2.6 x 10(19) cm(-2)). When the NH3 flow rate increased to 6.0 slm, the carbon impurity reduced to 2.10 x 10(18) atom cm(-3) and the 2 DEG electron density recovered to 9.57 x 10(12) cm(-2).
Efficient inverted quasi-bilayer organic solar cells fabricated by using non-halogenated solvent processes
(2014-09-07)
Chang, Jung-Hao
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Wang, Hsiao-Fang
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Lin, Wei-Chieh
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Chiang, Kai-Ming
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Chen, Kuan-Chen
Here we demonstrate the fabrication of novel, "quasi-bilayer" inverted organic photovoltaic devices using halogen-free solvents. The inferior solubility of pristine fullerene in non-halogenated solvents was used to control the interpenetration of upper polymeric donor layers with bottom fullerene layers. Notably, island-like nano-morphologies were revealed by AFM, SEM, TEM, cross-sectional TEM images and PL quenching measurement. Correlation between device performance, thin-film nano-morphology and ac impedance was observed. High efficiencies of 6.55% and 7.15% were observed for PBDTTT-C-T and PTB7 cells, respectively. These results demonstrate that this novel process not only offers an effective new method to control the morphology of solar active layers but, more importantly, could also be applied to a wide range of current material systems to produce efficient devices that comply with the non-toxic halogen-free requirement.
Efficient inverted quasi-bilayer organic solar cells fabricated by using non-halogenated solvent processes
(2014-09-07)
Chang, Jung-Hao
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Wang, Hsiao-Fang
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Lin, Wei-Chieh
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Chiang, Kai-Ming
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Chen, Kuan-Chen
Here we demonstrate the fabrication of novel, "quasi-bilayer" inverted organic photovoltaic devices using halogen-free solvents. The inferior solubility of pristine fullerene in non-halogenated solvents was used to control the interpenetration of upper polymeric donor layers with bottom fullerene layers. Notably, island-like nano-morphologies were revealed by AFM, SEM, TEM, cross-sectional TEM images and PL quenching measurement. Correlation between device performance, thin-film nano-morphology and ac impedance was observed. High efficiencies of 6.55% and 7.15% were observed for PBDTTT-C-T and PTB7 cells, respectively. These results demonstrate that this novel process not only offers an effective new method to control the morphology of solar active layers but, more importantly, could also be applied to a wide range of current material systems to produce efficient devices that comply with the non-toxic halogen-free requirement.
Growth of GaN film on 150 mm Si (111) using multilayer AlN/AlGaN buffer by metal-organic vapor phase epitaxy method
(2007-11-26)
Lin, Kung-Liang
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Chang, Edward-Yi
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Hsiao, Yu-Lin
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Huang, Wei-Ching
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Li, Tingkai
High quality GaN film was successfully grown on 150 mm Si (111) substrate by metal-organic vapor phase epitaxy method using AlN multilayer combined with graded AlGaN layer as buffer. The buffer layer structure, film quality, and film thickness are critical for the growth of the crack-free GaN film on Si (111) substrate. Using multilayer AlN films grown at different temperatures combined with graded Al(1-x)Ga(x)N film as the buffer, the tensile stress on the buffer layer was reduced and the compressive stress on the GaN film was increased. As a result, high quality 0.5 mu m crack-free GaN epitaxial layer was successfully grown on 6 in. Si substrate. (C) 2007 American Institute of Physics.
Highly efficient organic solar cells using a solution-processed active layer with a small molecule donor and pristine fullerene
(2014)
Lin, Hao-Wu
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Chang, Jung-Hao
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Huang, Wei-Ching
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Lin, Yu-Ting
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Lin, Li-Yen
A new strategy has been successfully established to realize high efficiency small molecule organic solar cells with a solution-processed active layer composed of a small organic molecule as the donor and pristine C-70 as the acceptor. Using 1,2-dichlorobenzene as solvent, a homogeneous donor/C-70 blend active layer can be effectively formed either by spin- or bar-coating techniques. This method delivers organic solar cells with high power conversion efficiencies up to 5.9%.
InAs-Channel Metal-Oxide-Semiconductor HEMTs with Atomic-Layer-Deposited Al2O3 Gate Dielectric
(2009-01-01)
Chang, Chia-Yuan
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Chang, Edward Yi
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Huang, Wei-Ching
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Su, Yung-Hsuan
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Trinh, Hai-Dang
The performance of n-type metal-oxide-semiconductor HEMTs with an InAs-channel using atomic-layer-deposited Al2O3 as gate dielectric has been fabricated and evaluated. The device performances of a set of scaled transistors with different gate dielectric thicknesses of 3, 5 and 7 nm have been investigated to determine whether the architecture of Al2O3 dielectric on InAs-channel HEMT can demonstrate good properties at low bias conditions for high-speed, high performance CMOS applications. The results indicate that the high-performance InAs-channel MOS-HEMTs with an ALD Al2O3 gate dielectric are promising candidates for advanced post-Si CMOS applications.
Influence of AlN buffer layer thickness on material and electrical properties of InAlN/GaN high-electron-mobility transistors
(2015-07-01)
Huang, Wei-Ching
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Liu, Kuan-Shin
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Wong, Yuen-Yee
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Hsieh, Chi-Feng
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Chang, Edward-Yi
The influence of the thickness of a high-temperature AlN (HT-AlN) buffer layer on the properties of an InAlN/GaN high-electron-mobility transistor (HEMT) grown on a sapphire substrate was investigated. As revealed by atomic force microscope analysis, a rougher surface and larger grain size were observed with a thicker buffer layer. The larger grains promoted the two-dimensional (2D) growth mode of the GaN layer at the initial growth stage. This suppressed oxygen incorporation at the GaN/HT-AlN interface and thus improved the resistivity of the GaN layer. Moreover, the lower grain density also resulted in enhanced GaN crystal quality of the GaN layer. As a consequence, the electrical properties of the InAlN/GaN HEMT device, such as output current, transconductance and off-state breakdown voltage, were improved by increasing the HT-AlN buffer layer thickness. (C) 2015 The Japan Society of Applied Physics
Investigation of TMAl preflow to the properties of AlN and GaN film grown on Si(111) by MOCVD
(2014-01-01)
Lumbantoruan, Franky
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Wong, Yuan-Yee
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Wu, Yue-Han
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Huang, Wei-Ching
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Shrestra, Niraj Man
The influence of TMAl preflow to the AlN buffer layer and GaN thin film was studied by Optical Microscope, Atomic Force Microscope, X-ray diffraction and Transmission Electron Microscope. Different duration of TMAl preflow lead to substantially differences of the AlN buffer layer and GaN film properties in terms of surface morphology and crystal quality. It was found without TMAl preflow the crystal quality of AlN buffer layer and GaN deteriorated due to the formation of amorphous interlayer between Si and AlN. Meltback etching and cracks was observed on the surface of GaN grown on AlN without TMAl preflow. However, overlong duration of TMAl preflow degraded the properties of AlN buffer layer and the subsequent GaN layer. GaN grown with longer TMAl preflow suffer of poor crystal quality, high density cracks and rough surface morphology. With the optimum duration of TMAl preflow, crystal quality and surface roughness of GaN can be improved.
Investigations of GaN growth on the sapphire substrate by MOCVD method with different AlN buffer deposition temperatures
(2016-04)
Huang, Wei-Ching
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Chu, Chung-Ming
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Wong, Yuen Yee
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Chen, Kai-Wei
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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.
MOVPE high quality GaN film grown on Si (111) substrates using a multilayer AlN buffer
(2008)
Lin, Kung-Liang
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Chang, Edward-Yi
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Huang, Jui-Chien
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Huang, Wei-Ching
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Hsiao, Yu-Lin
High quality GaN films were successfully grown on Si (111) substrates using the MOVPE method and a multilayer AlN buffer. The buffer layer film quality and thickness are critical for the growth of the crack-free GaN film on Si (111) substrates. Cracks started to form on the single layer high temperature (HT) AlN film, grown on Si (111) substrate as the AlN thickness was greater than 20 nm. However, a 100 nm crack-free AlN film, can be obtained when multilayer buffer of HT-AlN/low temperature (LT)-AlN/HT-AlN was grown on the Si(111) substrate. By using multilayer AlN buffer, a 2 mu m crack-free GaN film was successful grown on the 2 '' Si (111) substrate. Moreover, the GaN film (2 mu m thick) grown on Si with a GaN (004) Mosaic FWHM of only 0.12 degrees.
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
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Chu, Chung-Ming
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Hsieh, Chi-Feng
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Wong, Yuen-Yee
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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.
The effects of Growth Parameters on the Electrical Properties in InAlN/AlN/GaN High-Electron-Mobility Transistors (HEMTs)
(2014-01-01)
Huang, Wei-Ching
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Wong, Yuen-Yee
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Liu, Kuan-Shin
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Hsieh, Chi-Feng
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Chang, Edward Yi
The electrical properties in the InAlN/AlN/GaN high electron mobility transistor grown by metal-organic vapor deposition (MOCVD) with different growth parameters were investigated in this study. We observed that two-dimensional electron gas (2DEG) channel was influenced by thickness of AlN spacer layer and a stable stage prior to the growth of AlN spacer layer. The TEM images showed the generation of dislocations at interface between AlN/GaN and InAlN/AlN with the thicker AlN spacer layer. These dislocations acted as electron scattering center and degraded the electron mobility in the 2DEG channel. Besides, a too long stable stage also appeared degradation in the electron mobility due to the etching effect of H-2 gas. By optimizing growth parameters, the highest electron mobility of 890 cm(2)/V.s
The Parasitic Reaction During the MOCVD Growth of AlInN Material
(2012-01-01)
Huang, Wei-Ching
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Wong, Yuen-Yee
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Liu, Kusan-Shin
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Hsieh, Chi-Feng
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Chang, Edward Yi
For observation of parasitic reaction effect during InAlN material growth by Matel-Organic Chemical Vapor Deposition (MOCVD), the growth parameters include temperature and pressure had been varied to investigate it. The pressure would be kept at 50torr, 100torr and 150torr and temperature was varied from 700 degrees C to 780 degrees C by 20 degrees C step in each growth pressure. The experimental results appeared that higher pressure gave rise to more serious parasitic reaction during material growth. It made the less Al atoms incorporate into the AllnN. In addition the 100torr growth pressure shows the best efficiency of Al atom incorporation compare with other two growth pressures. By the AFM analysis, the morphology of Al0.82In0.18N grown with three different pressures was also examined.