Observations of a deep-donor recharge and its influence on trapping in detector-grade CdZnTe

We report on the recharging of the deep-donor that can drastically decrease the efficiency of charge collection in detector-grade CdZnTe:ln crystals. We used several complementary experimental methods to characterize the material. Photoconductivity mapping was performed using measurements for both the contactless method and with evaporated Au contacts. Measurements of photoconductivity, photoconductivity quenching, surface photo voltage and thermoelectric effect spectroscopy revealed a rechargeable energy level at E_c-0.65 eV. Photoluminescence measurements identified this level as responsible for the 0.68-e V emission. Its neutral charge can be converted into a positive one by the downward displacement of the Fermi level, thus increasing the trapping of photoelectrons. Our research attributed this near middle-gap donor level to a tellurium antisite, TeCd or Te vacancy. This report demonstrates that even in some carefully grown samples of CdZnTe, unintentional impurities, mainly alkali metals or Te precipitates, can shift the Fermi level thus influencing carrier trapping.