Browsing by Author "Wang, Jia-Feng"

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Dark current suppression of amorphous selenium based photosensors by the ZnO hole blocking layer
(2014-05-01)
Yu, Tung-Yuan
;
Pan, Fu-Ming
;
Chang, Cheng-Yi
;
Hu, Tien
;
Chen, Jenn-Fang
To study the influence of defects in the hole blocking layer (HBL) on the dark current of amorphous selenium (a-Se) based photosensors, we prepared ZnO thin films by reactive sputter deposition (RSD) for the use as the HBL of the photosensors. The ZnO HBL layers prepared with different oxygen flow rates were characterized by X-ray photoelectron spectroscopy, Raman scattering analysis and photoluminescence, indicating that the density of oxygen vacancies in the ZnO thin films is significantly affected by the oxygen flow rate. The deep level transient spectroscopy measurement reveals two hole trap levels present in the RSD deposited ZnO thin films; one is at 0.94 eV and the other at 0.24 eV above the valence band edge. The electrical performance of the a-Se photosensor is largely influenced by the amount of oxygen vacancies in the ZnO thin film. The a-Se photosensor with the ZnO HBL of the most oxygen vacancies has the lowest dark current and demonstrates the highest breakdown field. (C) 2014 Elsevier B.V. All rights reserved.
Electron Emission Properties of GaAsN/GaAs Quantum Well Containing N-Related Localized States: The Influence of Illuminance
(2012-02-01)
Hsieh, Meng-Chien
;
Wang, Jia-Feng
;
Wang, Yu-Shou
;
Yang, Cheng-Hong
;
Chiang, Chen-Hao
This study elucidates the electron emission properties of GaAsN/GaAs quantum well containing N-related localized states under illumination. The N-related localized states in a GaAsN quantum well (QW) are identified as both optical and electrical electron trap states. The mechanisms for the responses of current-voltage (I-V) measurement under illumination and photocapacitance are investigated. N-related localized states in GaAsN QW can extend response range and response sensitivity on photocapacitance, and produce an additional current path for photo-generated electron-hole pairs. Furthermore, exactly how illumination influences the electron emission rate of GaAsN QW electron state is examined. The electron emission rate of GaAsN QW electron state can be modulated by different incident photon energy, which is due to the modulation of depletion width of the bottom GaAs. (C) 2012 The Japan Society of Applied Physics
Photoluminescence Study of Interdot Carrier Transfer on Strain-relaxed InAs Quantum Dots
(2011)
Chiang, Chen-Hao
;
Chang, You-Cheng
;
Wu, Yue-Han
;
Hsieh, Meng-Chien
;
Yang, Cheng-Hong
Photoluminescence (PL) properties of the strain relaxed InAs quantum dots (QDs) are studied as a function of temperature from 10 to 300 K. Two groups of QDs induced by strain relaxation are observed in the PL spectra. The PL peak position of the relaxed (non-relaxed) QDs locates at a higher (lower) energy. TEM image prove QDs are distributed into two groups and indicate the QDs relax the strain by diffusing indium to GaAs. In the 120- 200 K temperature range, there are abnormal temperature behaviors attributed to the carrier transfer from the relaxed to non-relaxed QDs.
Role of the N-related localized states in the electron emission properties of a GaAsN quantum well
(2011-11-15)
Hsieh, Meng-Chien
;
Wang, Jia-Feng
;
Wang, Yu-Shou
;
Yang, Cheng-Hong
;
Chen, Ross C. C.
This study elucidates the influence of the N-related localized states on electron emission properties of a GaAsN quantum well (QW) that is grown by molecular beam epitaxy. The N-related localized states in a GaAsN QW are identified as both optical and electrical electron trap states. Furthermore, exactly how N-related localized states influence the electron emission properties of a GaAsN quantum well is examined. The presence of N-related localized states effectively suppresses the tunneling emission of GaAsN QW electron states, leading to a long electron emission time for the GaAsN QW electron states. Thermal annealing can reduce the number of N-related localized states, resulting in a recovery of the tunneling emission for GaAsN QW electron states. Increasing the annealing temperature can restore the electron emission behavior of GaAsN QW to the typical electron tunneling emission for a high-quality QW. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3663436]
Sweeping-rate-dependent photocurrent of GaAs Schottky diode with strain relaxed InAs quantum dots
(2015-04-01)
Wang, Jia-Feng
;
Lin, Cheng-Lu
;
Pan, Sheng-Shiang
;
Huang, Chih-Pin
;
Hsieh, Chao-Sheng
We demonstrate that the photocurrent of a GaAs Schottky diode can be influenced by the carrier stored in strain relaxed InAs quantum dots (QDs) embedded in the Schottky diode. A potential drop is induced by the charged QDs, and the photocurrent generated from the Schottky diode can be suppressed by the induced potential drop. In this paper, the charging time of the relaxed InAs QDs is obtained from 0.1 to 10 s. So the variation in photocurrent can be detected, if the sweeping rate of applied bias is from 10 to 0.1V/s. Two kinds of QD samples, relaxed and non-relaxed InAs QDs, are compared, and we found that the photocurrent is obviously influenced in the relaxed InAs QD sample. A equivalent RC circuit modal also is provided to analyze the formula of the photocurrent, and the analysis agrees with the results of measurements. This study is advantageous for the investigation of QD memory devices. (C) 2015 The Japan Society of Applied Physics