Bandgap tunability endowed by isovalent sulphur doping in SeTe glassy films: Correlation with Kastner's and single oscillator models

Thin films of sulphur (S) incorporated SeTe with chemical composition of Se80Te20-xSx (x = 0, 5, 10, 15, indicate the weight percentage of sulphur incorporated) were deposited via vacuum evaporation technique. S incorporation in the SeTe alloy led to reduction in the glass transition temperature from 333 K to 314 K. The investigated films were amorphous in nature with a thickness of similar to 250 nm. In comparison to pure selenium telluride (SeTe) film, the electrical conductivity exhibited an enhancement up to 10 wt % sulphur doping above which a decrease in electrical conductivity was apparent owing to microstructural porosity and enhanced bandgap. It is inferred that reduced grain size and dense morphology led to higher value of absorption coefficient as well as enhancement in the electrical conductivity. Interestingly, Te replacement with S results in monotonic increase in bandgap from 1.81 to 2.60eV and a reduction in absorption coefficient. The trend of the observed bandgap for the S incorporated samples is consistent with the Kastner and single oscillator models. (C) 2020 Elsevier B.V. All rights reserved.