Optical characterization of amine-solution-processed amorphous AsS2 chalcogenide thin films by the use of transmission spectroscopy

Amorphous thin layers with non-stoichiometric chemical composition As33S67 (AsS2) have been prepared by spin coating. This particular deposition technique is a very promising, low-cost technique, to create optical-grade, chalcogenide glass thin films, which are certainly ideal for visible and infrared applications. The layer thickness and optical constants have been first determined by the Swanepoel transmittance-envelope method, for the case of uniform thin films, with an accuracy better than 1%. The refractive-index dispersion has been analyzed on the basis of the Wemple-DiDomenico single-effective-oscillator model: n2(E)=1+E0Ed/(E02−E2), where E0 is the single-oscillator energy and Ed the dispersion energy. The strong-absorption region of the absorption edge is described using the 'non-direct electronic transition' model, proposed by Tauc. Structural information of the AsS2 bulk and thin-layer samples has been gained from X-ray diffraction measurements, and, also, from the analysis of the refractive-index dispersion. In addition, the simulation software WVASE32 was successfully utilized in fitting the experimental, normal-incidence transmission data by the use of Tauc-Lorentz model; an excellent fit between the measured and software-generated optical transmission spectra has been generally achieved, with a mean-squared-error as low as around 0.4.