Abstract
Amorphous chalcogenide films of stoichiometric composition As 40S 60 have been prepared by three different deposition techniques, namely, vacuum thermal evaporation, plasma-enhanced chemical vapour deposition (PECVD) and spin coating. Indications of film-thickness inhomogeneities were found in all samples. Thermally evaporated and chemically deposited samples showed wedge-shaped surface profiles, while significant surface roughness was evidenced in the spin-coated ones. Refractive-index values of the film samples were obtained, with accuracy better than 1%, by using the envelope method most suitable for each particular film surface profile. Structural information of the samples has been gained from X-ray diffraction experiments, and also inferred from the analysis of the dispersion of the refractive index, on the basis of a single-oscillator model. Analysis of the optical absorption spectra allowed both calculating the optical band gaps and estimating the localised-state tail width of these semiconducting films. In addition, information about the degree of structural randomness of these thin-film amorphous alloys was also obtained from this analysis, which is in good agreement with the conclusions derived from the X-ray diffraction results.
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