New quaternary Bi30Sb10Se30Te30 thin films with enhanced photo current and surface wettability for optoelectronic applications

Bi-doped metal chalcogenides have important applications as thermoelectric and good optoelectronic devices. The present investigation is based on the optimization of various optical, structural, and electrical behaviours of quaternary Bi₃₀Sb₁₀Se₃₀Te₃₀ thin films via thermal annealing at different temperatures. The increased crystallite size and decreased dislocation density upon annealing were probed from the structural study. The contribution from the vibrational bonds in the sample with annealing was checked by Raman analysis. X-ray diffraction and high-resolution transmission electron microscopy studies confirmed the existence of the Sb₂Te and Bi₂Te₃ phases in the film. The granular structure of the compound was seen from the surface morphology. The X-ray photoelectron spectroscopy infers the chemical states of the elements in the sample. The reduction of optical bandgap from 0.94 eV to 0.52 eV upon annealing induced an increase in refractive index from 3.44 to 4.70, while the non-linear refractive index was found to be increased by three times, and the nonlinear susceptibility was increased by four times from the un-annealed condition. The hydrophilicity nature was sustained with annealing and also increased. An increase in photocurrent and a decrease in resistivity of the films with annealing were found from the I-V measurement, which is good for electronic devices. The optimized optical and electrical parameters make the annealed films suitable for various optoelectronic applications.