Investigation of Deep Levels in CdZnTeSe Crystal and Their Effect on the Internal Electric Field of CdZnTeSe Gamma-Ray Detector

A study of deep levels in CdZnTeSe radiation-detection materials is presented. The approach relies on electrical methods that combine time and temperature evolution of the electric field and electric current after switching on the bias voltage. Two optical methods were also applied to study the deep levels. The first method utilizes the temperature and temporal analysis of the electric field evolution after switching off an additional light illuminating the sample at a wavelength of 940 nm. The second method involved measuring of the electric field spectral dependence during near infrared illumination. The results are compared with those obtained with the high-quality CdZnTe detector-grade material. We conclude that the introduction of Se into the lattice leads to a shift of the second ionization level of the Cd vacancy toward the conduction band, as predicted recently by first-principles calculations based on screened hybrid functionals.