X-ray induced effects in stabilized a-Se X-ray photoconductors

We report on X-ray induced changes in the electrical properties of stabilized amorphous selenium typical of the material used in direct conversion X-ray imaging devices. Carrier mobility and deep-trapping lifetime were measured using time-of-flight and interrupted-field time-of-flight (IFTOF) measurements. The hole and electron drift mobility is not affected by up to 1 R of exposure to 50 kVp X-rays. The hole lifetime decreases from 50 to 27 μs after exposure to 0.48 R. The hole lifetime slowly recovers to its initial value after circa 3000 min. The electron lifetime does not change after exposure to 1 R. The results are explained by an accumulation of excess hole traps due to capture of electrons in deep localized states. We also observe small changes in the dark current after exposure to X-rays.