Characterization of CZT materials for x-ray and gamma-ray detectors

Cadmium Zinc Telluride (CZT) detectors possess a unique combination of the necessary material properties required for high photon detection efficiency, high resistivity, good photoconductivity and acceptable electrical transport properties, and a great of progress has been made to fabricate good spectroscopic grade detectors from the crystals. Despite these notable advantages, their widespread deployment remains limited due to material defects and to issues associated with manufacturing of the devices. Material defects, such as twins, grain boundaries, Te inclusions, and dislocations are routinely observed in these crystals, which are known to degrade the device performance. We explored and analyzed the defects in various CZT detector-grade materials revealed by different methods, including IR microscopy, chemical etching and high-spatial x-ray mapping. We correlated these data with the findings to disclose the characteristics of the defects. Besides materials issues, imperfection in processed crystals´ surfaces like mechanical damage and chemical species formation influence the electric field within the device, and significantly affect its charge transport characteristics. Such surfaces enhance leakage current into the medium and create additional trapping centers, thereby adversely affecting the detector´s performance. We prepared and processed the surfaces of some selected crystals and studied these treated surfaces by atomic force microscopy to identify the most efficient means of surface processing to yield the optimum quality surface for fabricating radiation detectors.