Effects of the Distribution of Secondary-Phase and Deep-Level Defects on the Performance of CdZnTe Nuclear Radiation Detectors

The susceptibility of CdZnTe (CZT) crystals to complex defects during the growth process poses significant challenges in preparing probe-grade CZT single crystals, thereby constraining their extensive application in nuclear radiation detectors. To deeply understand the influence of defects on the performance of CZT crystals, this study systematically investigates the influence of the secondary-phase and related deep-level defect distribution on the photoelectric performance of CZT crystals grown by the vertical gradient freeze (VGF) method. It was found that the crystals with low density of secondary-phase defects and a small defect size have a larger bulk resistivity of 5.13 × 10¹⁰ Ω cm, Hall mobility of 330 cm² . V ^-1 . s⁻¹, and carrier mobility-lifetime product of 1.38 × 10⁻³cm²· V⁻¹. The current deep-level transient spectroscopy (I-DLTS) results indicate that secondary-phase defects of large size and high density contribute to an increased capture cross section of deep-level traps and elevated defect concentrations, respectively. During carrier transport, the secondary phase, Te_i, and [Te_Cd]²⁺-related deep-level defects exhibit prolonged charge de-trapping times, leading to decreasing carrier concentration and incomplete charge collection. Based on the energy band theory, we elucidated the mechanisms underlying the interaction of the defects in CZT crystals. The study provides a foundation for the subsequent realization of effective modulation of defects through the crystal growth process.