The effect of Ag addition on the optical properties of Se 90Te 10 films

Abstract

Se 90Te 10− x Ag x (0 ≤ x ≤ 6) compositions were prepared by quenching technique. Thin films with different thicknesses of the obtained compositions were deposited on dry clean glass substrates by thermal evaporation technique. Energy dispersive X-ray spectroscopy (EDX) indicates that samples are nearly stoichiometric. X-ray diffraction patterns indicate that they are in the amorphous state. The optical constants, the refractive index n and the absorption index k, have been calculated from transmittance T and reflectance R through the spectral range of 400–2500 nm for the studied films with different thicknesses (165–711 nm). From the analysis of refractive index n data, high frequency dielectric constant ɛ ∞ was determined. Both ɛ ∞ and n are found to decrease with the increase of Ag content. The optical band gap E g opt is calculated for all compositions from the absorption coefficient analysis. The effect of the Ag addition on the obtained optical parameters has been discussed. The analysis of absorption index k data, revealed the existence of allowed indirect transitions for all compositions. It is indicated also that E g opt increase with increasing Ag content.