ELLIPSOMETRIC STUDIES OF MICROSCOPIC SURFACE-ROUGHNESS OF CDS THIN-FILMS

Analysis of changes in surface roughness of CdS thin films with prepar ation temperature was carried out using variable angle spectroscopic e llipsometry (VASE). The films studied were prepared by spray pyrolysis technique, in the substrate temperature range 200-360 degrees C. The VASE measurements were carried out in the visible region below the ban d gap (E(g) = 2.4eV) of CdS so as to reduce absorption by the him. The thickness of the films was in the range 500-600 nm. Bruggeman's effec tive medium theory was used for analysis of the surface roughness of t he film. The roughness of the film had a high value (similar to 65 nm) for films prepared at low temperature (200 degrees C) and decreased w ith increase in substrate temperature. This reached minimum value (sim ilar to 27 nm) in the temperature range 280-300 degrees C. Thereafter roughness increased slowly with temperature. The growth rate of the fi lms was calculated fbr different temperature ranges. It was found that the deposition rate decreases with the increase in substrate temperat ure and have an optimum value at 300 degrees C. Above this temperature deposition rate decreased sharply. The scanning electron micrograph ( SEM) of the film also showed that the film prepared at 280-300 degrees C had very smooth surface texture.