Effect of annealing on the optical constants of Cd0.2Zn0.8Te thin films

The optical response of vacuum evaporated Cd0.2Zn0.8Te thin films in the 1.5-5.6-eV photon energy range at room temperature has been studied by spectroscopic ellipsometry. The films of Cd0.2Zn0.8Te were deposited at room temperature onto well-cleaned glass substrates of 1-μm film thickness. The measured dielectric-function spectra reveal distinct structures at energies of the E1, E1+Δ1 and E2 critical points corresponding to the interband transitions. The films annealed at higher temperatures show slightly lower value for the band gap. Dielectric related optical constants, such as complex refractive index, the absorption coefficients and the normal incidence reflectivity, are presented. Pinhole free thin films facilitated the analysis of high energy regions of the absorption coefficient spectra. Results are in satisfactory agreement with calculations over the entire range of photon energies