Based on the interference fringes in optical transmission spectra at normal incidence of different composition thin films As-S semiconducting glass, deposited by thermal evaporation, the direct analysis proposed by Swanepoel is applied for determining the real and imaginary parts of the complex index of refraction, and also the film thickness. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model, and the optical absorption edge is described using the 'non-direct transition' model proposed by Tauc. Likewise, the optical energy gap is derived from Tauc's extrapolation. Finally, the compositional trends of refractive index and optical band gap in different composition thin films As-S chalcogenide glass are interpreted in terms of the bond strengths of the chemical bonds present in the glass composition under study.
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