Optical properties of the new material Sn2Sb6S11 thin films deposited by thermal vacuum evaporation

Abstract

The purpose of this work was to investigate the effect of substrate temperature on the structural and optical properties of Sn2Sb6S11 thin films. Sn2Sb6S11 thin films have been deposited by single source vacuum thermal evaporation onto glass substrates at various substrate temperatures in the range 30–200°C. By X-ray diffraction analysis, an improvement on the structural properties by increasing the substrate temperature was observed. The reflectance and transmittance of the films are measured in the incident wavelength range 300–1800 nm. The absorption coefficients of the Sn2Sb6S11 thin films are in the range of 105–106 cm−1. The analysis of the absorption coefficient in the high absorption region revealed two direct forbidden band gaps Eg1 and Eg2 in the ranges 1·58–1·72 and 1·75–1·88 eV respectively. It has been found that the refractive index dispersion data obeyed the single oscillator of the Wemple–DiDomenico model. Using this model, the dispersion parameters and the high frequency dielectric constant were determined. The low value of the extinction coefficient is a qualitative indication of excellent surface smoothness of the films. The electric free carrier concentration on the effective mass ratio was estimated according to the model of Spitzer–Fan.