Abstract
•Optical and structural parameters of thermally evaporated and annealed Ge20Se70Sn10 of thin films are determined and discussed.•The indirect band gap energy was decreased from 2.1 to 0.94 eV as the annealing temperature increased from 503 to 703 K.•The nonlinear optical susceptibility and nonlinear refractive index were determined by means of the linear optical parameters in the long-wavelength boundary.•The relationship between the Tauc gap and nonlinear refractive index was discussed in detail.
This study reposts the influence of annealing temperature (TA) on structural and optical properties of ~150 nm thick Ge20Se70Sn10 films. Amorphous Ge20Se70Sn10 films were prepared via thermal evaporation of bulk Ge20Se70Sn10 glass. The films were then annealed between 503 and 703 K leading to the formation of Sn0.5Ge0.5Se and Ge4Se9 phases. For samples annealed at TA ≥ 653 K, Sn0.5Ge0.5Se phase decomposed to form Ge4Se9 phase. Based on the reflectance R(λ) and transmittance T(λ) studies, various optical constants such as the refractive index and extinction coefficient, real and imaginary of dielectric constants among others were investigated. Linear parameters such as the optical band gap decreased (~0.94 eV) as the annealing temperature increased while the Urbach energy reveals contrasting behavior. The oscillator energy and the dispersion energy decreased with increasing TA. Other electronic parameters such as the Penn gap, electronic polarizability, Fermi energy, VELF, and SELF functions are significantly influenced by TA.