Stability of X-Ray Irradiated Amorphous Selenium Based Photoconductive Films

Abstract

Amorphous selenium (a-Se) is a photoconductive material that is used in commercial x-ray imaging flat panels. In this study, the effect of x-ray irradiation on the glass stability of aged vitreous a-Se, a-Se:0.5%As, a-Se:6%As-140 ppm Cs thin films are investigated by using differential scanning calorimetry (DSC). This technique is used to detect characteristic temperatures, such as glass transition, crystallization and melting temperatures of the material in terms of the change in the heat flow in a certain temperature scanning range. To investigate glass stability of a-Se based alloy films, fourteen different glass stability criteria are examined. Initially, the reproducibility of stability criteria is analyzed for unirradiated samples, which also provides confidence in the variation of the characteristic temperatures. The study consists of three main stages of glass stability investigation. In the first stage, the a-Se based alloy film samples are dosed with x-rays at different periods and scanned in DSC afterwards. In the second stage, x-ray irradiated samples are rested for an arbitrary period of five hours at laboratory ambient temperature of 295 K. Further, the effect of five hour-annealing on x-ray irradiated samples is analyzed at annealing temperatures of 308 K and 328 K. In the third stage, various annealing periods are inspected for equally x-ray irradiated films that are rested at 308 K and 328 K. Results show that under high x-ray irradiation, the characteristic onset temperatures of a-Se based alloy films have not shown significant instability. On the other hand, least stable case was obtained for the films rested at 328 K after irradiation. The investigation on various resting periods of equally irradiated samples showed that higher stability was achieved at 308 K. In addition, ΔTxg, KH and KW were found to be the most useful criteria in analyzing the stability of a-Se based alloy films.