Optical properties of amorphous thin film of Se-Te-Ag system prepared by using thermal evaporation technique

Optical reflection and transmission spectra of Se80−xTe20Agx (where x=0, 5, 10 and 15, molar percent) chalcogenide thin films have been obtained in the range 300–1 200 nm at room temperature. Glassy samples are prepared by melt quenching technique and thin films are obtained by using vacuum evaporation technique on glass transition at room temperature. The present paper reports the effect of Ag contents on various optical parameters such as optical band gap, refractive index, extinction coefficient, absorption coefficient. Reflection spectra are used for calculating these optical parameters. The band gap Eg is determined from the plot of (αhν)1/2 versus hν. Real and imaginary parts of the dielectric constant changes slightly with the variation of Ag contents in different samples. The film exhibits indirect band gap which increases with increasing Ag content. The observed behavior is explained on the basis of Davis and Mott model for the density of states. The absorption coefficient of thin films exhibits linear dependence on photon energy. Other optical parameters are calculated by using theory of reflectivity. All the optical parameters change with the variation of the film composition. Computerized spectrophotometer JASCO-UV/VIS/NIR is used to determine optical constants.