Various types of Cd1ZnTe (0.04 < x < 0.24) detector crystals grown by vertical high pressure Bridgman (VHPB), low pressure Bridgman (LPB) i.e. vertical ambient pressure Bridgman (YB), horizontal ambient pressure Bridgman (HB) and vapor grown crystals have been evaluated and compared. We have used the following methods in order to evaluate the CZT: 1) Triaxial crystal x-ray diffraction (TAD) for determination of the surface crystalline homogeneity, 2) Nuclear spectroscopic response of detectors and 3) Sensitivity to radiation from high flux x-rays for investigations of the suitability for x-ray digital imaging. Finally a comparison between the various methods of CZT crystal growth will be given.
The n-type conduction of CdTe and Cd096Zn004Te crystals grown from melts with excess tellurium indicates that the origin of the donors with an energy level at 0.01 eV below the conduction band are most likely singly ionized tellurium antisites instead of cadmium interstitials. Based on this model, the deep level at 0.75 eV below the conduction band is therefore doubly ionized tellurium antisites. After increasing the zinc content over 7%, CdZnTe turns to p-type. The conduction type variation of CdZnTe crystals as a ftinction of zinc contents is explained by the compensation between the donors of Te-antisites and the acceptors of Cd vacancies. High resistivity Cd09Zn01Te crystals are produced by compensating the p-type crystals with indium at a low doping level of l-5x10'5 cm3. At room temperature, the high yield CdZnTe radiation detectors can resolve the six low energy peaks from the 241 source, a performance comparable to the best reported CdZnTe detectors.
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