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Investigation of Hole-Blocking Contacts for High-Conversion-Gain Amorphous Selenium Detectors for X-Ray Imaging

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5 Author(s)
Abbaszadeh, S. ; Electrical and Computer Engineering Department, University of Waterloo, Waterloo, Canada ; Allec, N. ; Ghanbarzadeh, S. ; Shafique, U.
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In this paper, we investigated different organic and inorganic hole-blocking contacts for amorphous selenium (a-Se)-based photodetectors: \hbox {CeO}_{2} , \hbox {TiO}_{2} , perylene tetracarboxylic bisbenzimidazole (PTCBI), and polyimide (PI). \hbox {CeO}_{2} has previously been used as a blocking layer for high-gain a-Se devices. \hbox {TiO}_{2} has similar properties to \hbox {CeO}_{2} . PTCBI has a higher ionization potential compared to a-Se and has a very low hole mobility. PI is a common insulator in the semiconductor industry. It was found that an 800-nm PI layer reduces the dark current by more than two orders of magnitude in comparison with 30 nm of \hbox {CeO}_{2} , 20 nm of \hbox {TiO}_{2} , and 50 nm of PTCBI. No significant charge trapping was found in the devices consisting of an 800-nm PI layer. Unlike previously reported inorganic hole-blocking contact technology, PI layers further benefit from a simple spin coating fabrication step before evaporation of a-Se. Photodetector samples incorporating the PI layer are tested at high electric fields, and gains reaching 4.4 were observed at an electric field >\hbox {80} \hbox {V}/\mu \hbox {m} . We conclude that using a PI layer is a promising step in the development of high-conversion-gain detectors for emerging applications in large-area medical diagnostic imaging, crystallography, and nondestructive test.

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Electron Devices, IEEE Transactions on  (Volume:59 ,  Issue: 9 )