Structural and optical characteristics of CdS thin films deposited by infrared pulsed-laser technique

The influence of preparation conditions on the structure and optical properties of cadmium sulphide (CdS) thin films deposited on quartz substrates by means of the pulsed laser technique have been investigated. Oriented growth of hexagonal CdS nanoparticulate film with the C-axis perpendicular to the plane of the surface has been achieved up to a film thickness of 220 nm. The results indicate that the heat treatment played an important role on both crystal structure and optical properties. The grain size and the crystallinity of the films were increased, as well as the optical energy gap E opt g (allowed direct transitions) was increased from 2.45 to 2.50 eV upon annealing. The dispersion of the refractive index of virgin and annealed films were estimated and explained using the Wemple-Didomenico (WD) single-oscillator model. The dispersion parameters and the free charge carrier concentrations were also estimated.