Dielectric modelling of the transmittance spectra of thin As20S80 films

As20S80 thin films with different thicknesses (49.4–763.1 nm) were deposited on glass substrates using a thermal evaporation technique. Spectrophotometric measurements of the films' transmittance were taken in the wavelength range of 190–2500 nm. The transmission spectra were simulated with a computer model based on dielectric modelling to determine the optical constants and thicknesses of the films. The O'Leary–Johnson–Lim (OJL) models implemented in the commercial software programme SCOUT were used. Thicknesses obtained by the simulated method were correlated to the results obtained from a surface profiler technique. Optical parameters, such as the refractive index n, the absorption coefficient k, the optical band gap Eg, the high-frequency dielectric constant ε∞, the Urbach energy EU, the single-oscillator energy and the dispersion energy, were determined. The results indicated that the thickness effect can be separated into two distinct groups for films of thicknesses either less than or greater than 312 nm.