Correlation between quality of CZT crystals and spectrometric performance of hemispherical radiation detectors

The work presents analysis of the correlation existing between the spectrometric performance of commercially produced hemispherical detectors of volume 500 mm³ and the quality of starting CdZnTe material. More then 100 detectors made from CdZnTe crystals grown by eV Products, Saint-Gobain and Vinnel Tech. were studied. For the incoming inspection of the material an infrared (IR) transmission microscope was used. The presence of structural defects such as grain boundaries, twins, inclusions and cavities was checked and their shapes, sizes and spatial distributions were examined; the values of electron mobility-lifetime product (mutau)_e were measured. The hemispherical detectors were made by a technology elaborated at the RITEC. Spectrometric performance of the detectors was verified by measuring the energy resolution and the peak-to-Compton ratio at the 662 keV line. It was found that all tested detectors had numerous structure defects, whose shapes, sizes, numbers and spatial distributions varied from sample to sample. Were found that hemispherical detectors made from samples containing inclusions of irregular shape had a poor spectrometric performance, while the detectors from samples containing large inclusions (>50 mum) of regular shape (triangular, hexagonal) as a rule performed well. It was also found that a highly non-uniform spatial distribution of structural defects usually leads to a poor spectrometric performance