Optical properties of thin-film ternary Ge10As15Se75 chalcogenide glasses

The optical properties of ternary chalcogenide amorphous thin films of chemical composition Ge10As15Se75, deposited by vacuum thermal evaporation, have been determined and analysed, Normal-incidence optical transmission spectra have been measured in the range from 400 to 2500 nm. From these transmission spectra, the optical constants and average thickness of this particular amorphous ternary material were accurately calculated using an optical-characterisation method based on creating the upper and lower envelope curves of the spectrum, which also allows to obtain a parameter indicating the degree of film-thickness uniformity. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model, The optical-absorption edge is described using the non-direct transition model proposed by Tauc and the optical band gap is calculated from the absorption coefficient values by Tauc's extrapolation procedure. A comparison between these optical properties and those corresponding to the As30Se70 and Ge25Se75 binary thin films (previously reported) is also presented. (C) 1999 Elsevier Science B.V. All rights reserved.