Investigating the Components of Signals Produced by the Pockels CCD Imaging Technique in CdZnTe

Abstract

Several groups have demonstrated the potential of the Pockels effect in cadmium zinc telluride as a means to detect ionizing radiation. Migrating charge carriers are believed to generate the signal detected via the Pockels effect due to the distortions they create within the electric field; however, trapped space charge beneath the cathode has been regularly observed, which suggests field changes away from the charge generation area. Consequently, the Pockels signal amplitude contains a charge integrated, i.e., dose element. In this paper, the effects of electric field collapse at the location of charge carrier generation are demonstrated. This opens the potential to apply the technique for imaging dose rate distributions. Charge-coupled device images representing the changes in an electric field within the crystal were taken, and the response to illumination from a collimated 1550-nm, 4.5-mW IR laser and irradiation from 150-kVp X-rays was measured. The data demonstrate that the signal acquired is a combination of both the local change in the electric field at the location where the carriers are being released/generated and an element caused by carriers becoming trapped, leading to electric field enhancement due to space charge near the cathode and field reduction toward the anode.