Optical parameter studies of as-deposited and annealed Se 1 − xTe x films

Abstract

Thin films of Se 1 − x Te x ( x = 0.2, 0.4, 0.6) are deposited on a glass substrate by thermal evaporation under vacuum. The optical gaps ( E g ) are determined from the absorbance and transmittance measurements in the visible and near IR spectral range (500–1100 nm), and are found to decrease with the tellurium concentration. After annealing at different elevated temperatures (423 K and 473 K), the values of optical gaps of Se 0.8Te 0.2 films, as a representative example, are also found to increase with temperature from 1.91 eV at room temperature to 1.97 eV at 473 K. This effect is interpreted in terms of the density-of-state model of Mott and Davis. The optical constants (extinction coefficient k, and refractive index n) were also determined. It was found that both n and k depend markedly on composition as well as the temperature of heat treatment. The valence band density of states of Se 1 − x Te x films is calculated from the optical absorption data.