Structural and optoelectronic properties change in Bi/In2Se3 heterostructure films by thermal annealing and laser irradiation

Abstract

The amorphous materials are sensitive to external radiations and thermal annealing that brings changes in their structural and optical properties for optoelectronic applications. The present report shows the amorphous to crystalline structure transformation in Bi/In₂Se₃ by energy radiation and thermal annealing that modifies the linear as well as the nonlinear optical properties. The thermally evaporated Bi/In₂Se₃ film was subjected to 2.35 eV energy irradiation and 150 °C thermal annealing. The structural transition was probed by XRD, which revealed the formation of BiSe, Bi₄Se₃, and Bi₂Se₃ phases by replacing indium with an average crystallite size of ∼20 nm. The diffusion of Bi into In₂Se₃ host matrix modified the interfacial region as noticed from the field effect scanning electron microscopy pictures. The linear and nonlinear optical constants were evaluated from the UV–Visible data that show a significant change in the irradiated and annealed films due to the new phases. The change in direct and indirect bandgap is explained on the basis of density of defect states and degree of disorder. The significant change in the refractive index brings more freedom in designing multifunctional optoelectronic devices. The σ_opt and σ_elect changed noticeably with heat and energy treatment. The high value of χ³ (18.81 × 10⁻¹⁰ esu) for the Bi/In₂Se₃ film decreased significantly to 3.68 × 10⁻¹⁰ and 2.13 × 10⁻¹⁰ esu for the annealed and irradiated film. All the optical parameter changes due to annealing and irradiation are confined between the two-host materials In₂Se₃ and Bi/In₂Se₃. The corresponding changes were also observed in Raman spectroscopy data. The tuning of these linear and nonlinear parameters is useful for optoelectronics and photovoltaics.