Properties Of ZnO Prepared By Thermal Oxidation Of ZnS At A Low Temperature

Zinc oxide (ZnO) is an interesting â…¡-â…£ wide band gap (3.37eV) semiconductor material with wurtzite structure because of many properties, such as piezoelectricity and photoelectricity. Due to the large exciton binding energy of 60 meV, which ensures the high efficient excitonic emission at room temperature, it is regarded as one of the most promising materials for the ultraviolet (UV) and blue light emitting devices.Until now, ZnO has been grown with various methods such as pulsed laser deposition (PLD), radio frequency magnetron sputtering (RFM) and metal-organic chemical vapor deposition (MOCVD). Here, We fabricate polycrystalline ZnS thin films by plasma-assisted e-beam evaporation and then anneal them at low temperatures, so as to obtain ZnO and ZnO:S thin films.The PL and resonance Raman scattering spectra imply that the sample annealed at 600 ℃ is abnormal. Except the band coming from the free exciton radiant recombination, there is a new band, which locates at the low energy side. With the temperature enhanced the PL intensity is strengthen and domain the UV emission at room temperature. We also investigate the resonance Raman scattering properties of the samples. The shoulders which locate at the low Raman shift of the nLO phonon of ZnS are assigned as the disorder of the surface of samples and the smaller of the crystal the bigger of the ratio of the surface and the bulk which result in much higher shoulder. The modes, which are 72 cm^-1 distant from the nLO phonon of ZnS, are from the nLO+ E₂^L of ZnS. As for the ZnS samples which are bombed by oxygen and argon plasma for another five minutes after the evaporation, there are new narrow peaks which locate at 521 cm^-1 Raman shift. It may originate from the vacancy of S which needs further investigation.