The optical constants of thin evaporated films of cadmium and zinc sulphides

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Abstract
The optical constants n and k have been determined over the wavelength range from 2000-250 nm by measurements of reflectance and transmittance at normal incidence and treating these data by the method of Denton et al. (1972). The effects of surface roughness have been taken into account. Analysis of the dependence of absorption on photon energy have shown that the experimental results may be explained by the occurrence of direct transitions from 2.42 eV to 2.82 eV, in the case of CdS, followed by combined direct and indirect transitions beyond 2.82 eV assuming the energy band to be parabolic, or equally well by assuming only direct transitions between nonparabolic bands. The results for ZnS films are similar and may be treated in the same way. It is concluded that these materials both show absorption by direct transitions just beyond the absorption edge, and that at higher energies the form of the absorption curve is probably due to the combined effects of indirect transitions together with direct transitions between nonparabolic bands.

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