Impact of transition metal doping on the optical characteristics of Se–Te thin film

Abstract

The optical properties of Se_80−xTe₂₀TM_x thin films (Where, TM = Fe, Co, Ni, Cu, and x = 0 or 2) were studied for their compositional dependence. Binary and ternary thin films were deposited onto preheated glass substrates using the thermal evaporation method under high vacuum conditions (~ 10⁻⁶ Torr). Through the collection of observational spectral data for both reflectance and transmittance across 200–2500 nm using an Ultraviolet (UV)—spectrophotometer, we evaluated the optical properties of the prepared thin films. Distinct samples exhibited unique optical characteristics. The optical absorption coefficient (α), refractive index (n), and extinction coefficient (k) were determined from the transmission (T(λ)) and absorption measurements. The analysis includes various linear optical parameters, such as the refractive index, extinction coefficient, real and imaginary parts of the dielectric constant, and loss tangent, all discussed with wavelength. The optical band gap \({(E}_{g}^{opt})\) and Urbach tail \({(E}_{u})\) have been determined through the analysis of the spectral variation in the dispersion characteristics. This calculation provides critical insight into the electronic structure and disorder within the material. The current samples exhibit the indirect optical transition, which is confirmed by the transition power factor m. Using the theoretical Wemple-DiDomenico model, we calculated the static refractive index (n), oscillator energy (E₀), and dispersion energy (E_d). The refractive index dispersion data adhered to the single oscillator model, which facilitated the determination of the dispersion parameters and the high-frequency dielectric constant. Further, the nonlinear characteristics of the samples are evaluated through their susceptibility and nonlinear refractive index.