The interference modulated transmission spectra T( lambda ) at normal incidence for amorphous arsenic sulphide semiconducting films deposited by thermal evaporation were obtained in the spectral region from 300 nm up to 2000 nm. The straightforward analysis proposed by Swanepoel (1983), which is based on the use of the extremes of the interference fringes, has been applied in order to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Thickness measurements made by a surface profiling stylus have also been carried out to cross check the results obtained by the method employing only T( lambda ). In addition, the optical band gap Egopt has been determined from the absorption coefficient values using Tauc's procedure, i.e. from the relationship alpha (h nu )=K(h nu -Egopt)2/h nu , where K is a constant. Finally, it is emphasised that accurate results were achieved not only with the above mentioned glass composition As2S3, but also in the case of the non-stoichiometric composition As30S70.

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The optical transmission spectra of amorphous AsS films of composition As32S68 prepared by thermal evaporation are measured over the 0.3 to 2.0 μm spectral region. A simple straightforward procedure suggested by Swanepoel is applied for determining the index of refraction and layer thickness; the absorption coefficient is derived using the Connell and Lewis formulae based on the interference‐free transmittance. Furthermore, thickness measurements made by a surface profiling stylus are also carried out to cross‐check the results corresponding to the fringe pattern method. The dispersion of n is discussed in terms of the single‐oscillator Wemple and DiDomenico model and the absorption edge is described using the “non‐direct transition” model proposed by Tauc. Finally, the compositional trends of the refractive index, absorption coefficient, and optical band gap in the AsS chalcogenide glass system are analyzed in detail.

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The dispersive refractive index n(λ) and thickness d of chalcogenide glass thin films are usually calculated from measurements of both optical transmission and wavelength values. Many factors can influence the transmission values, leading to large errors in the values obtained for n(λ) and d. Anovel optical method is used to derive n(λ) and d for AsSe semiconducting glass thin films deposited by thermal evaporation in the spectral region where k(2) « n(2), using only wavelength values. This entails obtaining two transmission spectra: one at normal incidence and another at oblique incidence. The procedure yields values for the refractive index and average thickness of thermally evaporated chalcogenide films to an accuracy better than 3%.