Characterization of charge collection in CdTe and CZT using the transient current technique

The charge collection properties of Cadmium–Telluride (CdTe) and Cadmium–Zinc–Telluride (CZT) in comparison with Silicon (Si) are presented using the transient-current technique (TCT) where the current pulses are generated by αα-particles emitted from an 241Am source. From the recorded current pulse shapes, the charge collection efficiency, the charge carrier mobility and the electric field distribution inside the detectors are extracted. In particular, the signals of the compound semiconductors CdTe and CZT are interpreted with respect to the build-up of space–charges in the sensor volume and the subsequent deformation of the electric field. As high-quality CdTe and CZT samples are now commercially available, the knowledge of these material characteristics is of outmost importance for the application of CdTe and CZT in X-ray imaging.In addition, the paper describes the influence of Ohmic and Schottky contacts on the current pulses in CdTe as well as the effects of polarization, i.e. the time-dependent degradation of the detector signals due to the accumulation of fixed charges within the sensor.