Optical and structural properties of thermally evaporated cadmium sulphide thin films on silicon (1 0 0) wafers

Cadmium sulphide (CdS) polycrystalline thin films were deposited on ultrasonically cleaned silicon wafers (1 0 0) by thermal evaporation technique in a vacuum of about 2 × 10−5 Torr. X-ray diffraction (XRD), Fourier transforms infrared (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), and spectroscopic ellipsometry (SE) were used to characterise the polycrystalline thin films. The thickness of the films as estimated by the ellipsometry, found to be in the range of 263–282 nm. The values of refractive index (n) and extinction coefficient (k) of thin films are found to decrease with wavelength. XRD results indicated the formation of cadmium sulphide thin films with hexagonal phase. The films have preferred orientation along (0 0 2) plane. The lattice parameters are calculated as a = 4.135 Å and c = 6.742 Å, which are in good agreement with the reported data. The optical properties of the polycrystalline thin films are investigated systematically by spectroscopic ellipsometry (SE) and a blue shift compared with bulk cadmium sulphide is observed. The optical band gap of the thin film is estimated to be 2.50 eV. The structural and optical properties of the films fabricated by the thermal evaporation technique are found to be desirable for optoelectronic devices.