Improvement of hydrophilicity and optical nonlinearity in a Te/In2Se3 bilayer heterostructure film by annealing at different temperatures for optoelectronic applications

Abstract

Group III–VI semiconductor materials have unique properties for photodetector and optoelectronic devices. The present work is based on the formation of Se–In–Te alloys from the bilayer Te/In₂Se₃ heterostructure by annealing at various temperatures. The heterostructure and its conversion to a layer alloy were verified from the cross-sectional view taken by FESEM. The surface morphology shows a reduction in nanoparticle size with annealing temperature. EDX confirmed the In, Se, and Te existence in the film structure. The existence of different phases of In₂Se₃ and Te was found from the structural investigation through XRD and HRTEM. The increase in crystallinity and decrement in dislocation density influenced the optical properties of the film by reducing the transmittance by 50% and increasing the extinction coefficient upon annealing. The optical density increased with a decrease in optical bandgap upon annealing, thus increasing the refractive index. The hydrophilicity nature increased to a super hydrophilic one at a high annealing temperature. The χ⁽³⁾ value increased from 1.164 × 10⁻¹⁰ to 1.680 × 10⁻¹⁰ esu, and the nonlinear refractive index enhanced from 1.244 × 10⁻⁹ to 1.721 × 10⁻⁹ esu upon annealing. The change in photoconductivity upon annealing is very useful for visible light photodetection.