Browsing by Author "Chen, J. R."

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AlGaN/GaN multiple quantum wells grown by atomic layer deposition - art. no. 68941V
(2008)
Lo, M. H.
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Li, Z. Y.
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Chen, J. R.
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Ko, T. S.
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Lu, T. C.
A three-pair AlGaN/GaN multiple quantum well (MQW) structure with superlattices (SLs) was grown on c-plane sapphire using metal organic chemical vapor deposition (MOCVD) system. The AlGaN barrier and GaN well of the MQW structure were grown by atomic layer deposition (ALD) and conventional growth, respectively. The HRTEM and HRXRD results show the grown structure has shape interface between SLs layers and QWs with good periodicity. The AFM and SEM data show smooth surface morphology with low RMS value and low defect density. The CL measurements also indicate uniform luminescence pattern at room temperature. The AlGaN/GaN MQW with AlN/GaN SLs structure grown by ALD could be used to improve the surface morphology by effectively suppress the threading dislocation.
Analysis of parasitic resistance and channel sheet conductance of a-Si : H TFT under mechanical bending
(2007)
Wang, M. C.
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Chang, T. C.
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Liu, Po-Tsun
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Tsao, S. W.
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Chen, J. R.
The effect of mechanical strain on the performance of a-Si: H thin-film transistors (TFTs) with different channel lengths was studied under uniaxial compressive and tensile strain applied parallel to the TFT source-drain current path. The source-drain parasitic resistance and channel sheet conductance were extracted to explain the device performance under mechanical strain. These results indicate that the compressive bending leads to a significant decrease (similar to 16%) in the source-drain parasitic resistance. The channel sheet conductance has shown a 6% variation under mechanical bending. The variation under mechanical bending strain originates from the evolution of defect state density in a-Si:H channel material. (c) 2007 The Electrochemical Society.
Blue GaN-based vertical cavity surface emitting lasers by CW current injection at 77K
(2009)
Kuo, H. C.
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Chen, S. W.
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Kao, T. T.
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Kao, C. C.
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Chen, J. R.
In the paper, we describe the fabrication and performance characteristics of GaN-based vertical-cavity surface-emitting lasers (VCSELs) by optical pumping and current injection. According to the employment of high-quality and high-reflectivity AlN/GaN DBRs in the whole structure, the lasing action of optically pumped GaN-based VCSELs with hybrid mirrors has been observed at room temperature. Due to the excellent results of optically pumped GaN-based VCSELs with hybrid mirrors, we further demonstrated the lasing behavior of GaN-based VCSELs by continuous-wave current injection at 77 K. The laser has one dominated blue wavelength located at 462 nm with a linewidth of about 0.15 nm and the threshold injection current at 1.4 mA. The divergence angle and polarization ratio of the GaN-based VCSELs with hybrid mirrors are about 11.7 degrees and 80 %, respectively. A larger spontaneous coupling efficiency of about 7.5x10(-2) was also measured.
Characteristics of a-plane GaN with the SiN(x) insertion layer grown by metal-organic chemical vapor deposition
(2008-11-15)
Ko, T. S.
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Wang, T. C.
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Huang, H. M.
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Chen, J. R.
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Chen, H. G.
We utilized in-situ-grown SiN(x) insertion layers to mitigate part of dislocations stretching in nonpolar a-plane GaN films using metal-organic chemical vapor deposition. Both X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements revealed that better crystal quality and smoother surface could be obtained when the in-situ SiN(x) layer was inserted closer to the r-plane sapphire substrate and indicated that the in-situ SiN(x) insertion layer could suppress dislocations caused by lattice mismatch between the sapphire and epitaxial layers. In addition, photoluminescence and cathodoluminescence measurements confirmed the effect of the in-situ SiN(x) insertion layer on the optical properties of the improved a-plane GaN thin film, which is consistent with the XRD and AFM analyses and suggested reduction in the density of nonradiative centers. (C) 2008 Elsevier B.V. All rights reserved.
Characteristics of a-plane GaN with the SiNx insertion layer grown by metal-organic chemical vapor deposition
(2008-11-15)
Ko, T. S.
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Wang, T. C.
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Huang, H. M.
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Chen, J. R.
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Chen, H. G.
We utilized in-situ-grown SiNx insertion layers to mitigate part of dislocations stretching in nonpolar a-plane GaN films using metal-organic chemical vapor deposition. Both X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements revealed that better crystal quality and smoother surface could be obtained when the in-situ SiNx layer was inserted closer to the r-plane sapphire substrate and indicated that the in-situ SiNx insertion layer could suppress dislocations caused by lattice mismatch between the sapphire and epitaxial layers. In addition, photoluminescence and cathodoluminescence measurements confirmed the effect of the in-situ SiNx insertion layer on the optical properties of the improved a-plane GaN thin film, which is consistent with the XRD and AFM analyses and suggested reduction in the density of nonradiative centers. (C) 2008 Elsevier B.V. All rights reserved.
Cu/CuMg gate electrode for the application of hydrogenated amorphous silicon thin-film transistors
(2007)
Wang, M. C.
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Chang, T.-C.
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Liu, Po-Tsun
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Li, Y. Y.
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Xiao, R. W.
The feasibility of using Cu/CuMg as a gate electrode for a-Si:H thin-film transistors (TFTs) has been investigated in this work. The issue of adhesion between the Cu film and glass substrates has been overcome by introducing the Cu/CuMg alloy. Furthermore, a wet-etching process of Cu-based gate metal has been proposed by using the copper etchant in the conventional printed circuit boards. The experimental result showed superior performance of a-Si:H TFT with desired electrode taper angle and minimal loss of critical dimension. The a-Si:H TFT exhibited mobility of 0.37 cm(2)/V s, subthreshold slope of 0.83 V/dec, and V(th) of 2.02 V.
Effect of Laser Welding on Properties of Dissimilar Joint of Al-Mg-Si and Al-Mn Aluminum Alloys
(2010-03-01)
Chang, C. C.
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Chou, C. P.
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Hsu, S. N.
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Hsiung, G. Y.
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Chen, J. R.
This study discusses the welding properties for the components of an aluminum-alloy ultra-high vacuum chamber and beam position monitor (BPM). The welding parameters include the modes of laser output (pulsed wave and continuous wave), welding speed, shield gas flow, welding bead structure, and focusing distance. The results showed that the welding defect rate of the pulsed wave type was larger than that of the continuous wave type. The crack in the welding bead reduced with decreasing welding speed. The fusion penetration of the welding bead was higher when the focusing distance was long enough to deepen into the welding material. Weld morphology during the experimental process revealed the proper flow of shield gas. The adaptability design of the welding bead structure in the preceding processes had more effect on overall welding structure and morphology.
Growth and characterization of a-plane Al(x)Ga(1-x)N alloys by metalorganic chemical vapor deposition
(2010-03-01)
Huang, H. M.
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Ling, S. C.
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Chen, J. R.
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Ko, T. S.
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Li, J. C.
The non-polar a-plane Al(x)Ga(1-x)N alloys on GaN epitaxial layer with different Al compositions (0 <= x <= 0.2) were grown on r-plane (1 (1) over bar 0 2) sapphire substrates by using low-pressure metalorganic chemical vapor deposition (MOCVD) and the Al composition x were estimated from the X-ray diffraction measurements. According to the result of asymmetric X-ray reciprocal space mapping, AlGaN layer was coherently strained to the underlying GaN template. The a-plane AlGaN alloy with relatively lower Al composition showed a flat surface with reduction of pits. The best mean roughness of the surface morphology was 1.18 nm. The photoluminescence (PL) result revealed that the PL peak position shifted from 3.42 to 3.87 eV with 0 <= x <= 0.2. Apart from the shifted peak position with increasing Al content, the PL emission intensity and surface morphology of the a-plane AlGaN alloy with relatively low Al content show slightly better characteristics than that of the a-plane GaN and AlGaN with higher Al composition. (C) 2010 Elsevier B.V. All rights reserved.
Growth and characterization of a-plane AlxGa1-xN alloys by metalorganic chemical vapor deposition
(2010-03-01)
Huang, H. M.
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Ling, S. C.
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Chen, J. R.
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Ko, T. S.
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Li, J. C.
The non-polar a-plane AlxGa1-xN alloys on GaN epitaxial layer with different Al compositions (0 <= x <= 0.2) were grown on r-plane (1 (1) over bar 0 2) sapphire substrates by using low-pressure metalorganic chemical vapor deposition (MOCVD) and the Al composition x were estimated from the X-ray diffraction measurements. According to the result of asymmetric X-ray reciprocal space mapping, AlGaN layer was coherently strained to the underlying GaN template. The a-plane AlGaN alloy with relatively lower Al composition showed a flat surface with reduction of pits. The best mean roughness of the surface morphology was 1.18 nm. The photoluminescence (PL) result revealed that the PL peak position shifted from 3.42 to 3.87 eV with 0 <= x <= 0.2. Apart from the shifted peak position with increasing Al content, the PL emission intensity and surface morphology of the a-plane AlGaN alloy with relatively low Al content show slightly better characteristics than that of the a-plane GaN and AlGaN with higher Al composition. (C) 2010 Elsevier B.V. All rights reserved.
Improving Light Output Power of the GaN-Based Vertical-Injection Light-Emitting Diodes by Mg(+) Implanted Current Blocking Layer
(2009-05-01)
Tsai, Min-An
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Yu, Peichen
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Chen, J. R.
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Huang, J. K.
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Chiu, C. H.
A method for forming a current blocking layer (CBL) by ion implantation in GaN-based vertical-injection light-emitting diodes (VI-LEDs) was proposed. It was found that the use of CBL in VI-LEDs can effectively reduce the current crowding effect and enhance the light output power. The uniform emission intensity distribution of VI-LEDs with CBL was demonstrated by electroluminescence measurements. Experimental results show that the wall-plug efficiency was enhanced by 12.3% at an injection current of 20 mA, compared to that of VI-LEDs without CBL, and by 56.2% compared to that of conventional LEDs. The device simulation results reveal that the current path can be blocked by CBL, resulting in high light extraction efficiencies and large current densities within the effective emission region of active layers.
Improving Light Output Power of the GaN-Based Vertical-Injection Light-Emitting Diodes by Mg+ Implanted Current Blocking Layer
(2009-05-01)
Tsai, Min-An
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Yu, Peichen
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Chen, J. R.
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Huang, J. K.
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Chiu, C. H.
A method for forming a current blocking layer (CBL) by ion implantation in GaN-based vertical-injection light-emitting diodes (VI-LEDs) was proposed. It was found that the use of CBL in VI-LEDs can effectively reduce the current crowding effect and enhance the light output power. The uniform emission intensity distribution of VI-LEDs with CBL was demonstrated by electroluminescence measurements. Experimental results show that the wall-plug efficiency was enhanced by 12.3% at an injection current of 20 mA, compared to that of VI-LEDs without CBL, and by 56.2% compared to that of conventional LEDs. The device simulation results reveal that the current path can be blocked by CBL, resulting in high light extraction efficiencies and large current densities within the effective emission region of active layers.
Investigation of Efficiency Droop in Blue InGaN/GaN Light-Emitting Diodes with Different Well Widths
(2010)
Wang, C. H.
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Chiu, C. H.
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Chen, J. R.
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Kuo, H. C.
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Lu, T. C.
Temperature-dependent electroluminescence efficiency of blue light-emitting diodes with different well widths is investigated. The efficiency droop phenomenon for LEDs at low temperature is dependent with electron overflow and non-uniform hole distribution within MQW region. (C) 2010 Optical Society of America
Mechanical bending effect on the photo leakage currents characteristic of amorphous silicon thin film transistors
(2010-11-01)
Wang, M. C.
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Tsao, S. W.
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Chang, T. C.
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Lin, Y. P.
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Liu, Po-Tsun
The photo leakage current (I(PLC)) characteristic of a-Si:H TFTs under different bending strains has been studied. The larger I(PLC) of a-Si:H TFTs under the outward bending strain is due to larger conductivity of a-Si:H, stemmed from the shift up of Fermi level (E(F)). Experimental results show the I(PLC) of a-Si:H TFTs under the outward bending strain is larger than that of flattened and inward bending a-Si:H TFTs in the density of states (DOS) limited region, stemmed from the lower recombination centers present in outward bending a-Si:H material. Furthermore, the extracted smaller activity energy (E(a)) of a-Si:H TFTs under the outward bending strain also confirmed the shift of E(F). (C) 2010 Elsevier Ltd. All rights reserved.
Mechanical bending effect on the photo leakage currents characteristic of amorphous silicon thin film transistors
(2010-11-01)
Wang, M. C.
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Tsao, S. W.
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Chang, T. C.
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Lin, Y. P.
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Liu, Po-Tsun
The photo leakage current (I(PLC)) characteristic of a-Si:H TFTs under different bending strains has been studied. The larger I(PLC) of a-Si:H TFTs under the outward bending strain is due to larger conductivity of a-Si:H, stemmed from the shift up of Fermi level (E(F)). Experimental results show the I(PLC) of a-Si:H TFTs under the outward bending strain is larger than that of flattened and inward bending a-Si:H TFTs in the density of states (DOS) limited region, stemmed from the lower recombination centers present in outward bending a-Si:H material. Furthermore, the extracted smaller activity energy (E(a)) of a-Si:H TFTs under the outward bending strain also confirmed the shift of E(F). (C) 2010 Elsevier Ltd. All rights reserved.
n(+)-doped-layer-free microcrystalline silicon thin film transistors fabricated with the CuMg as source/drain metal
(2007-07-09)
Wang, M. C.
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Chang, T. C.
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Liu, Po-Tsun
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Xiao, R. W.
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Lin, L. F.
The feasibility of using CuMg as source/drain metal electrodes for n(+)-doped-layer-free microcrystalline silicon thin film transistors (mu-Si:H TFTs) has been investigated. The Ohmic-contact characteristic has been achieved by using the CuMg alloy as source/drain metal. Furthermore, a wet etching process of Cu alloy source/drain metal has been completed by using the ferric chloride base etchant. The proposed mu-Si:H TFT has shown similar electrical characteristic with the mu-Si:H TFT with n(+)-doped layer. The experimental result also showed that the CuMg alloy was suitable for the replacement of n(+)-doped layer in thin film transistor liquid-crystal displays. (C) 2007 American Institute of Physics.
Optical characteristics of a-plane InGaN/GaN multiple quantum wells with different well widths
(2007-04-30)
Ko, T. S.
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Lu, T. C.
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Wang, T. C.
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Lo, M. H.
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Chen, J. R.
a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm were grown on r-plane sapphire by metal organic chemical vapor deposition for investigation. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL study shows that the sample with 3-nm-thick wells has a better optical property with a fast exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify the more uniform and stronger luminescence intensity distribution observed for the samples of thinner quantum wells, indicating that the important growth parameters for a-plane InGaN/GaN multiple quantum wells could be dominated by the In fluctuation and crystal quality during the epitaxial growth. (c) 2007 American Institute of Physics.
Optical study of a-plane InGaN/GaN multiple quantum wells with different well widths grown by metal-organic chemical vapor deposition
(2008-11-01)
Ko, T. S.
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Lu, T. C.
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Wang, T. C.
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Chen, J. R.
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Gao, R. C.
a-plane InGaN/GaN multiple quantum wells of different widths ranging from 3 to 12 nm grown on r-plane sapphire by metal-organic chemical vapor deposition were investigated. The peak emission intensity of the photoluminescence (PL) reveals a decreasing trend as the well width increases from 3 to 12 nm. Low temperature (9 K) time-resolved PL (TRPL) study shows that the sample with 3-nm-thick wells has the best optical property with a fastest exciton decay time of 0.57 ns. The results of cathodoluminescence and micro-PL scanning images for samples of different well widths further verify that the more uniform and stronger luminescence intensity distribution are observed for the samples of thinner quantum wells. In addition, more effective capturing of excitons due to larger localization energy E(loc) and shorter radiative lifetime of localized excitons are observed in thinner well width samples in the temperature dependent TRPL. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3013435]
Photo-leakage-current characteristic of F incorporated hydrogenated amorphous silicon thin film transistor
(2007-05-07)
Wang, M. C.
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Chang, T. C.
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Liu, Po-Tsun
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Tsao, S. W.
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Chen, J. R.
The photo-leakage-current (I-PLC) characteristic of F incorporated a-Si:H thin film transistor (TFT) has been studied. The device activation energy (E-a) of a-Si:H(:F) TFTs is higher than those of typical a-Si:H TFTs, and resulted in the shift down of Fermi level in a-Si:H(:F). Experimental results show that the I-PLC of a-Si:H(:F) TFTs is smaller than that of conventional a-Si:H TFTs in the density of states limited region, stemmed from the higher recombination centers present in a-Si:H(:F) material. However, the higher I-PLC is observed in the hole conduction region, resulted from the larger E-a in the a-Si:H(:F) TFTs. (C) 2007 American Institute of Physics.
Schottky barrier height for the photo leakage current transformation of a-Si : H TFTs
(2007)
Wang, M. C.
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Chang, T. C.
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Liu, Po-Tsun
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Li, Y. Y.
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Xiao, R. W.
For effectively reducing the off-state signal loss resulting from the a-Si: H thin film transistors' (TFTs) photo leakage current, the a-Si: H TFTs with the use of indium tin oxide as source-drain metal have been fabricated for this study. A remarkable transformation in photo leakage current has been observed under the 3300 cd/m(2) cold cathode fluorescent lamp (CCFL) backlight illumination. The source-drain barrier height engineering has been proposed for this study. According to the energy band diagram, the barrier height for hole is estimated to be about 3 eV. As a result, the photogeneration holes blocked in the Schottky barrier could effectively result in the different characteristic of photo leakage current. (c) 2007 The Electrochemical Society.
Source-drain barrier height engineering for suppressing the a-Si : H TFTs photo leakage current
(2007-12-03)
Wang, M. C.
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Chang, T. C.
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Liu, P. T.
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Li, Y. Y.
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Huang, F. S.
For effectively reducing the off-state signal loss resulted from the a-Si:H TFTs photo leakage current, the a-Si:H TFTs with the use of ITO as source-drain metal have been fabricated for this study. Several TFT structures have been fabricated to examine this characteristic. A remarkable reduction in photo leakage current has been observed under the 3300 cd/m(2) CCFL backlight illumination. The source-drain barrier height engineering has been proposed for these results. According to the energy band diagram, the barrier height for hole is estimated about 3 eV. As a result, the photo-generation holes blocked in the source-drain barrier height could effectively reduce the photo leakage current in off-state. (C) 2007 Elsevier B.V. All rights reserved.