Compositional Dependence of the Optical Properties  of Amorphous Semiconducting Glass Se₈₀Ge_20−x Cd _x (0 ≤ x ≤ 12 at.%) Thin Films

Abstract

Se₈₀Ge_20−x Cd _x (0 ≤ x ≤ 12 at.%) compositions were prepared by a quenching technique. Thin films of the obtained compositions were deposited on dry clean glass substrates by a thermal evaporation technique. The chemical composition of the film samples have been determined by energy dispersive x-ray spectroscopy (EDX). X-ray diffraction measurements showed the amorphous nature of the studied films. The optical constants (n, k) were determined for the studied films using spectrophotometric measurements of transmittance T(λ) in the wavelength range (350 nm to 2500 nm), and using Swanepoel’s method. The values of the dispersion energy E _d, oscillator energy E _o, the lattice dielectric constant ε _∞L and the high-frequency dielectric constant ε _s were determined. The optical band gap $E_{g}^{\rm{opt}}$ is estimated for all compositions from the absorption coefficient α. The analysis of the optical absorption data revealed the existence of allowed indirect transitions for all compositions. The effect of adding Cd content on the obtained optical parameters was also discussed.