Improvement of temporal response and output uniformity of polycrystalline CdZnTe films for high-sensitivity x-ray imaging

Abstract

X-ray detectors that we developed utilizing polycrystalline CdZnTe films exhibited superior sensitivity, but inadequate temporal response and output uniformity for medical imaging purposes. In order to improve those deficiencies, we tested new procedures for deposition and post-deposition chemical-heat treatment of polycrystalline CdZnTe films, in addition to investigating new device structures. We doped the polycrystalline CdZnTe films with Cl in a new manner so as to achieve effective grain boundary passivation. Polycrystalline CdZnTe films that were Cl-doped by our new procedure were found to have a finer and more uniform grain structure. We fabricated and evaluated devices with a replaced barrier layer against charge injection under negative bias. All these measures helped reduce the temporal lag of a 300 μm thick polycrystalline CdZnTe film exposed to X-ray irradiation. Moreover, utilizing this film in a detector reduced the detector's output uniformity. We have succeeded in improving the X-ray temporal response and output uniformity of a 300 μm thick CdZnTe film. This study will also discuss countermeasures against a number of problems that were encountered, including MTF degradation and short range image lag.