Investigation on optical properties of SnxSbySz sulfosalts thin films

SnSb4S7, Sn2Sb6S11, SnSb2S4, Sn4Sb6S13, Sn2Sb2S5, and Sn3Sb2S6 single crystals were grown via the Bridgman technique and SnxSbySz thin films were obtained by a vacuum evaporation method onto non-heated glass substrates. Their structural and optical properties are studied by X-ray diffraction and transmittance and reflectance measurements in the wavelength range 300–1800 nm. X-ray diffraction (XRD) patterns indicate that polycrystalline SnxSbySz films were successfully obtained without heating the substrates. Optical measurements show that thin films of all materials have relatively high absorption coefficients between 104 and 2×105 cm−1 in the visible range and the higher values were obtained for Sn2Sb2S5 thin films. It is also found that the SnxSbySz films exhibit direct and indirect gaps Eg d and Eg ind which varied from 1.87 to 1.46 eV and from 1.71 to 1.37 eV, respectively. The dispersion behavior of the refractive index was studied in terms of the single-oscillator Wemple–DiDomenico and Cauchy models, and the optical parameters such as refractive index, extinction coefficient, oscillator energy, dispersion energy and Cauchy׳s constants were found. The electrical free carrier susceptibility and the carrier concentration of the effective mass ratio were estimated according to the model of Spitzer and Fan.