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.

Keywords:

• Ternary system
• Sn₂Sb₆S₁₁
• Vacuum deposition
• X-ray diffraction
• Thin films
• Glasses
• Structural and optical properties