Modelling the effects of Te precipitates on the electron transport in CdZnTe radiation detectors

Large Te inclusions, >100 μm, or aggregations of Te precipitates are known to degrade the performance of CdZnTe (CZT) nuclear-radiation detectors. At the same time, it is widely accepted that randomly distributed small Te precipitates are not harmful. Previous attempts to study Te precipitates, conducted with wide X-ray or alpha-particle beams, were unable to reveal their critical role because the 300–400 μm diameter excitation probes used in the experiments were much larger than the 10–20 μm diameter Te precipitates. In contrast, our recent measurements carried out with high-spatial resolution, <10 μm, mapping techniques provided clear evidence that even small-size precipitates adversely affect the energy resolution and detection efficiency of CZT devices. In our model, Te precipitates were treated as non-transparent spherical areas randomly distributed inside a CZT crystal. As an electron cloud drifts toward an anode and grows due to diffusion, the Te precipitates trap a fraction of the total charge corresponding to the footprints of the different precipitates along the path of the electron cloud projection. Thus, the charge loss due to Te precipitates is mainly modeled as a geometrical effect. Here, we describe the application of this simple approach to model the charge loss due to Te precipitates and describe how it affects the detector's performance for realistic devices. We compare the predicted results with the experimental data.