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 GeSe4/2 tetrahedra and edge-sharing Ge2Se8/2 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.
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).