Microstructural effects of thermal annealing on CdS films

Thin solid films of CdS chemical bath deposited on glass substrates were analyzed by spectroscopic ellipsometry in the spectral range of 1.5-5.0 eV, before and after thermal annealing in Ar atmosphere, at different temperatures, Analyses of the data reveal that the films possess a multilayer structure of two or three layers, The samples which were as-grown and thermal annealed at 208 degrees C are described by cubic phase layers of CdS. For temperatures of thermal annealing greater than or equal to 260 degrees C, the films are better described by layers in the hexagonal phase of CdS. The as-grown sample shows features of three graded density-deficient layers. As the annealing temperatures increases, the density and size of the layer closest to the substrate increases, while the other two remain as density-deficient layers. The sample annealed at the maximum temperature (447 degrees C) is described by just two layers. All the spectra of the thermally treated samples show a shift in the optical band gap with respect to the as-grown sample. These results are compared with the analyses of previous works. (C) 1996 American Institute of Physics.