Cumulative effects of Te precipitates in CdZnTe radiation detectors

High-quality radiation detector-grade CdZnTe material is free from large-scale defects, such as grain boundaries, twins, and large Te or Cd inclusions (>50 μm), although it usually contains high concentrations of uniformly distributed Te inclusions and precipitates, typically of ∼20-μm-diameter size or smaller. We address the effects of the small-size Te precipitates on charge collection in CZT detectors, the significance of which is not yet well characterized. The strong correlation that we earlier found between the high-resolution X-ray maps and IR images proved that even small Te precipitates can trap substantial fractions of charge from the electron cloud. In this work, we modeled the transport of an electron cloud across idealized CZT devices containing Te precipitates to demonstrate that their cumulative effect can explain the degradation of energy resolution and the detection efficiency losses observed in actual CZT devices. Due to lack of experimental data on how the Te precipitates interact with an electron cloud, we developed a simplified (phenomenological) model based on the geometrical aspects of the problem. Despite its simplicity, the model correctly reproduced many experimental facts and gave quantitative predictions on the extent to which the presence of Te precipitates and inclusions can be tolerated. The broadening of the electron cloud due to repulsion and diffusion is at the core of the problem, making even low concentrations of small precipitates important in the device's performance.