Investigation of the optical and structural properties of thermally evaporated cadmium sulphide thin films on polyethylene terephthalate substrate

Cadmium sulphide (CdS) thin films of different thicknesses ranging from 100 to 400 nm were prepared on polyethylene terephthalate (PET) substrates at room temperature by thermal evaporation technique in vacuum of about 3×10⁻⁵ Torr. The structural characterisation was carried out by X-ray diffraction (XRD). These studies confirm the proper phase formation of the cadmium sulphide structure. The root mean square (RMS) roughness of the films was measured using atomic-force microscopy. The root mean square roughness of the films increases as the film thickness increases. The energy gap of CdS on PET substrates was determined through the optical transmission method using an ultraviolet–visible spectrophotometer. The optical band gap values of CdS thin films slightly increase as the film thickness increases. The optical band gap energy was found to be in the range of 2.41–2.56 eV.