Browsing by Author "Lin, Jian-Siang"

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Effect of hole blocking dielectric layer on microstructure and photoconducting properties of polycrystalline Se thin films
(2018-09-01)
Chang, Cheng-Yi
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Lin, Yi-Jie
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Huang, Yu-Wei
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Liao, Jye-Yow
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Lin, Jian-Siang
We fabricated polycrystalline selenium (c-Se) based photodetectors using three different dielectrics (HfO2, Al2O3 and SiO2) as the hole blocking layer (HBL), and studied the influence of the HBLs on the photoconducting performance of the photodetectors. The microstructure of the c-Se layer is greatly influenced by the nucleation behavior of the tellurium (Te) adhesion layer deposited between the c-Se layer and the HBLs. The photoconducting performance of the photodetectors is basically dependent on the barrier height at the junctions of the HBL with the tin-doped indium oxide (ITO) anode and with the c-Se layer. A higher barrier height at the HBL/ITO junction leads to a lower dark current density (I-D) of the photodetectors. However, the photodetector with the SiO2 HBL exhibits the largest I-D as the bias exceeds 2 V although it has the highest junction barrier height. We attribute the abnormity to the rugged morphology of the c-Se layer, which is a result of a less dense Te nucleation on the SiO2 HBL. The photocurrent density (I-ph) is inversely related to the junction barrier height at the HBL/c-Se contact. The c-Se photodetector with the HfO2 HBL has the largest I-Ph and the one with the SiO2 HBL has the smallest. The photodetector with the HfO2 HBL exhibits a quantum efficiency of 89% at 6 V.
Lateral amorphous selenium metal-insulator-semiconductor-insulator-metal photodetectors using ultrathin dielectric blocking layers for dark current suppression
(2016-12-21)
Chang, Cheng-Yi
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Pan, Fu-Ming
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Lin, Jian-Siang
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Yu, Tung-Yuan
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Li, Yi-Ming
We fabricated amorphous selenium (a-Se) photodetectors with a lateral metal-insulator-semiconductor-insulator-metal (MISIM) device structure. Thermal aluminum oxide, plasma-enhanced chemical vapor deposited silicon nitride, and thermal atomic layer deposited (ALD) aluminum oxide and hafnium oxide (ALD-HfO2) were used as the electron and hole blocking layers of the MISIM photodetectors for dark current suppression. A reduction in the dark current by three orders of magnitude can be achieved at electric fields between 10 and 30 V/mu m. The effective dark current suppression is primarily ascribed to electric field lowering in the dielectric layers as a result of charge trapping in deep levels. Photogenerated carriers in the a-Se layer can be transported across the blocking layers to the Al electrodes via Fowler-Nordheim tunneling because a high electric field develops in the ultrathin dielectric layers under illumination. Since the a-Se MISIM photodetectors have a very low dark current without significant degradation in the photoresponse, the signal contrast is greatly improved. The MISIM photodetector with the ALD-HfO2 blocking layer has an optimal signal contrast more than 500 times the contrast of the photodetector without a blocking layer at 15 V/mu m. Published by AIP Publishing.
Photoconductive properties of polycrystalline selenium based lateral MISIM photodetectors of high quantum efficiency using different dielectrics as the charge blocking layer
(2019-07-01)
Chang, Cheng-Yi
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Huang, Yu-Wei
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Lin, Yi-Jie
;
Liao, Jye-Yow
;
Lin, Jian-Siang
We studied the photoconductive performance of polycrystalline selenium (pc-Se) based photodetectors with a lateral metal-insulator-semiconductor-insulator-metal (MISIM) device structure. The insulator layer is a 10 nm-thick Ga2O3, HfO2, or Al2O3 thin film, and used as a charge blocking layer (CBL) to suppress dark current injected from the Al electrodes. The dark current suppression primarily depends on the barrier height of the junctions between the CBLs and electrodes. The Ga2O3 CBL exhibits a poor dark current suppression compared to the HfO2 and the Al2O3 CBLs because of a lower electron barrier at the cathode. The lateral pc-Se photodetectors exhibit a very high internal photocurrent gain due to Fowler-Nordheim tunneling at relatively low applied voltages. The better crystallinity of pc-Se grains formed on the Ga2O3 CBL leads to a higher photoconversion efficiency for the MISIM-Ga2O3 photodetector. Compared with amorphous Se based lateral MISIM photodetectors, the pc-Se photodetectors demonstrate a uniform and much better photoconductive performance over the visible spectrum.
Thermal stability and photoconductive properties of photosensors with an alternating multilayer structure of amorphous Se and AsxSe1-x
(2015-07-28)
Yu, Tung-Yuan
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Pan, Fu-Ming
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Chang, Cheng-Yi
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Lin, Jian-Siang
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Huang, Wen-Hsien
In this study, we fabricated a-Se based photosensors with an alternating multilayer structure of a-Se and AsxSe1-x by rotational thermal evaporation deposition. During the deposition of the amorphous AsxSe1-x layers, As diffuses into the underlying a-Se component layers, thereby improving the thermal stability of the multilayer photosensor and thus increasing the breakdown electric field. Although the As doping introduces carrier traps in the a-Se layers, the multilayer photosensors demonstrate an effective quantum efficiency comparable to the single-layered a-Se sensor under the blue light illumination but are with a lower dark current density by two orders of magnitude. In addition to the top AsxSe1-x layer being functioning as an electron blocking layer, carrier traps present in the multilayer structure may decrease the drift mobility of charge carriers and disturb electric field distribution in the photosensors, thereby suppressing the dark current. (C) 2015 AIP Publishing LLC.