Browsing by Author "Yang, Chu-Shou"

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Carrier relaxation of ZnCdSe/ZnSe quantum wells
(2008-09-01)
Jang, Der-Jun
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Lee, Meng-En
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Chung, Yung-Hsien
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Yang, Chu-Shou
;
Chou, Wu-Ching
The energy relaxations of Zno(0.91)Cd(0.09)Se multiquantum wells and epilayer structures were studied with an ultrafast time-resolved photoluminescence apparatus. The increase in the rise time of photoluminescence with decreasing photon energy and the redshift of the peak energy of time-resolved photoluminescence spectra with the delay time are attributed to the band-filling effect and energy relaxation of hot carriers. The derived carrier temperature decreases rapidly within the first 10 ps after photoexcitation and tit a much slower rate thereafter. The fast carrier cooling can be explained by the longitudinal optical (LO) phonon emissions by carriers through the Frohlich interaction. The obtained effective scattering times of carrier and LO phonons are comparable to the theoretical prediction of 20 fs for multi-quantum well (MQW) of 20 nm well thickness and the epilayer. The slow carrier capture process may account for the long effective scattering time of 35 fs for the MQWs of 5 nm well thickness.
Depth-Profiling Electronic and Structural Properties of Cu(In,Ga)(S,Se)(2) Thin-Film Solar Cell
(2016-09-14)
Chiang, Ching-Yu
;
Hsiao, Sheng-Wei
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Wu, Pin-Jiun
;
Yang, Chu-Shou
;
Chen, Chia-Hao
Utilizing a scanning photoelectron microscope (SPEM) and grazing-incidence X-ray powder diffraction (GIXRD), we studied the electronic band structure and the crystalline properties of the pentanary Cu(In,Ga)(S,Se)(2) (CIGSSe) thin-film solar cell as a function of sample depth on measuring the thickness-gradient sample. A novel approach is proposed for studying the depth-dependent information on thin films, which can provide a gradient thickness and a wide cross-section of the sample by polishing process. The results exhibit that the CIGSSe absorber layer possesses four distinct stoichiometries. The growth mechanism of this distinctive compositional: distribution formed by a two stage process is described according to the thermodynamic reaction and the manufacturing, process. On the basis of the depth-profiling results, the gradient profiles of the conduction and valence bands were constructed to elucidate the performance of the electrical properties (in this case, V-oc = 620 mV, J(sc) = 34.6 mA/cm(2), and eta = 14.04%); the valence-band maxima (VBM) measured with a SPEM in the spectroscopic mode coincide with this band-structure model, except for a lowering of the VBM observed in the surface region of the absorber layer due to the ordered defect compound (ODC). In addition, the depth-dependent texturing X-ray diffraction pattern presents the crystalline quality and the residual stress for each depth of a thin-film device. We find that the randomly oriented grains in the bottom region of the absorber layer and the different residual stress between the underlying Mo and the absorber interface, which can deteriorate the electrical performance due to peeling-off effect. An anion interstitial defect can be observed on comparing the anion concentration, of the elemental distribution with crystalline composition; a few excess sulfur atoms insert in interstitial sites at the front side of the absorber layer, whereas the interstitial selenium atoms insert at the back side.
Effect of microstructure on the nanomechanical properties of Zn(1-x)Cd(x)Se alloys
(2010-01-15)
Wen, Hua-Chiang
;
Yang, Chu-Shou
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Chou, Wu-Ching
;
電子物理學系
;
Department of Electrophysics
We present a study of the nanoindentation behavior of Zn(1-x)Cd(x)Se epilayers grown using molecular beam epitaxy; the surface roughness, microstructure, and crystallinity were analyzed using atomic force microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction; the hardness H and elastic modulus E were studied using nanoindentation techniques. We found that these highly crystalline materials possessed no stacking faults or twins in their microstructures. We observed a very marked increase in the value of H and a significant decrease in the value of E upon increasing the concentration of Cd, presumably because of an increase in the stiffness of the CdSe bond relative to that of the ZnSe bond. We observed a corresponding shrinkage of the contact-induced damage area for those films having a small grain size and a higher value of H. It appears that resistance against contact-induced damage requires a higher Cd concentration. (C) 2009 Elsevier B.V. All rights reserved.
Effect of microstructure on the nanomechanical properties of Zn1-xCdxSe alloys
(2010-01-15)
Wen, Hua-Chiang
;
Yang, Chu-Shou
;
Chou, Wu-Ching
;
電子物理學系
;
Department of Electrophysics
We present a study of the nanoindentation behavior of Zn1-xCdxSe epilayers grown using molecular beam epitaxy; the surface roughness, microstructure, and crystallinity were analyzed using atomic force microscopy, cross-sectional transmission electron microscopy, and X-ray diffraction; the hardness H and elastic modulus E were studied using nanoindentation techniques. We found that these highly crystalline materials possessed no stacking faults or twins in their microstructures. We observed a very marked increase in the value of H and a significant decrease in the value of E upon increasing the concentration of Cd, presumably because of an increase in the stiffness of the CdSe bond relative to that of the ZnSe bond. We observed a corresponding shrinkage of the contact-induced damage area for those films having a small grain size and a higher value of H. It appears that resistance against contact-induced damage requires a higher Cd concentration. (C) 2009 Elsevier B.V. All rights reserved.
Effects of isomeric transformation on characteristics of Alq3 amorphous layers prepared by vacuum deposition at various substrate temperatures
(2007-06-15)
Jian, Zhi-An
;
Luo, Ying-Zi
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Chung, Jia-Ming
;
Tang, Shiow-Jing
;
Kuo, Ming-Chin
Organic tris(8-hydroxyquinoline)aluminum (Alq3) amorphous layers are prepared by vacuum deposition at various substrate temperatures T-sub from 30 to 180 degrees C. The surface morphology and electrical characteristics of these as-deposited layers are studied by atomic force microscopy and current-density versus electric-field (J-E) curves. The temperature dependence of the dark electrical conductivity sigma(T) determined from J-E curves is also examined. These experimental results reveal that the surface and electrical properties of Alq3 amorphous layers deposited at T-sub between 90 and 120 degrees C exhibit an anomalous T-sub dependence. However, this anomalous T-sub dependence is not observed from infrared absorption measurements, and therefore is not the result of chemical degradation. The observed behavior is explained in terms of the property that the vacuum deposition of Alq3 with T-sub between 90 and 120 degrees C involves a thermal interconversion between meridional and facial Alq3 isomers. (c) x 2007 American Institute of Physics.
Effects of source and substrate temperatures on the properties of ITO/CuPc/C-60 heterostructure prepared by physical vapor deposition
(2008-04-01)
Chiu, Kuan-Cheng
;
Juey, Liu-Ting
;
Su, Chih-Feng
;
Tang, Shiow-Jing
;
Jong, Ming-Nan
Small-molecule organic photovoltaic (OPV) cells with a heterostructure of indium tin oxide (ITO)/copper phthalocyanine (CuPc)/C-60/Ag were fabricated by physical vapor deposition at different source temperatures T-sou and substrate temperatures T-sub. The physical properties of these as-deposited organic thin films including surface morphology, structural information, and electrical and optical properties were measured (in layer-by-layer sequence) by atomic force microscopy, X-ray diffraction, current-voltage characteristics, and electronic absorption spectra. At first, the effects of different deposition conditions (Tsou and Tsub) on growth rate and film thickness of these organic thin films were examined. Then, the interface properties of ITO/CuPc and CuPc/C-60 were studied with respect to T-sub. Short-circuit current density J(sc) and open-circuit voltage V c for this ITO/CuPc/C-60/Ag heterostructure under illumination were performed, and the spectral response of J(sc) was analyzed. Finally, the Tub-dependence of the physical properties of the as-deposited organic films and of the performance of the as-fabricated OPV cells were discussed. (c) 2007 Elsevier B.V. All rights reserved.
Epitaxial single-crystal of GaSe epilayers grown on a c-sapphire substrate by molecular beam epitaxy
(2015-10-01)
Wu, Chia-Hsin
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Yang, Chu-Shou
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Wang, Yen-Chi
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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.
Evaluating the abrasive wear of Zn(1-x)Mn(x)O heteroepitaxial layers using a nanoscratch technique
(2010-08-01)
Chang, Yu-Ming
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Wen, Hua-Chiang
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Yang, Chu-Shou
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Lian, Derming
;
Tsai, Chien-Huang
In this study, we used nanoscratch techniques under a ramping load to evaluate the abrasive wear of Zn(1-x)Mn(x)O epilayers (0 <= x <= 0.16) grown through molecular beam epitaxy (MBE) on sapphire substrates. We analyzed the surface roughness and damage using atomic force microscopy (AFM) and nano-indenter techniques. The scratched surfaces of the Zn(1-x)Mn(x)O epilayers were significantly different for the various Mn compositions. AFM imaging of the Zn(1-x)Mn(x)O films revealed that pileup phenomena were important on both sides of each scratch. During the scratching process, we found that cracking dominated in the case of Zn(1-x)Mn(x)O films while ploughing; also we observed lower values of the coefficient of friction and shallower penetration depths for the films upon increasing the Mn content (x) from 0 to 0.16, suggesting that higher Mn contents provided the Zn(1-x)Mn(x)O epilayers with higher shear resistances, enhanced by the presence of MnO bonds. (C) 2010 Elsevier Ltd. All rights reserved.
Evaluating the abrasive wear of Zn1-xMnxO heteroepitaxial layers using a nanoscratch technique
(2010-08-01)
Chang, Yu-Ming
;
Wen, Hua-Chiang
;
Yang, Chu-Shou
;
Lian, Derming
;
Tsai, Chien-Huang
In this study, we used nanoscratch techniques under a ramping load to evaluate the abrasive wear of Zn1-xMnxO epilayers (0 <= x <= 0.16) grown through molecular beam epitaxy (MBE) on sapphire substrates. We analyzed the surface roughness and damage using atomic force microscopy (AFM) and nano-indenter techniques. The scratched surfaces of the Zn1-xMnxO epilayers were significantly different for the various Mn compositions. AFM imaging of the Zn1-xMnxO films revealed that pileup phenomena were important on both sides of each scratch. During the scratching process, we found that cracking dominated in the case of Zn1-xMnxO films while ploughing; also we observed lower values of the coefficient of friction and shallower penetration depths for the films upon increasing the Mn content (x) from 0 to 0.16, suggesting that higher Mn contents provided the Zn1-xMnxO epilayers with higher shear resistances, enhanced by the presence of MnO bonds. (C) 2010 Elsevier Ltd. All rights reserved.
Mechanical properties of InGaN thin films deposited by metal-organic chemical vapor deposition
(2008-06-15)
Jian, Sheng-Rui
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Jang, Jason Shian-Ching
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Lai, Yi-Shao
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Yang, Ping-Feng
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Yang, Chu-Shou
We report in this study characteristics of InGaN thin films developed by metal-organic chemical vapor deposition (MOCVD) at various growth temperatures. The effect of deposition temperatures on microstructures and mechanical properties are examined using X-ray diffraction (XRD), scanning probe microscopy (SPM), and nanoindentation techniques. The XRD analysis shows no evidence of phase separation for InGaN thin films. The SPM micrographs indicate that the films have relatively smooth surfaces. Hardness and Young's modulus of InGaN thin films vary according to the deposition temperature. As the deposition temperature increases from 730 to 790 degrees C, the grain size increases from 28 to 52 nm. Hardness for InGaN thin films dropped from 13.8 to 17.6 GPa in accordance with the increase of the grain size. By fitting experimental data with the Hall-Petch equation, a probable lattice friction stress of 3.48 GPa and Hall-Petch constant of 73.15 GPa nm(1/2) are obtained. (C) 2007 Elsevier B.V. All rights reserved.
Morphological, structural, and mechanical characterizations of InGaN thin films deposited by MOCVD
(2008-09-08)
Yang, Ping-Feng
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Jian, Sheng-Rui
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Lai, Yi-Shao
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Yang, Chu-Shou
;
Chen, Rong-Sheng
Presented in this study are surface roughness, crystalline structure, and nanomechanical properties of InGaN thin films deposited under various growth temperatures, obtained by means of X-ray diffraction (XRD), atomic force microscopy (AFM), and nanoindentation techniques. The InGaN thin films with different In contents were deposited on sapphire substrates through a metal-organic chemical-vapor deposition (MOCVD) system. Changes in mechanical properties for InGaN thin films are discussed in conjunction with deposition temperature, surface morphology and crystalline structure. The XRD measurements showed that there was no phase separation of In as the In composition went from 25 at.% to 34 at.%. Moreover, both XRD and AFM showed larger grain and surface roughness in In0.25Ga0.75N thin films. Nanoindentation results indicate that hardness and Young's modulus both decreased as the indentation depth increased. The contact stress-strain relationships were also analyzed. (C) 2007 Elsevier B.V. All fights reserved.
Nanoscratch study of Zn(1-x)Mn(x)O heteroepitaxial layers
(2010-10-15)
Chang, Yu-Ming
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Chang, Zue-Chin
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Lian, Derming
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Yang, Chu-Shou
;
Yau, Wei-Hung
We investigated the nanotribological properties of Zn(1-x)Mn(x)O epilayers (0 <= x <= 0.16) grown by molecular beam epitaxy (MBE) on sapphire substrates. The surface roughness and friction coefficient (mu) were analyzed by means of atomic force microscopy (AFM) and hysitron triboscope nanoindenter techniques. The nanoscratch system gave the mu value of the films ranging from 0.17 to 0.07 and the penetration depth value ranging 294-200nm when the Mn content was increased from x = 0 to 0.16. The results strongly indicate that the scratch wear depth under constant load shows that higher Mn content leads to Zn(1-x)Mn(x)O epilayers with higher shear resistance, which enhances the Mn-O bond. These findings reveal that the role of Mn content on the growth of Zn(1-x)Mn(x)O epilayers can be identified by their nanotribological behavior. (C) 2010 Elsevier B.V. All rights reserved.
Nanoscratch study of Zn1-xMnxO heteroepitaxial layers
(2010-10-15)
Chang, Yu-Ming
;
Chang, Zue-Chin
;
Lian, Derming
;
Yang, Chu-Shou
;
Yau, Wei-Hung
We investigated the nanotribological properties of Zn1-xMnxO epilayers (0 <= x <= 0.16) grown by molecular beam epitaxy (MBE) on sapphire substrates. The surface roughness and friction coefficient (mu) were analyzed by means of atomic force microscopy (AFM) and hysitron triboscope nanoindenter techniques. The nanoscratch system gave the mu value of the films ranging from 0.17 to 0.07 and the penetration depth value ranging 294-200nm when the Mn content was increased from x = 0 to 0.16. The results strongly indicate that the scratch wear depth under constant load shows that higher Mn content leads to Zn1-xMnxO epilayers with higher shear resistance, which enhances the Mn-O bond. These findings reveal that the role of Mn content on the growth of Zn1-xMnxO epilayers can be identified by their nanotribological behavior. (C) 2010 Elsevier B.V. All rights reserved.
Optical and Electrical Characterizations of ZnMnO Thin Films on c-Al(2)O(3)
(2009-04-01)
Lin, Hung-Ji
;
Lin, Der-Yuh
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Wu, Jenq-Shinn
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Yang, Chu-Shou
;
Chou, Wu-Ching
We have studied the manganese (Mn) composition dependence of the optical and electrical properties of ZnMnO thin films, which are grown on c-Al(2)O(3) substrates by plasma-assisted molecular beam epitaxy (PAMBE). The lattice constant and grain size are estimated by Xray diffraction (XRD), and it is found that the lattice constant increases and the grain size decreases with increasing Mn composition. When more Mn is incorporated into the ZnMnO thin films, a blue shift of the absorption edges and photoluminescence emission peaks are observed. Hall measurement shows n-type conduction behavior for all the samples. The decrease in mobility might be related with the increase in the number of impurity scattering centers, and the decrease in the carrier concentration can be attributed to the carrier quenching effect induced by the deep-level defects. The ac electrical response of ZnMnO is studied by impedance spectroscopy (IS). The equivalent RC circuit and parameters of the grain and grain boundary are determined. (C) 2009 The Japan Society of Applied Physics
Optical and Electrical Characterizations of ZnMnO Thin Films on c-Al2O3
(2009-04-01)
Lin, Hung-Ji
;
Lin, Der-Yuh
;
Wu, Jenq-Shinn
;
Yang, Chu-Shou
;
Chou, Wu-Ching
We have studied the manganese (Mn) composition dependence of the optical and electrical properties of ZnMnO thin films, which are grown on c-Al2O3 substrates by plasma-assisted molecular beam epitaxy (PAMBE). The lattice constant and grain size are estimated by Xray diffraction (XRD), and it is found that the lattice constant increases and the grain size decreases with increasing Mn composition. When more Mn is incorporated into the ZnMnO thin films, a blue shift of the absorption edges and photoluminescence emission peaks are observed. Hall measurement shows n-type conduction behavior for all the samples. The decrease in mobility might be related with the increase in the number of impurity scattering centers, and the decrease in the carrier concentration can be attributed to the carrier quenching effect induced by the deep-level defects. The ac electrical response of ZnMnO is studied by impedance spectroscopy (IS). The equivalent RC circuit and parameters of the grain and grain boundary are determined. (C) 2009 The Japan Society of Applied Physics
Optical and Magnetic Properties of Zn1-xMnxO Grown by Plasma-Assisted Molecular Beam Epitaxy
(2014-06-01)
Chou, Wu Ching
;
Tzou, An-Jye
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Chen, Hsuan-Shao
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Chien, Kun-Feng
;
Fan, Wen-Chung
Zn1-xMnxO films (0 <= x <= 0.070) were grown by plasma-assisted molecular beam epitaxy on Si substrates with AlN buffer layers. For low Mn concentration samples, x <= 0.02, photoluminescence spectra show strong near band edge emission. Strong phonon and exciton coupling-induced resonant Raman scattering was observed. Paramagnetic, antiferromagnetic, and ferromagnetic phases were observed. Room temperature ferromagnetism for all samples was attributed to the bound magnetic polaron effect.
Origin of localized states in zinc-blende ZnCdSe thin films and the influence on carrier relaxation of self-assembled ZnTe/ZnCdSe quantum dots
(2015-05-25)
Lee, Ling
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Dai, Yue-Ru
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Yang, Chu-Shou
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Fan, Wen-Chung
;
Chou, Wu-Ching
This study discovered the origin of deep level emission in zinc-blende ZnCdSe thin films grown by molecular beam epitaxy, in which a localization behavior was noticed. Pronounced deep level emission observed in films grown under a VI/II ratio of 1.74 (Se-accumulated regime) could be suppressed by a lower VI/II ratio of 1.04 (intermediate regime) and 0.74 (metal-rich regime). Hence the localized states could be correlated to excess selenium accumulated at the growth surface. The localized states also influence the carrier relaxation process of self-assembled ZnTe quantum dots embedded in a ZnCdSe matrix. Once quantum dots surmount the wetting layer, localized electrons in the capping layer dominate the type-II transition and exhibit size-independent lifetimes. (C) 2015 Elsevier B.V. All rights reserved.
Photoluminescence characterization of type-II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures
(2007-04-01)
Shiu, Jian-Jhin
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Chen, Wei-Li
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Lin, Der-Yuh
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Yang, Chu-Shou
;
Chou, Wu-Ching
The optical characterization of type-II Zn0.97Mn0.03Se/ZnSe0.92Te0.08 multiple-quantum-well structures has been studied using photoluminescence (PL), temperature-dependent PL, and power-dependent PL. The PL data reveal that the band alignment of the ZnMnSe/ZnSeTe multiple quantum wells (MQWs) is type II. In comparison with the theoretical calculation based on solving the Schrodinger equation of a square potential well, the valence band offset is estimated to be 0.6 eV. From the power-dependent PL spectra, it is observed that the peak position of PL spectra shows a blue shift on increasing the excitation power. The blue shift can be interpreted in terms of the band-bending effect due to spatially separated carriers in a type-II alignment and the band filling effect. The thermal activation energy (EA) for quenching the PL intensity was determined from temperature-dependent PL spectra. The thermal activation energy was found to decrease as the thickness of ZnMnSe or ZnSeTe layers decreased.
The influences of H-2 plasma pretreatment on the growth of vertically aligned carbon nanotubes by microwave plasma chemical vapor deposition
(2008-06-01)
Jian, Sheng-Rui
;
Chen, Yuan-Tsung
;
Wang, Chih-Feng
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Wen, Hua-Chiang
;
Chiu, Wei-Ming
The effects of H-2 flow rate during plasma pretreatment on synthesizing the multiwalled carbon nanotubes (MWCNTs) by using the microwave plasma chemical vapor deposition are investigated in this study. A H-2 and CH4 gas mixture with a 9:1 ratio was used as a precursor for the synthesis of MWCNT on Ni-coated TaN/Si(100) substrates. The structure and composition of Ni catalyst nanoparticles were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The present findings showed that denser Ni catalyst nanoparticles and more vertically aligned MWCNTs could be effectively achieved at higher flow rates. From Raman results, we found that the intensity ratio of G and D bands (I-D/I-G) decreases with an increasing flow rate. In addition, TEM results suggest that H-2 plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles. As a result, the pretreatment plays a crucial role in modifying the obtained MWCNTs structures.