Effect of the concentration of uncompensated impurities on the properties of CdTe-based X- and γ-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) × 10 9 Ωcm at 300 K) have been used to determine the concentration of uncompensated donors (1–3) × 10 12 cm −3 . Similar measurements performed for Cd 0.9 Zn 0.1 Te crystals with the resistivity (3–5) × 10 10 Ω 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 γ-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.