Sensitivity reduction mechanisms in amorphous selenium photoconductive x-ray image detectors

Sensitivity reduction in amorphous Se-based photoconductive x-ray image detectors due to previous exposures is studied by Monte Carlo simulation. Collected charge, hence x-ray sensitivity, is calculated by considering deep carrier trapping, taking into account the effects of trap filling, recombination between trapped and drifting carriers and the generation of x-ray induced new deep trap centers. Space charge effects on the electric field, and hence, the effects of electric field on electron hole pair generation and charge transport are also considered. The comparison of the model with the experimental data reveals that the recombination between trapped and 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.

[1]  John A. Rowlands,et al.  Measurement of x-ray photogeneration in amorphous selenium , 1999 .

[2]  Safa Kasap,et al.  Direct-conversion flat-panel X-ray image sensors for digital radiography , 2002, Proceedings of the IEEE.

[3]  M. Abkowitz,et al.  Photoenhanced metastable deep trapping in amorphous chalcogenides near room temperature , 1983 .

[4]  R. Street.  Recombination in amorphous semiconductors , 1978 .

[6]  Robert A. Street,et al.  Photoinduced Defects in Chalcogenide Glasses , 1980 .

[7]  Martin Choquette,et al.  Direct selenium x-ray detector for fluoroscopy, R&F, and radiography , 2000, Medical Imaging.

[8]  Safa Kasap,et al.  Charge collection and absorption-limited sensitivity of x-ray photoconductors: Applications to a-Se and HgI2 , 2002 .

[9]  M. Z. Kabir,et al.  Recombination of drifting holes with trapped electrons in stabilized a-Se photoconductors: Langevin recombination , 2004 .

[10]  Monte Carlo simulations of x-ray induced recombination in amorphous selenium , 2000 .

[11]  Safa Kasap,et al.  X-ray sensitivity of photoconductors: application to stabilized a-Se , 2000 .

[12]  Denny L. Y. Lee,et al.  New digital detector for projection radiography , 1995, Medical Imaging.

[13]  A. Kolobov,et al.  Structural study of amorphous selenium by in situ EXAFS: Observation of photoinduced bond alternation , 1997 .

[14]  John A. Rowlands,et al.  Investigation of lag and ghosting in amorphous selenium flat-panel x-ray detectors , 2002, SPIE Medical Imaging.

[15]  Safa Kasap,et al.  Dependence of x-ray sensitivity of direct conversion x-ray detectors on x-ray exposure and exposure history , 2004, SPIE Medical Imaging.

[16]  Kanai S. Shah,et al.  Comparison of PbI2 and HgI2 for direct detection active matrix x-ray image sensors , 2002 .