Effect of thermal annealing on the structure and optical properties of Sn doped Ge₂₈Sb₁₂Se₆₀ chalcogenide glass films

Chalcogenide glass is widely used as a novel matrix material for photonic devices. The modification of the optical properties of chalcogenide glasses through thermal annealing has become a significant area of research. In this study, the effects of thermal annealing on the structure, morphology, linear and nonlinear optical properties of Sn-doped Ge₂₈Sb₁₂Se₆₀ (GSS) chalcogenide glass films were investigated. The Sn-doped GSS chalcogenide glass films were prepared by the co-evaporation method, and the as-prepared films were placed in a muffle furnace for annealing at 265 and 275 °C for 1 h. The structure and morphology of all the thin films were characterised by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results revealed that the as-prepared films exhibit amorphous characteristics, whereas the annealed films exhibit crystalline properties. The grains in the films became larger with annealing and the crystallinity improved. Additionally, the elemental composition and atomic percentages in the thin-film samples were confirmed by energy dispersive X-ray analysis (EDX) and were not significantly influenced by annealing. The optical parameters of the thin films were estimated using several empirical formulas based on the measured refractive indices and transmittances. As the annealing temperature increased, the optical bandgap decreased and the absorbance increased. Meanwhile, the values of nonlinear refractive index and third-order nonlinear polarisability of the thin films both doubled after annealing, increasing from 1.739 × 10⁻¹⁰ to 3.620 × 10⁻¹⁰ esu and from 1.269 × 10⁻¹¹ to 2.892 × 10⁻¹¹ esu, respectively. The results of this study have significant implications for the further study of the optical properties of chalcogenide glass films and the development of semiconductor materials for optoelectronic applications.