Optical and dispersion parameters of co-evaporated SnS0.7Se0.3 thin films

Tin sulfoselenide (SnS1-xSex) is a novel ternary semiconductor that belongs to the IV – VI group of compounds. It possesses the properties of both SnS and SnSe, which are proved as good absorber materials for solar cell fabrication. In the present work, SnS0.7Se0.3 thin films were deposited by vacuum co-evaporation technique at four different substrate temperatures (Ts), 200 °C, 250 °C, 300 °C and 350 °C. The optical properties of as-deposited SnS0.7Se0.3 films were analyzed using optical measurements. From the optical transmittance and reflectance data, the band gap energy of the layers was determined that varied in the range, 1.59–1.46 eV. The other optical parameters such as skin depth, refractive index, extinction coefficient, optical conductivity and dielectric constant of SnS0.7Se0.3 layers were determined and discussed as a function of substrate temperature. Moreover, the dispersion parameters of the layers were also evaluated using Wemple – DiDomenico (WDD) single oscillator model. The dispersion energy (Ed) and oscillator energy (Eo) of the films were evaluated and varied in the range, 2.19–2.38 eV and 7.55–9.52 eV respectively. Moreover, the optical dispersion moments (M−1 and M−3) were also calculated that were varied from 0.25 to 0.29 and from 2.76 × 10-3 to 5.08 × 10-3 respectively.