Charge carrier transport mechanisms in CdZnTe detectors grown by the vertical Bridgman technique

In this work, we report on the results of electrical characterization of CdZnTe (CZT) detectors, with gold electroless contacts, grown by the boron oxide encapsulated vertical Bridgman technique (B-VB), currently produced at IMEM-CNR (Parma, Italy). The detectors, with different thicknesses (1 and 2.5 mm), have the same electrode layout: the anode is a central electrode (2 × 2 mm2) surrounded by a guard-ring electrode. The cathode is a planar electrode covering the detector surface (4.1 × 4.1 mm2). Current-voltage (I-V) characteristics were measured at different temperatures in order to study the charge transport and the electrical properties. These detectors were compared with the traveling heater method (THM) CdZnTe grown detectors (Redlen, Canada), fabricated with the same electrode layout and deposition. The results highlight the low leakage currents of the B-VB CdZnTe detectors even at high bias voltages: 38 nA/cm2 (T = 25°C) at 10000 V/cm. This feature allows high bias voltage operation, very important for high flux applications. These activities are in the framework of an Italian research project on the development of energy-resolved photon counting (ERPC) systems for high flux energy-resolved X-ray imaging.