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.