Optical properties of CdSxTe1-x polycrystalline thin films

Thin films of CdSxTe1-x (0 less than or equal to x less than or equal to 1) have been prepared by vacuum evaporation from solid solutions. Rutherford backscattering spectrometry has been used to determine the thickness of the films, which is in the range 8-50 nm, and x-ray diffraction analysis has b een used to determine the phase. The refractive index and extinction coeffi cient of the films has been calculated from reflectance and transmittance m easurements for the wavelength region 250-3200 nm. Polynomial functions are given for each sample, which describe the variation in refractive index an d extinction coefficient over the entire wavelength range. Least squares fi tting to the absorption spectra revealed that the films all have a direct b and gap, although photon energies required for indirect transitions have al so been found. CdS0.8Te0.2 is found to have the lowest absorption coefficie nt at energies greater than 2.1 eV.