Inhomogeneous Resistivity and Its Effect on CdZnTe-based Radiation Detectors Operating at High Radiation Fluxes

Cadmium telluride (CdTe) and its compounds are the materials of choice for producing industrial quality hard x-ray and gamma ray detectors with high spectral resolution and signal-to-noise ratio. However, optimization of the growth process still proves challenging as the yield is small due to inhomogeneities in the material parameters. Here we investigated the influence of inhomogeneous resistivity on charge collection efficiency of CdZnTe radiation detectors operating at high photon fluxes of incoming radiation. We applied a complex of experimental methods-contactless resistivity and photoconductivity mapping, photoluminescence and laser-induced transient current technique. We observed that the charge collection efficiency at low fluxes is nearly independent of resistivity, while at high fluxes the performance of high resistivity part substantially decreases when compared to the lower resistivity part. This behavior is explained by characteristic evolution of defect structure attaining shallow defect self-compensation during the cooling of the solidified crystal. Instabilities at impurity segregation and temperature gradients at the crystal growth cause different concentration of defects that manifest themselves as deep energy levels within the material bandgap. The defect self-compensation is successfully simulated by theoretical model considering defect reactions in tellurium-saturated CdZnTe.