Optical Properties of Tellurium as an Isoelectronic Trap in Cadmium Sulfide

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Abstract
Optical fluorescence and absorption associated with tellurium, an isoelectronic trap in CdS, are described. At low temperatures two fluorescence bands can appear: one, with a peak near 6000 Å, occurs in lightly doped crystals containing less than 1019 Te atoms/cm3; the other, with a peak near 7300 Å, occurs in more heavily doped crystals. The temperature dependencies of the fluorescence decay times of both bands were measured and compared with various models for the recombination mechanisms. It is concluded that the 6000-Å band arises from bound hole-electron recombination at isolated tellurium atoms on sulfur sites, while the 7300-Å band is probably associated with recombination at pairs of tellurium atoms on nearest neighbor sulfur sites. At room temperature, the quantum efficiency for electron-beam excited fluorescence of of 7300-Å band can be near unity. The reasons for the high efficiency are discussed.