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Proceedings Paper

Ghosting mechanisms in a-Se based direct conversion x-ray image sensors
Author(s): M. Zahangir Kabir; M. Yunus; S. O. Kasap; Olivier Tousignant; Habib Mani; Philippe Gauthier
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Paper Abstract

The dependence of the x-ray sensitivity of a-Se based x-ray image detectors on repeated x-ray exposures is studied by considering deep trapping of charge carriers, trapped charges due to previous exposures, trap filling effects, recombination between trapped and drifting carriers, x-ray induced new deep trap center generation, space charge effects, and electric field dependent electron-hole pair creation energy. We simultaneously solve the continuity equations for both holes and electrons, trapping rate equations, and the Poisson’s equation across the photoconductor for a pulse x-ray exposure by the finite difference method. We also perform Monte Carlo Simulations of carrier transports and obtain almost identical results. The change in relative sensitivity (ghosting) as a function of cumulative x-ray exposures for different levels of trapping and different detector operating conditions are examined. The relative sensitivity decreases with increasing cumulated x-ray exposure. The amount of ghosting in a-Se detectors increases with decreasing applied electric field. The sensitivity reduction at negative bias is greater than at positive bias. The theoretical model shows a very good agreement with the experimental relative sensitivity vs. cumulative x-ray exposure characteristics. The comparison of the model with the experimental data reveals that the recombination between trapped and the oppositely charged drifting carriers and x-ray induced new deep trap centers are mainly responsible for the sensitivity reduction in biased a-Se-based x-ray detectors.

Paper Details

Date Published: 20 April 2005
PDF: 9 pages
Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005); doi: 10.1117/12.594692
Show Author Affiliations
M. Zahangir Kabir, Univ. of Saskatchewan (Canada)
M. Yunus, Univ. of Saskatchewan (Canada)
S. O. Kasap, Univ. of Saskatchewan (Canada)
Olivier Tousignant, Anrad Corp. (Canada)
Habib Mani, Anrad Corp. (Canada)
Philippe Gauthier, Anrad Corp. (Canada)

Published in SPIE Proceedings Vol. 5745:
Medical Imaging 2005: Physics of Medical Imaging
Michael J. Flynn, Editor(s)

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