PHOTOLUMINESCENCE AND ABSORPTION STUDIES OF DEFECTS IN CDTE AND ZNXCD1-XTE CRYSTALS

We have studied at cryogenic temperatures photoluminescence features w hich lie more than 0.15 eV below the band edge in ZnxCd1-xTe (0 less-t han-or-equal-to x less-than-or-equal-to 0.09) crystals. The same featu res, namely a defect band which lies at about 0.13-0.20 eV below the b and-gap energy and a peak at 1.1 eV, that are observed in pure CdTe sa mples are observed in these alloy materials. In annealed samples we ob serve that the 1.1-eV feature, which has been attributed to tellurium vacancies, increases with fast cooling. Increased concentrations of te llurium vacancies can be understood in terms of the phase diagram of C dTe which indicates that higher concentrations of excess Cd appear in CdTe quenched from high temperatures. We also observe an absorption tr ansition near 1.1 eV by photothermal deflection spectroscopy (PTDS). T he PTDS phase shifts show that the deep defect is a bulk effect rather than a surface effect. The well-defined absorption peak suggests that the states contributing to the 1.1-eV transition are both localized. Our results also suggest that the defect band which lies 0.13 eV below the band gap (1.48 eV in CdTe) may also be related to tellurium vacan cies. However, the fact that the ratio of intensities between this def ect band and the 1.1-eV feature is highly variable suggests that the r elationship is not simple. The origin of the defect band and its phono n replicas remains controversial.