Factors limiting lifetime of charge carriers in semi-insulated CdTe under high radiation flux

Abstract

With the growing interest in CdTe and (CdZn)Te X-ray detectors operating at high fluxes of X-ray photons (∼10 10 cm −2 s −1) the questions arises, whether the lifetime of charge carriers is limited by trapping and recombination at deep levels or by band-to-band recombination due to a strongly elevated concentrations of free electrons and holes compared to detectors working at low fluxes. A set of numerical simulations was done to resolve this question. The approach is based on the self-consistent steady state solution of electron and hole drift-diffusion equations using an iterative method. The effect of space charge on the electric field distribution and carrier transport through the sample is evaluated by solving the Poisson equation. The material simulation parameters were chosen to describe typical situations in state-of-the art highly compensated semi-insulated CdTe and CdZnTe (∼10 10 Ωcm) with deep near-midgap levels with concentrations in the range of 10 11–10 12 cm −3.The band-to-band recombination parameter was calculated using the Van Roosbroeck–Shockley relation and was estimated ∼3×10 −10 cm 3/s. The results show, that under all studied conditions the lifetime of carriers and thus the detector performance is limited by carrier trapping and recombination at deep levels.