Effect of rapid thermal annealing on optical properties of zinc sulphide thin films

Zinc sulphide (ZnS) thin films were prepared on clean surface glass substrates by thermal evaporation under pressure of 10(-5) Torr. Thickness of thin films was uniform 55 nm measured by ellipsometry. These films were also kept into a quartz glass tube for rapid thermal annealing at 30 and 60 s by using a 500 W halogen lamp for crystalline the structure. The cubic structure of the films was verified by X-ray diffraction and the intensity of predominant peak increases with annealing time. The optical absorption study was carried out by UV-ViS-NIR spectrometer in the range of 200-800 nm. The optical band gap changes from 3.48 to 3.08 eV, with rapid thermal annealing. Thermo electric power studies confirm the n-type nature of ZnS thin films and thermoelectric power increases with increase in temperature. This study is important because ZnS is potentially important material for antireflection coating and window layer material in hetero-junction solar cells.