Special features of conductivity of semi-intrinsic CdTe and CdZnTe single crystals used in X- and γ-ray detectors

The temperature dependences of the resistivity of detector-grade semi-insulating CdTe and Cd0.9Zn0.1Te single crystals were investigated. The investigations have revealed that the thermal activation energy can be higher than Eg/2 at T → 0 K or considerably less than this value, although the Fermi level is located near the middle of the band gap. It is shown that such an “anomalous” behavior of the electrical characteristics is explained in detail by the features of the compensation of deep acceptor levels in the semiconductor band gap. A method based on the electroneutrality equation is proposed for the determination of the ionization energy and compensation degree of the impurity (defect), which is responsible for the conductivity of the material. The results extracted with the use of this method lead to the prediction that the inversion of the conductivity type of the semiconductor under certain conditions can occur as the temperature varies during operation of a Cd(Zn)Te-based device.