Physics MSc Thesis Defense Presented By Tristen T. Thibault

^Abstract:
The reduction of the dark current (DC) to a tolerable level in X-ray photoconductors is one of the key factors for their application as X-ray-to-charge transducers in the direct conversion flat panel X-ray imagers (FPXIs). Here, we discuss the origins of DC in an X-ray-to-charge transducer that is based on one of the most promising X-ray photoconductors: amorphous lead oxide (a-PbO). The transient DC in an a-PbO blocking structure is measured at different applied electric fields (5–20 V/μm). The experimental results are used to develop a theoretical model describing the electric field-dependent transient behavior of DC. We show that DC decay is caused by charge accumulation in deep localized states (traps) within the blocking layer. Accounting for the field-induced charge carrier release from traps, enhanced by charge hopping transitions, yields an excellent fit between the experimental and simulated results, thus clarifying the dynamic process of reaching a steady-state occupancy level of the deep localized states in the blocking layer. The model can be used to find an approximate optimal thickness of blocking layers for future iterations of a-PbO – based detectors without the need for time and labor-intensive experimental trial and error.