No abstract

No abstract

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.

The structural, morphological and optical properties of vacuum-evaporated CdTe thin films were investigated as a function of substrate temperature and post-deposition annealing without and with CdCl 2 /treatment at 400°C for 30 min. Diffraction patterns are almost the same exhibiting higher preferential orientation corresponding to (111) plane of the cubic phase. The intensity of the (111) peak increased with the CdCl 2 /annealing treatment. The microstructure observed for all films following the CdCl 2 /annealing treatment are granular, regardless of the as-deposited microstructure. The grain sizes are increased after the CdCl 2 /annealing treatment but now contain voids around the grain boundaries. The optical band gaps, E g , were found to be 1.50, 1.50 and 1.48 eV for films deposited at 200 K and annealed without and with CdCl 2 /treatment at 400°C for 30 min respectively. A progressive sharpening of the absorption edge upon heat treatment particularly for the CdCl 2 /treated was observed.

No abstract