Infrared Measurements on CdS Thin Films Deposited on Aluminium

The reflectivity spectra of three CdS thin films (thickness 0.086, 0.33, and 0.66 μm) deposited on aluminium have been determined at room temperature. The measurements were carried out in the spectral range 180 to 740 cm−1, at an incidence of 45°, for light polarized with the electric field in the plane of incidence. A small absorption peak is observed near ωTO for the thicker samples, and a much stronger absorption peak near ωLO for all samples. The results are analysed in terms of the theory of Fuchs and Kliewer. The frequencies of the peaks and the partial widths associated with the virtual modes are in very good agreement with the theory. It is also found that the anharmonic width of the peaks is much larger than in CdS single crystals.