Influence of thickness on the optical properties of amorphous GeSe₂ thin films: analysis using Raman spectra, Urbach energy and Tauc parameter

Abstract

An analysis is reported of thickness-induced defects in amorphous GeSe₂ 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 GeSe₂ 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 GeSe_4/2 tetrahedra and edge-sharing Ge₂Se_8/2 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.

Keywords:

• vacuum deposition
• thin film structure
• morphology
• optical properties
• Raman spectra

Acknowledgements

The authors gratefully acknowledge the University Grant Commission (UGC), New Delhi, Govt. of India, for the financial support under the UGC project No. 37-270/2009(SR).