Influence of thickness on the optical properties of amorphous GeSe <inf>2</inf> thin films: Analysis using Raman spectra, Urbach energy and Tauc parameter

An analysis is reported of thickness-induced defects in amorphous GeSe 2 thin films deposited by the vacuum evaporation technique. X-ray diffraction studies confirmed the amorphous nature of the thin films. Optical absorption measurements revealed an indirect transition with an energy gap that increases with film thickness. A blue shift in optical transmittance edges was observed in annealed GeSe 2 thin films. The obtained lower values of Urbach energy (E U) indicate that as thickness increases more ordered films can be produced. Raman spectra suggest that annealing promotes corner-sharing GeSe4/ 2 tetrahedra and edge-sharing Ge 2Se8/ 2 bi-tetrahedra bonding and leads to the reduction in disorder in bonding network, which is amply supported by the way of increase in band gap, increase in Tauc parameter (B 1/2) and reduction in E U from the analysis of transmittance spectra. Increasing the thickness promotes tetrahedral and bi-tetrahedral bonding through the reduction in bonding defects. © 2012 Copyright Taylor and Francis Group, LLC.