Role of Te on the spectroscopic properties of As50Se40Te10 thin films: An extensive study by FTIR and Raman spectroscopy

Amorphous As50Se50 and As50Se40Te10 thin films were prepared on glass substrates by using thermal evaporation method. The transmission spectra T (λ) of the films at normal incidence were measured in the wavelength range 400-1100 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the refractive index(n) and the extinction coefficient(k). The addition of Te into As50Se50 is found to increase the refractive index and the extinction coefficient of the As50Se40Te10 films. With the addition of Te into As50Se50, the optical band gap decreases due to the increase in disorderness. The urbach energy and tauc parameter is changed due to the Te incorporation which measures the disorderness. The optical absorption is due to allowed indirect transition and the chemical bond approach has been applied successfully to interpret the decrease of the optical gap. The Raman shift observed in the two films clearly supports the optical changes due to Te addition.