The optical properties of thin films of cadmium and zinc selenides and tellurides

The optical constants n and k of thin polycrystalline films of CdSe, ZnSe, CdTe and ZnTe have been measured over the wavelength range 2000-300 nm. From analysis of the absorption data, the three cubic materials ZnSe, CdTe and ZnTe were found to have direct band-gaps with E_g=2.62, 1.50 and 2.23 eV respectively and spin-orbit splittings of the valence band of 0.48, 0.88 and 0.90 eV respectively. CdTe and ZnTe also have indirect band-gaps of 1.82 and 2.56 eV respectively. CdSe has a fundamental direct gap of 1.65 eV but the analysis of the absorption curve at higher energies was limited by the energy bands becoming non-parabolic.