Sulfur in zinc telluride thin film : a new isoelectronic center

Isoelectronic center (IEC) forming deep level states in the forbidden gap can strongly enhance light emitting efficiency of semiconductors. In wide band gap II-VI compounds, recombination of excitons bound to IEC can even emit blue light, in which case IEC has a high potential in optoelectronic device application. Tellurium in ZnS is one of the well-studied IEC systems, where emission features have been assigned to the recombination of excitons localized at single, paired and cluster-like Te centers. Recently, the existence of bound state in ZnTe:S was also predicted but no experimental results are available for comparison. In this MPhil project, sulfur in ZnTe epitaxial layer grown on GaAs is studied with photoluminescence (PL) at various temperatures, excitation powers and under hydrostatic pressures, as well as time-resolved PL. A sulfur-related emission peak, labeled as P2, behaves as a deep level in hydrostatic pressure PL measurement, indicating that sulfur atoms form isoelectronic centers in ZnTe. The results agree with the theoretical prediction. Another emission band, labeled as P3, which shows a donor-acceptor pair characteristics possibly involves isoelectronic sulfur acting as a donor. A model is proposed to explain the emission mechanisms in the ZnTe1-xS[subscipt x] system