Influence of impurities and structural defects on electrophysical and detector properties of CdTe and CdZnTe

Abstract

Solid-state ionizing radiation detectors based on high-resistance semiconductors can be used to monitor the safety of nuclear reactors. High-resistance CdTe and CdZnTe have very good electrophysical and detector properties. The objective of this study was to use computer simulation to determine how impurities and structural defects, as well as their clusters, affect electrophysical and detector properties of Cd1-xZnxTe (0≤x≤0.3). The calculations were based on well-tested models, the reliability of which was confirmed when comparing simulation results with well-known experimental data. It has been established that deep donors with energy levels near the middle of the band gap considerably extend the area of the high-resistance state of CdTe and CdZnTe, which is suitable for the creation of radiation detectors. The capture and recombination of non-equilibrium charge carriers occurs at the deep levels of cadmium vacancies owing to the influence of Ti, V, Ge, Ni, and Sn impurities. For this reason, such impurities are considered to be harmful, noticeably reducing the efficiency of charge collection η in CdTe and CdZnTe detectors. The decrease of electron mobility in CdTe and CdZnTe can be caused by the distribution heterogeneity of impurities (impurity clusters).When concentration of harmful impurities Ti, V, Ni, Sn, Ge does not exceed the content of the "background", provided that the impurities are distributed over the crystal uniformly, it is possible to obtain high-resistance CdZnTe of an acceptable detector quality. The obtained results could help determining conditions for producing CdTe and CdZnTe materials of high detector quality.