Influence of impurities and structural defects on the properties of CdTe- and CdZnTe-based detectors

Abstract

The most researched materials for uncooled semiconductor detectors of ionizing radiation are CdTe:Cl and Cd0.9Zn0.1Te, which allow to obtain detectors with high values of resistivity ρ and electron mobility. In the process of producing detector materials, the background impurities and defects can be introduced into their matrix, and as a result the deep levels appear in the bandgap, acting as centers of capture and recombination of nonequilibrium charge carriers and reducing the registration ability of detectors. The aim of this study was to determine by computer simulation method the nature of the effect of background impurities and structural defects on the electrophysical and detector properties of CdTe and CdZnTe. Quantitative studies were conducted using reliability-tested models. The authors used the examples of Cl, Fe, Pb, Cr, Co, Ti, V, Ni, Ge, Sn to study the effect of doping and background impurities on the resistivity ρ, lifetime of nonequilibrium electrons and holes, the charge collection efficiency η of detectors based on CdTe and Cd0.9Zn0.1Te. The influence of cadmium vacancies on the degradation of the ρ and η of the detectors based on the materials under study was clarified. Impurities were found that reduce ρ and η in detectors based on CdTe:Cl and Cd0.9Zn0.1Te:Al. The ultimate concentration of donor impurities and defects with their uniform distribution over the crystal volume without the formation of clusters was determined. The effect of the Fermi level and defect levels on the change and degradation of the properties of the materials under study was found. The ratios of the concentrations of background impurities and defects were established, making it possible to obtain semiconductors CdTe:Cl and Cd0.9Zn0.1Te of an acceptable detector quality.