A Study of Impurities (Ag, Bi & Ge) on the optical properties of Se-Te thin films

Abstract

Thin films of chemical composition Se80Te20, (Se80Te20)98Ag2, (Se80Te20)98Bi2 and (Se80Te20)98Ge2 are prepared by thermal evaporation technique. The optical properties of these thin films are determined by a method, based only on the transmission spectra at normal incidence, measured over the spectral range of 500-2500 nm. The dispersion of refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model. Optical energy gap (Eg) decreases while refractive index (n) increases on the incorporation of Bi addition in Se-Te system. On the other hand Eg increases while n and extinction coefficient (k) decreases on incorporation of Ag and Ge in Se-Te system. Results are interpreted in terms of cohesive energy (CE) and electronegativity (χ).