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Proceedings Paper

Electrical interface characteristics (I-V), optical time of flight measurements, and the x-ray (20 keV) signal response of amorphous-selenium/crystalline-silicon heterojunction structures
Author(s): David M. Hunter; Chu An Ho; George Belev; Giovanni De Crescenzo; Safa O Kasap; Martin J. Yaffe
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Paper Abstract

We have investigated the dark current, optical TOF (time of flight) properties, and the X-ray response of amorphousselenium (a-Se)/crystalline-silicon (c-Si) heterostructures for application in digital radiography. The structures have been studied to determine if an x-ray generated electron signal, created in an a-Se layer, could be directly transferred to a c-Si based readout device such as a back-thinned CCD (charge coupled device). A simple first order band-theory of the structure indicates that x-ray generated electrons should transfer from the a-Se to the c-Si, while hole transfer from p-doped c-Si to the a-Se should be blocked, permitting a low dark signal as required. The structures we have tested have a thin metal bias electrode on the x-ray facing side of the a-Se which is deposited on the c-Si substrate. The heterostructures made with pure a-Se deposited on epitaxial p-doped (5×10 14 cm-3) c-Si exhibited very low dark current of 15 pA cm-2 at a negative bias field of 10 V μm-1 applied to the a-Se. The optical TOF (time of flight) measurements show that the applied bias drops almost entirely across the a-Se layer and that the a-Se hole and electron mobilities are within the range of commonly accepted values. The x-ray signal measurements demonstrate the structure has the expected x-ray quantum efficiency. We have made a back-thinned CCD coated with a-Se and although most areas of the device show a poor x-ray response, it does contain small regions which do work properly with the expected x-ray sensitivity. Improved understanding of the a-Se/c-Si interface and preparation methods should lead to properly functioning devices.

Paper Details

Date Published: 17 March 2011
PDF: 11 pages
Proc. SPIE 7961, Medical Imaging 2011: Physics of Medical Imaging, 79610X (17 March 2011); doi: 10.1117/12.877738
Show Author Affiliations
David M. Hunter, Sunnybrook Health Sciences Ctr. (Canada)
Chu An Ho, Sunnybrook Health Sciences Ctr. (Canada)
George Belev, Univ. of Saskatchewan (Canada)
Giovanni De Crescenzo, Thunder Bay Regional Research Institute (Canada)
Safa O Kasap, Univ. of Saskatchewan (Canada)
Martin J. Yaffe, Sunnybrook Health Sciences Ctr. (Canada)
Univ. of Toronto (Canada)

Published in SPIE Proceedings Vol. 7961:
Medical Imaging 2011: Physics of Medical Imaging
Norbert J. Pelc; Ehsan Samei; Robert M. Nishikawa, Editor(s)

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