Influence of Te replacement by Bi in In10Se70Te20-xBix films and its structural, optical, morphological, surface wettability and thermal behaviors for optoelectronic applications

Abstract

The current investigation is based on Bi doping into In–Se–Te alloy and its impact on the surface morphology, structure, and optical behaviors. The transition from In10Se70Te20 to In10Se70Bi20 composition modified its structural phases as observed from X-ray diffraction study. The crystallite size increased from 9.55 nm to 14.04 nm. The lattice strain decreased from 0.0234 to 0.0106 with Bi content. Raman study infers the microstructural and phase formation in the films. The structure change is associated with change in surface morphology as noticed from field emission scanning electron microscopy images. The composition of In10Se70Te20-xBix (x = 0, 5, 10, 15, 20 at %) films were observed from energy dispersive X-ray analysis. The UV–Vis–NIR data showed the decrease in transmittance from 80 % to 10 % at 2100 nm wavelength with Bi%. The decrease in direct bandgap from 1.64 eV to 1.37 eV was discussed by Davis-Mott model for density of defect states. The increase in Urbach energy from 101 meV to 161 meV is based on the transition from In10Se70Te20 to In10Se70Bi20 composition. The optical parameters like optical density, extinction coefficient and absorption coefficient were increased with Bi addition. The calculated static linear refractive index by different model at different Bi% satisfies Moss's relation. The enhanced non-linear susceptibility from 2.96 × 10−10 esu to 3.33 × 10−10 esu and non-linear refractive index from 1.58 × 10−7 esu to 1.86 × 10−7 esu with Te replacement by Bi may be suitable for non-linear optical devices. The change in different theoretically calculated physical parameters were found to be in accordance with the experimental data. The surface wettability study showed the transition from hydrophilic to hydrophobic nature with increase in Bi %. The obtained experimental results for the films may be used for various photonic and optoelectronic device applications.