Abstract-Te inclusions existing at high concentrations in CdZnTe (CZT) material can degrade the performance of CZT detectors. These microscopic defects trap the free electrons generated by incident radiation, so entailing significant fluctuations in the total collected charge and thereby strongly affecting the energy resolution of thick (long-drift) detectors. Such effects were demonstrated in thin planar detectors, and, in many cases, they proved to be the dominant cause of the low performance of thick detectors, wherein the fluctuations in the charge losses accumulate along the charge's drift path. We continued studying this effect using different tools and techniques. We employed a dedicated beam-line recently established at BNL's National Synchrotron Light Source for characterizing semiconductor radiation detectors, along with an IR transmission microscope system, the combination of which allowed us to correlate the concentration of defects with the devices' performances. We present here our new results from testing over 50 CZT samples grown by different techniques. Our goals are to establish tolerable limits on the size and concentrations of these detrimental Te inclusions in CZT material, and to provide feedback to crystal growers to reduce their numbers in the material.

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The Cr 2ϩ doped CdS 0.8 Se 0.2 crystals were grown by the vertical, self-seeded, physical vapor transport (PVT) technique. Good quality, crack-and inclusionfree single crystals were grown with an average Cr 2ϩ concentration of 5 ϫ 10 18 cm Ϫ3 . Different source-to-tip distances were used to improve the segregation coefficient (Cr crystal /Cr source ) of the grown crystals. It was observed that lowering the source-to-tip distance increases the segregation coefficient dramatically. With a 2-cm source-to-tip distance, good quality crystals were grown with uniform Cr 2ϩ concentration throughout the ingot. The segregation coefficient was found to be ϳ0.85. The composition of the crystals was also found to be fairly uniform along the length and across the diameter.