AbstractID: 8246 Title: Mechanism of sensitivity reduction in a-Se flat panel imagers
A theoretical model describing the process of sensitivity reduction responsible for latent images (or ghosting) commonly seen in
amorphous selenium active matrix flat panel imagers (AMFPIs) due to x-ray irradiation has been developed. After an AMFPI is
irradiated and an image is acquired, its sensitivity decreases. The result is a latent or “ghost” image which is visible in subsequent
acquired images; a particular problem in fluoroscopic imaging. In addition to ghosting, there is an increase in the signal collection lag
time associated with the detector as well. The origin of this ghosting and increased lag is due to charge trapping in deep localized
states of the a-Se material. Differential equations incorporating carrier photogeneration, trapping, and recombination have been used
to derive a semi-analytical expression for a biased photoconductor configuration to describe the temporal AMFPI detector sensitivity
response. In addition, sensitivity reduction dependencies for varying detector thickness, dose rates, incident x-ray energies, density of
traps, and applied electric fields have been investigated. Experimental data can be used in conjunction with these theoretical models to
characterize the trapping intensities of excited holes (g0p), and electrons (g0n). By implementing these values for g0p and g0n , a variety
of different AMFPI detector parameters can be chosen, and accurate temporal sensitivity response can be generated.