Optical characterization of the internal electric field distribution under bias of CdZnTe radiation detectors

Polarized transmission optical profiles were used to characterize the CdZnTe (CZT) room-temperature radiation detectors, The internal electric field distributions of the CZT detectors under bias were probed by a 952 nm illumination between two crossed Glan-Taylor polarizers. A 16-bit digital charge coupled device (CCD) was employed as an image sensor. The 2-dimensional (2D) images reflecting the internal electrical field intensity changes were obtained utilizing the Pockels electro-optic effect. CZT detectors of crystal sizes of 5x5x5 mm were investigated under different bias voltages. Uniform and non uniform internal electric field distributions throughout the detector volumes, under different light illumination conditions, were observed and analyzed. A theoretical model or the semiconductor energy band structure under the bias was established and used to understand the measurement results.