Resonant Raman scattering and photoluminescence from high-quality nanocrystalline ZnO thin films prepared by thermal oxidation of ZnS thin films

In this paper. we report photoluminescence (PL) from high-quality nanocrystalline ZnO thin films. The high-quality nanocrystalline ZnO thin films are prepared by thermal oxidation of ZnS films deposited by low-pressure metal organic chemical vapour deposition technique. X-ray diffraction indicates nanocrystalline ZnO thin films with a polycrystalline hexagonal wurtzite structure. The Raman spectrum shows a typical resonant multi-phonon process within the ZnO film. A strong ultraviolet emission peak, at 380 nm is observed and the deep-level emission band is barely observable at room temperature. The strength (Gamma(LO)) of the exciton-longitudinal-optical (LO)-phonon coupling is deduced from the temperature dependence of the full width at half maximum of the fundamental excitonic peak. Gamma(LO) is largely reduced due to the quantum confinement effect. The origin of the luminescence is discussed with the help of PL spectra.