Correlation between nuclear response and defects in CZT

Abstract

Vertical high pressure Bridgman (VHPB) was considered until now to be the most successful crystal growth method to produce CZT, for x- and gamma-ray detector crystals. Recently horizontal Bridgman (HB) CZT crystals produced by IMARAD Co. have also been successfully fabricated into nuclear spectroscopic radiation detectors. In view of our database of many years' study of the electrical properties of VHPB CZT grown and obtained from various sources we also studied the HB CZT crystals in order to compare the defects present in both different kinds of crystals grown by different methods. The VHB-grown samples were examined using thermoelectric emission spectroscopy (TEES), x- and gamma- ray spectroscopy and laser induced transient charge technique (TCT). The surface and the bulk crystalline homogeneity were mapped using triaxial double crystal x-ray diffraction and IR transmission spectroscopy. We have found a correlation between crystallinity, IR transmission microstructure an trapping times. Spectrometer grade VHPB CZT crystal exhibit trapping times of 20 microsecond(s) for electrons and 7 microsecond(s) for holes, however, regions, which were opaque to IR transmission, had trapping times shorter by one order of magnitude. The trapping times of HB CZT for electrons, were 10-15 micrometers . A similar trend has been observed on VHPB CZT crystals with poor crystallinity. The HB CZT crystals that we measured in this study had a crystallinity that was inferior to that of the best spectroscopic grade VHPB crystals.