The effect of deep-level defects is a key issue for the applications of CdZnTe high-flux photon counting devices of X-ray irradiations. However, the major trap energy levels and their quantitive relationship with the device’s performance are not yet clearly understood. In this study, a 16-pixel CdZnTe X-ray photon counting detector with a non-uniform counting performance is investigated. The deep-level defect characteristics of each pixel region are analyzed by the current–voltage curves (I–V), infrared (IR) optical microscope photography, photoluminescence (PL) and thermally stimulated current (TSC) measurements, which indicate that the difference in counting performance is caused by the non-uniformly distributed deep-level defects in the CdZnTe crystals. Based on these results, we conclude that the CdZnTe detectors with a good photon counting performance should have a larger Te cd 2 + and Cd vacancy-related defect concentration and a lower A-center and Tei concentration. We consider the deep hole trap Tei, with the activation energy of 0.638–0.642 eV, to be the key deep-level trap affecting the photon counting performance. In addition, a theoretical model of the native defect reaction is proposed to understand the underlying relationships of resistivity, deep-level defect characteristics and photon counting performance.

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An experimental method was described to calibrate the depth of interaction (DOI) of high-energy γ -ray in large-size thick pixel CdZnTe detector. The experimental results indicated that the ratio of the cathode and anode amplitude strongly showed linear relationship with the DOI of incidence γ -rays and the detector. The correlation coefficients were optimized. Based on the experimental calibration of DOI, the photoelectric effect signals from the depth range where the energy resolution and the photopeak location are high were screened out to draw the energy spectrum. In this way, the energy resolution of the CdZnTe pixel detector was improved to 0.707% for 137 Cs@662 keV. Further combined with the anode rise time, the electron mobility of CdZnTe in 2-D (1 mm accuracy) and 3-D (2 mm × 2 mm × 1 mm accuracy) scales was calculated. At different pixel positions and depths in CdZnTe detector, the electron mobility varies between 1000 and 1150 cm 2 /(V•s).