Three-Dimensional Mapping of Carrier Lifetime and Mobility

Since the quality of CdZnTe (CZT) material for semiconductor detectors improved, it has become a widely used compound for high-resolution room temperature detectors. Today CZT detectors are used in a wide range of applications, from industrial and medical imaging to detectors used in high-energy particle physics and astrophysics. Despite the many advantages of the compound material, the material suffer from ineffective charge collection due to charge trapping, difficulty of producing large-area defect-free single crystals, material inhomogeneity, and lastly poor hole movement compared to electron movement. Different techniques exist to estimate the electron and hole mobility and lifetime inside a CZT detector. This is important not only to understand the performance of the detector in question but also to compare CZT quality of different material samples used for the detector fabrication. We will in this chapter review some of the conventional techniques used for extracting the material mobility and lifetime µt and thereafter present the determination of 3D electron mobility and lifetime maps of a 3D position-sensitive CZT detector. The 3D maps are computed by combining µt-extraction methods together with 3D high-resolution position and energy information provided by the detector. The 3D maps can be used as look-up tables for the model, to more precisely predict the pulse shape formation. In conclusion, the model performance is compared to real event data, showing that the model predictions are in agreement with generated pulse shapes.