Optical parameter studies of thermally evaporated As-Se-Sn glassy system

The optical properties of As₃₀Se_70-xSn_x with (x = 0, 1, 2 and 3 at Sn %) thin films have been investigated. The films used in these studies were thermally evaporated. The structural characterization revealed that the as-deposited films were amorphous in nature. The spectral and optical parameters have been investigated using spectrophotometric measurements of transmittance in the wavelength range (200–1100 nm). The optical constants were determined from the interference maxima and minima using the Swanepole method. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-Didomenico model. The optical-absorption edge and the optical band gap are calculated from the absorption coefficient values using the non direct transition model proposed by Tauc’s extrapolation procedure. The relation between the optical gap and chemical composition in As-Se-Sn glassy system is discussed in terms of the average heat of atomization H_s and the average coordination number N_c.