Semi-insulating cadmium telluride at low impurity concentrations

We report a substantial reduction in the impurity concentration of semi-insulating CdTe:Ge grown by the vertical Bridgman method by using sublimation of the feed material. Specific resistivity (ρdark) values of up to 3 × 109 Ω cm were obtained for samples with a relatively high photosensitivity (PS) value and optimal compensation. Concentrations of impurities in the feed and as-grown crystals were determined by the glow discharge mass spectroscopy (GDMS) method. The energy levels in the band-gap were studied by photoluminescence (PL), and the data were correlated with the GDMS measurements. The highest values of ρdark and PS were observed in the regions where the PL bands via the deep levels of Ge and Te antisite were present.