Structural and optical parameters of ZnSxSe1-x films deposited on quartz substrates by laser ablation

ZnSxSe1-x laser ablated films deposited on quartz substrates have been studied in order to obtain information on their structural and optical properties as a function of sulphur concentration (x). Transmittance and reflectance spectra at room temperature were carried out to obtain the energy gap modulation, the absorption coefficient and refractive index. By using the Newton-Raphson algorithm, the values of the real part of the refractive index in the transparent region were deduced including the effect of non-uniformity of the film thickness. The wavelength dependence of n was extrapolated for the weak and medium absorption range by means of two different models: the classical Cauchy formula and the single effective oscillator model proposed by Wemple and Di Domenico. From the latter theory, two physical parameters known as oscillator energy and oscillator strength, respectively, were obtained. These parameters have been related to the optical gap and structural properties of the deposited alloys. In the strong absorption region, the absorption coefficient and the optical gaps were calculated for each x-value. A quadratic trend was found for the x-dependence of the band gap, in agreement with the corresponding bulk alloy.