Characterization of CZT crystals grown by the Boron Oxide Encapsulated Vertical Bridgman technique for the preparation of X-ray imaging detectors"

Abstract

CdZnTe crystals are employed for the preparation of X- and Gamma- ray detectors. However, the large-scale production of these detectors is limited by the low yield of material with the required material properties, i. e. high resistivity, high carrier mobility lifetime product, and low inclusion density. In this frame, a new technique for the growth of CZT crystals has been developed based on a modification of the vertical Bridgman technique consisting in the encapsulation of the molten charge by a layer of boron oxide [1]. The authors have found that due to a chemical interaction with the quartz ampoule [2], a boron oxide layer fully encapsulates the crystal during growth preventing the direct contact of the crystal and the crucible walls. As a consequence, 2-inches CZT crystals characterized by large single grains and extremely low dislocations density have been grown. More recently, x-ray detectors with spectroscopic characteristics and good mobility lifetime product have been obtained using these crystals [3]. In this work we present an extensive characterization of these crystals with different techniques, ranging from energy dispersion x-ray analysis, photoluminescence mapping, contactless resistivity mapping, and infrared transmission. As a result, it is determined the interface shape and the zinc concentration distribution, that is related to the fluido-dynamic properties of the melt during growth. Moreover, the good homogeneity of resistivity is demonstrated. Finally, the typical inclusion density of these crystals is studied, hence the possibility to use them for the preparation of imaging and high flux x-ray detectors