Effect of substrate temperature and post-deposition annealing on the properties of evaporated CdSe thin films

The structural, morphological and optical properties of vacuum-evaporated CdSe thin films were investigated as a function of the substrate temperature and the post-deposition annealing conditions. It was observed that the grain sizes and morphologies of as-deposited layers were similar for substrate temperatures of 100 and 200 K. However, CdSe films produced at a substrate temperature of 300 K had substantially different surface morphology. Annealing at 473-673 K in air did not cause any appreciable grain growth in any of the films irrespective of their growth temperature. However, annealing at 673 K initiated intergrain coalescence and altered surface morphology by reducing faceting. X-ray diffraction studies showed that the crystallinity of the CdSe films was improved upon annealing. The optical band gap energy values were obtained and two direct transitions were observed. This may be attributed to spin orbit splitting of the valence band. Resistivity measurements indicated that annealing at 673 K in air forms a highly resistive compensated CdSe film. The results showed that although the substrate temperature during growth plays the major role in determining the properties of deposited films, post-deposition annealing at temperatures of at least 673 K may lead to further changes in these properties. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)