Deep-Level Defect Effects on the Low-Temperature Photoexcitation Process in CdZnTe Crystals

The low-temperature photoexcitation process in Cd_0.9Zn_0.1Te:In crystals was investigated. Generation-recombination-trapping processes through deep-level defects approach the relative balance, thus forming the photoexcitation transients and demonstrating the carrier transport properties. The carrier transport properties controlled by deep-level defects and reflected in the photoexcitation transients have been experimentally investigated by the analysis of the thermally stimulated current (TSC) spectra. The time-dependent photoconductivity buildup process could be interpreted as resulting from the four independent photoexcitation processes of the four trap levels identified in TSC spectra. The buildup curve could be modeled by a multi-exponential function, consisting of the four capture rates describing the four photoexcitation processes. Each photoexcitation process is fitted by a mono-exponential function and the capture rate is obtained initially for the deep trap and followed by shallow traps, by combining photoconductivity and TSC measurements, with illumination time ranging from 10 s to 100 s. The photoexcitation of electrons at the shallow donor originating at In dopant related point defects could be considered the main origin of the photoconductivity buildup process in CdZnTe crystals at low temperature. Understanding the photoexcitation process provides valuable information on the mechanisms for carrier storage, relaxation and transport properties, which is of great importance for fundamental physics and device applications.