Optical band gap in the system ZnO1 – xSx. An experimental and quantum chemical study

The synthesis of single crystalline and polycrystalline material is reported in the system ZnO1 – xSx. Substitution of oxygen by sulphur yields hexagonal wurtzite-type mixed crystals in the range 0 £ x £ 0.05. The cubic zincblende structure is observed for oxygen incorporation into ZnS for 0.96 £ x £ 1. At intermediate compositions, the system is two-phase. For both types of anion substitution, the band gap energies, as determined from optical transmission and remission experiments, are found to decrease from the pure end members. Quantum chemical calculations at density functional level identify local structural changes as the main factor responsible for the reduction of band gap energies.