Browsing by Author "Ho, Yen-Teng"

Now showing 1 - 20 of 53

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.
Atomic layer deposition of epitaxial ZnO on GaN and YSZ
(2007-01-01)
Lin, Chih-Wei
;
Ke, Dong-Jie
;
Chao, Yen-Cheng
;
Chang, Li
;
Liang, Mei-Hui
ZnO thin films were epitaxially grown by atomic layer deposition on both of GaN/c-sapphire and yttria-stabilized zirconia (YSZ) substrates for comparison. X-ray diffraction, cross-sectional transmission electron microscopy (TEM) and photoluminescence (PL) measurements show that epitaxial ZnO films have better structural qualities and optical properties on GaN than on YSZ, whereas atomic force microscopy (AFM) shows that the surface of ZnO films on YSZ is smoother than on GaN. From the ZnO thickness measured by TEM, the growth rate of ZnO on GaN is about one (0 0 0 2) monolayer per cycle, which is roughly four times of that on YSZ. (c) 2006 Elsevier B.V. All rights reserved.
BUFFER-OPTIMIZED IMPROVEMENT IN RF LOSS OF ALGAN/GAN HEMTS ON 4-INCH SILICON (111)
(2017-01-01)
Luong, Tien Tung
;
Lumbantoruan, Franky
;
Chen, Yen-Yu
;
Ho, Yen-Teng
;
Lin, Yueh-Chin
The effect of different buffer layers on the RF losses of GaN-based high-mobility-transistors (HEMTs) on Si substrate has been studied. It is found that the electron inversion layer induced by the residual tensile stress in AlN buffer is responsible for a dominant loss factor. It is first time such mechanisms of the RF loss of GaN/Si is discussed. It is proven that using a thin high-low-high temperature (HLH) AlN buffer reducing the tensile stress in AlN consequently reduces the RF loss.
Complex Optical Conductivity of Two-Dimensional MoS2 : A Striking Layer Dependency
(2019-10-17)
Song, Baokun
;
Gu, Honggang
;
Fang, Mingsheng
;
Ho, Yen-Teng
;
Chen, Xiuguo
The complex optical conductivities of two-dimensaionl (2D) materials are fundamental for extended applications of related optoelectronic devices. Here, we systematically investigate the layer-dependent evolutions in the complex optical conductivities of 1-6 layer 2D MoS2 over an ultrawide spectral range (0.73-6.42 eV) by spectroscopic ellipsometry. We identify five feature peaks (A-E) in the optical conductivity spectra, which present interesting layer dependencies due to the scaling effect. Results suggest that the center energies of peaks A and B are nearly layer-independent, while those of peaks C and D exhibit redshifts as the layer increases. We interpret these layer-dependent evolutions as the competition between the decreasing exciton effect and the prominent band shrinkage with the increasing layer number. Additionally, the applicability of the classical slab model and the surface current model in evaluating the optical conductivities of 2D MoS2 with different layers is discussed from an experimental perspective.
Contact resistance reduction on layered MoS2 by Ar plasma pre-treatment
(2016)
Ho, Yen-Teng
;
Chu, Yung-Ching
;
Jong, Chao An
;
Chen, Hung-Yi
;
Lin, Meng-Wei
The effect of resistance (Rc) reduction of Ti/Au contact on MoS2 by ICP Ar plasma pretreatment is presented. The lowest Rc of 1.72 ohm-cm was achieved with the ICP treatment condition of 50W (ICP) /2W (chuck) for 10 sec. Compared with the contact without treatment (19.6 ohm-cm), the Rc improves over 10 times, demonstrating the advantage of Ar plasma pre-treatment on MoS2 contact.
Defects in m-plane ZnO epitaxial films grown on (112) LaAlO(3) substrate
(2011-05-01)
Wang, Wei-Lin
;
Peng, Chun-Yen
;
Ho, Yen-Teng
;
Chuang, Shu-Chang
;
Chang, Li
The crystallographic orientations of m-plane ZnO on (112) LaAlO(3) (LAO) substrate are [(1) over bar2 (1) over bar0](ZnO)parallel to[11 (1) over bar](LAO) and [0001](ZnO)parallel to[(1) over bar 10](LAO). The defects in m-plane ZnO have been systematically investigated using cross section and plan-view transmission electron microscopy (TEM). High-resolution TEM observations in cross section show misfit dislocations and basal stacking faults (BSFs) at the ZnO/LAO interface. In the films, threading dislocations (TDs) with 1/3 < 11 (2) over bar0 > Burgers vectors are distributed on the basal plane, and BSFs have 1/6 < 20 (2) over bar3 > displacement vector. The densities of dislocations and BSFs are estimated to be 5.1 x 10(10) cm(-2) and 4.3 x 10(5) cm(-1), respectively. In addition to TDs and BSFs, plan-view TEM examination also reveals that stacking mismatch boundaries mainly lie along the m-planes and they connect with planar defect segments along the r-planes. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3539046]
Defects in m-plane ZnO epitaxial films grown on (112) LaAlO3 substrate
(2011-05-01)
Wang, Wei-Lin
;
Peng, Chun-Yen
;
Ho, Yen-Teng
;
Chuang, Shu-Chang
;
Chang, Li
The crystallographic orientations of m-plane ZnO on (112) LaAlO3 (LAO) substrate are [(1) over bar2 (1) over bar0](ZnO)parallel to[11 (1) over bar](LAO) and [0001](ZnO)parallel to[(1) over bar 10](LAO). The defects in m-plane ZnO have been systematically investigated using cross section and plan-view transmission electron microscopy (TEM). High-resolution TEM observations in cross section show misfit dislocations and basal stacking faults (BSFs) at the ZnO/LAO interface. In the films, threading dislocations (TDs) with 1/3 < 11 (2) over bar0 > Burgers vectors are distributed on the basal plane, and BSFs have 1/6 < 20 (2) over bar3 > displacement vector. The densities of dislocations and BSFs are estimated to be 5.1 x 10(10) cm(-2) and 4.3 x 10(5) cm(-1), respectively. In addition to TDs and BSFs, plan-view TEM examination also reveals that stacking mismatch boundaries mainly lie along the m-planes and they connect with planar defect segments along the r-planes. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3539046]
Defects in nonpolar (13(4)over-bar0) ZnO epitaxial film grown on (114) LaAlO3 substrate
(2014-03-01)
Yen, Tzu-Chun
;
Wang, Wei-Lin
;
Peng, Chun-Yen
;
Tian, Jr-Sheng
;
Ho, Yen-Teng
The defects in (13 (4) over bar0)ZnO epitaxial film grown on (114)LaAlO3 (LAO) have been systematically investigated by using transmission electron microscopy. At the ZnO/LAO interface, the Burgers vectors of misfit dislocations are identified to be 1/3[(1) over bar2 (1) over bar0] and 1/2[0001]. Threading dislocations with the Burgers vectors of 1/3 < 11 (2) over bar0 > and < 0001 > are distributed on the basal plane. In (13 (4) over bar0)ZnO film, the predominant planar defects are basal stacking faults (BSFs) with 1/6 < 20 (2) over bar3 > displacement vectors. The densities of dislocations and BSFs are about 3.8 x 10(10) cm(-2) and 3.1 x 10(5) cm(-1), respectively. (C) 2014 American Vacuum Society.
Defects in semipolar (11(2)over-bar(2)over-bar) ZnO grown on (112) LaAlO3/(La, Sr) (Al, Ta)O-3 substrate by pulsed laser deposition
(2013-03-27)
Tian, Jr-Sheng
;
Wu, Yue-Han
;
Peng, Chun-Yen
;
Chiu, Kun-An
;
Shih, Yi-Sen
The microstructure of semipolar (11 (2) over bar(2) over bar) ZnO deposited on (112) LaAlO3/(La, Sr) (Al, Ta)O-3 was investigated by transmission electron microscopy. The ZnO shows an in-plane epitaxial relationship of [11 (2) over bar3](ZnO) parallel to [11 (1) over bar](LAO/LSAT) with oxygen-face sense polarity. The misfit strain along [11 (2) over bar3](ZnO) and [1 (1) over bar 00](ZnO) is relieved through the formation of misfit dislocations with the Burgers vectors b = 1/6[11 (2) over bar3](ZnO) and b = 1/3 < 1 (2) over bar 10 >(ZnO), respectively. The line defects in the semipolar ZnO are predominantly perfect dislocations, and the dislocation density decreases with increasing ZnO thickness as a result of dislocation reactions. Planar defects were observed to lie in the M-plane and extend along < 0001 >, whereas basal stacking faults were rarely found.
Effect of growth temperature on a-plane ZnO formation on r-plane sapphire
(2011-05-01)
Peng, Chun-Yen
;
Tian, Jr-Sheng
;
Wang, Wei-Lin
;
Ho, Yen-Teng
;
Chuang, Shu-Chang
The effect of growth temperature on a-plane ZnO formation on r-plane sapphire has been systematically investigated by employing in situ high pressure reflection high-energy electron diffraction, atomic force microscopy, and high-resolution x-ray diffraction. For film growth above and below 600 degrees C, it is shown that there is a significant difference in growth rate and surface morphology due to the differences in the growth mode. Stripelike morphologies were observed on the surface of a-plane ZnO grown at low temperature (LT) because of differences in the growth rate along the c-axis and the growth rate normal to the c-axis. Furthermore, annealing of films grown at low temperature results in more pronounced stripe morphology and in improvement of crystallinity. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3549141]
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.
Epitaxial single-crystal of GaSe epilayers grown on a c-sapphire substrate by molecular beam epitaxy
(2015-10-01)
Wu, Chia-Hsin
;
Yang, Chu-Shou
;
Wang, Yen-Chi
;
Huang, Hsi-Jung
;
Ho, Yen-Teng
In this study, hetero-epitaxy of GaSe epilayers on a c-sapphire substrate achieved using molecular beam epitaxy was demonstrated. The GaSe epitaxial growth was monitored using in situ reflection high-energy electron diffraction (RHEED). Streak RHEED patterns showed a flat and highly crystalline situation. Furthermore, two RHEED patterns were observed after 15min of growth, and they were correlated with the m-axis and a-axis of hexagonal GaSe. The single crystal of GaSe was verified using X-ray diffraction and high-resolution cross-section transmission electron microscopy. The full width at half-maximum of (0002) in the XRD rocking-curve spectrum of GaSe epilayer is obtain around 207arcsec, which is the smallest value observed to date. The epitaxial growth of GaSe demonstrated the feasibility of growing large-area epilayers.
Epitaxy of m-plane ZnO on (112) LaAlO(3) substrate
(2009-05-01)
Ho, Yen-Teng
;
Wang, Wei-Lin
;
Peng, Chun-Yen
;
Chen, Wei-Chun
;
Liang, Mei-Hui
Heteroepitaxial growth of non-polar in-plane (10 (1) over bar0) ZnO has been demonstrated on (112) LaAlO(3) single crystal substrates using the pulsed laser deposition method. X-ray diffraction, reflection high energy electron diffraction, and cross-sectional transmission electron microscopy with selected-area diffraction, have been used to characterize the structural properties of deposited ZnO films. The epitaxial relationship between ZnO and LAO is shown to be (10 (1) over bar0)(ZnO) parallel to (112)(LAO), (11 (2) over bar0)(ZnO) parallel to ((1) over bar(1) over bar1)(LAO), and [0001](ZnO) parallel to [(1) over bar 10](LAO). (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Epitaxy of m-plane ZnO on (112) LaAlO3 substrate
(2009-05-01)
Ho, Yen-Teng
;
Wang, Wei-Lin
;
Peng, Chun-Yen
;
Chen, Wei-Chun
;
Liang, Mei-Hui
Heteroepitaxial growth of non-polar in-plane (10 (1) over bar0) ZnO has been demonstrated on (112) LaAlO3 single crystal substrates using the pulsed laser deposition method. X-ray diffraction, reflection high energy electron diffraction, and cross-sectional transmission electron microscopy with selected-area diffraction, have been used to characterize the structural properties of deposited ZnO films. The epitaxial relationship between ZnO and LAO is shown to be (10 (1) over bar0)(ZnO) parallel to (112)(LAO), (11 (2) over bar0)(ZnO) parallel to ((1) over bar(1) over bar1)(LAO), and [0001](ZnO) parallel to [(1) over bar 10](LAO). (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Experimentally Determining the Top and Edge Contact Resistivities of Two-Step Sulfurization Nb-Doped MoS2 Films Using the Transmission Line Measurement
(2019-10-01)
Chung, Yun-Yan
;
Li, Chi-Feng
;
Lin, Chao-Ting
;
Ho, Yen-Teng
;
Chien, Chao-Hsin
This study determined the top (vertical) and edge (horizontal) resistivities of metal-MoS2 contact based on the experimental results obtained using the transmission line measurement structure. A novel two-step sulfurization scheme was conducted for forming Nb-doped MoS2 films on a sapphire substrate. The edge contact resistivity, rho(C_edge), was almost two orders of magnitude lower than the top contact resistivity, rho(C_top). Our findings highlight a simple and effective method to accurately determine the edge and top contact resistances of a metal-two-dimensional material contact.
Growth and Fabrication of AlGaN/GaN HEMT on SiC Substrate
(2012-01-01)
Wong, Yuen-Yee
;
Chiu, Yu-Sheng
;
Luong, Tien-Tung
;
Lin, Tai-Ming
;
Ho, Yen-Teng
AlGaN/GaN high electron mobility transistor (HEMT) was grown on silicon carbide substrate by metalorganic chemical vapor deposition technique. The AlGaN/GaN structure was optimized by tuning the growth conditions such as AlN buffer thickness, and the Al composition and thickness of AlGaN barrier layer. As a result, the X-ray rocking curve widths were 277 arcsec and 324 arcsec for the GaN (002) and (102) planes, respectively, indicating a high crystalline quality. Hall measurement showed that the AlGaN/GaN structure has a high electron mobility of 1840 (cm(2)/V-s) and a sheet electron concentration of 9.85 x10(12) cm-(2). Besides, HEMT device with sub-micron gate-length (0.7 mu m) was also successfully fabricated. DC measurement showed that the HEMT device has a saturated current of 800 mA/mm, a transconductance of 257 mS/mm and an off-state breakdown voltage larger than 100 V. For RF performance, the device has achieved an output power density (P-out), gain, and power added efficiency (PAE) of 7 W/mm, 23.5 dB and 61.7%, respectively, measured at 2 GHz frequency. On the other hand, the RF performance measured at 8 GHz showed that the device could achieve P-out, gain and PAE of 5.01 W/mm, 14.9 dB and 26.23% respectively.
Growth and structural characterization of ZnO on Y2O3/YSZ by pulsed laser deposition
(2008-03-15)
Lin, Chih-Wei
;
Ho, Yen-Teng
;
Chang, Li
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Pulsed laser deposition was used to form epitaxial Y2O3 buffer layers on yttria-stabilized zirconia (YSZ) (111) substrates, followed by formation of epitaxial ZnO. Structural characterization by X-ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM) shows that Y2O(3) has high-quality crystalline characteristics with a smooth (111) surface, providing a good buffer for deposition of ZnO films on YSZ. For ZnO deposition, a two-step growth process had been adopted, which consisted of low-temperature nucleation and high-temperature growth. ZnO films on Y2O3/YSZ have good structural qualities in c-axis orientation with smooth surfaces. Electron diffraction patterns show an orientation relationship of [2 (1) over bar(1) over bar0](ZnO)//[0 (1) over bar1](Y2O3) and (0002)(ZnO)//(222)(Y2O3). High-resolution TEM clearly reveals that both the interfaces of ZnO/Y2O3 and Y2O3/YSZ are flat without the formation of any interlayers. (C) 2007 Elsevier B.V. All rights reserved.
Growth of a-plane ZnO thin films on LaAlO3(100) substrate by metal-organic chemical vapor deposition
(2008-02-15)
Tian, Jr-Sheng
;
Liang, Mel-Hui
;
Ho, Yen-Teng
;
Liu, Yuan-An
;
Chang, Li
ZnO(1 1 (2) over bar 0) thin films were successfully grown on LaAlO3 (lanthanum aluminate) (10 0) substrate by atmospheric pressure metalorganic chemical vapor deposition. X-ray diffraction, atomic force microscopy, and scanning electron microscopy showed that ZnO films formed at 450 degrees C were composed of almost all (1 1 (2) over bar 0) oriented grains while (0 0 0 2) oriented ZnO grains started to appear at temperature above 550 degrees C. The a-plane ZnO films consisted of two types of domains with their c-axis perpendicular to each other due to LaAlO3(1 0 0) symmetry with low lattice mismatch along < 1 1 0 >. (C) 2007 Elsevier B.V. All rights reserved.
Growth of epitaxial ZnO thin film on yttria-stabilized zirconia single-crystal substrate
(2007-01-01)
Chao, Yen-Cheng
;
Lin, Chih-Wei
;
Ke, Dong-Jie
;
Wu, Yue-Han
;
Chen, Hou-Guang
ZnO growth on yttria-stabilized zirconia (YSZ) (I 1 1) single-crystal substrate has been carried out by metalorganic chemical vapor deposition (MOCVD). High-quality epitaxial ZnO has been evidenced by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Cross-sectional TEM from all deposited films reveals that the interface between ZnO and YSZ is atomically flat, and orientation relationship is deduced to be [1 (1) over bar 100](ZnO//)[11 (2) over bar](YSZ,) (2 (1) over bar(1) over bar0)(ZnO)//[001](YSZ) and (0 0 0 2)(ZnO)//(111)(YSZ). It has been found that surface roughness increases with the substrate temperature in the range of 500-700 degrees C. The growth rate also varies with the temperature. (c) 2006 Elsevier B.V. All rights reserved.