25 September 2014 Band gap dependence upon thickness of chalcogenide Ge-As-S thin films
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Proceedings Volume 9288, Photonics North 2014; 92880K (2014) https://doi.org/10.1117/12.2075126
Event: Photonics North 2014, 2014, Montréal, Canada
Abstract
We have studied thin films of Ge25As30S45 glass evaporated by electron-beam technique. We have analyzed the transmission spectra of thin films of the same nominal composition, obtained under identical conditions, but with four different thicknesses varying from 1 to 7 micrometers. All fabricated films were annealed for 1h at 300oC (below the glass transition temperature of this glass). As a result, we observed a thickness dependent blue-shift of about 100 nm of their transmission edge. We have calculated the optical band gap of those annealed thin films and we have observed that the slope of absorption edge becomes less abrupt and the band gap decreases when their thickness increases. Furthermore, this band gap decrease is accompanied with a broadening of the tails and localized states, which indicates an increase of the degree of disorder in the vitreous network. This could be explained by the higher density of defects and dangling bonds in the thinner films since the amount of deposited material is smaller. This implies therefore an increase of both the degree of disorder and the concentration of defects, and consequently the decrease of the optical gap.
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K. Palanjyan, R. Vallée, T. Galstian, "Band gap dependence upon thickness of chalcogenide Ge-As-S thin films", Proc. SPIE 9288, Photonics North 2014, 92880K (25 September 2014); doi: 10.1117/12.2075126; https://doi.org/10.1117/12.2075126
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