Effect of the concentration of uncompensated impurities on the properties of CdTe-based X- and $\gamma$-ray detectors

Measurements of the $^{55}$Fe-isotope emission spectra and the photosensitivity of CdTe detectors with a Schottky diode, and also the temperature dependence of the resistivity of a CdTe crystal ((2–3) $\times$ 10$^9$ $\Omega$ cm at 300 K) have been used to determine the concentration of uncompensated donors (1–3) $\times$ 10$^{12}$ cm$^{-3}$. Similar measurements performed for Cd$_{0.9}$Zn$_{0.1}$Te crystals with the resistivity (3–5) $\times$ 10$^{10}$ $\Omega$ cm at 300 K have shown that the concentration of uncompensated donors in this case is lower by approximately four orders of magnitude. The results of calculations show that, due to such a significant decrease in the concentration of uncompensated donors, the efficiency of X- and $\gamma$-ray radiation detection in the photon energy range 59 to 662 keV can decrease by one-three orders of magnitude (depending on the photon energy and the lifetime of charge carriers in the space-charge region). The results obtained account for the apparent poor detecting properties of the Cd$_{0.9}$Zn$_{0.1}$Te detectors.