Enhanced Photoresponse from Ag/Bi₂Se₃ Heterostructure Thin Films under Thermal Annealing

Abstract

Semiconducting transition metal chalcogenides (TMCs) have shown great potential for optoelectronics applications due to their strong light absorption in a broad spectral range. Increasing the photoresponse ability of thin films is very much essential for many applications. The current study reports the increase in photoresponsivity and detectivity of annealed Ag/Bi₂Se₃ film by many folds from its as-deposited state. The thermally evaporated bilayer film of Ag/Bi₂Se₃ was annealed at different temperatures and was characterized by X-ray diffraction (XRD) and Raman study for structural changes in the films. The increase in crystallinity affects the structural parameters. The observed phases were verified using the high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns. The bilayer heterostructure and the Ag diffusion were probed from the cross-sectional field emission scanning electron microscope (FESEM) image and were and the surface morphology through the FESEM study. The elemental presence was confirmed from the energy-dispersive X-ray spectroscopy (EDX) data, whereas a ultraviolet–visible (UV–vis) spectrophotometer was used for the optical measurements. The reduction in transmittance upon annealing influenced several other optical parameters, and there is a reduction in band gap from 1.5 to 1.17 eV upon annealing. The third-order nonlinearity and nonlinear refractive index increased 2-fold, with the enhancement of the linear refractive index upon annealing. The hydrophobicity tendency is enhanced upon annealing, as found from the contact angle measurement. The photoresponse efficiency increased from 9.94 × 10^–7 AW^–1(as-deposited) to 2.72 × 10^–1 AW^–1, and detectivity increased from 1.48 × 10⁷ Jones (as-deposited) to 6.68 × 10⁹ Jones for the 250 °C annealing. Both the dark and light current increased from nA to mA upon annealing at 250 °C. These findings establish a framework for designing and optimizing analogous materials, advancing their utility in next-generation optoelectronic applications requiring high sensitivity and energy efficiency.