The main role of bismuth in controlling linear and nonlinear optical, electronic and electrical parameters of Se–Ge–Bi thin films

A widespread analysis of the structural, optical, electronic and electrical properties of Se₈₀Ge_20-xBi_x with (x = 0, 5, 10, 15 and 20 at.%) glasses were carried out. The bulk materials of the studied films have been prepared utilizing the usual melt quench procedure. Thus, the thin film has been deposited under a vacuum of 10^–5 Torr on cleaned glass substrates by thermal evaporation. The supreme purpose of this research is to highlight the role of adding bismuth to the films studied as a regulator and controller for the linear and nonlinear parameters. The thickness of the studied thin films has been mathematically determined by the methods of Swanepoel. Using logarithmic functions, it has been proven that the electron transport mechanism between the valence and conduction bands is an allowed indirect transition. Linear optical parameters, dielectric constants and also dispersion parameters have been calculated. The energy-loss functions (VELF and SELF) were discussed. The effect of Bi concentration in the studied thin films on the linear and nonlinear optical properties is determined based on the optical measurements (transmittance and reflectance spectra). The optical bandgap decreases with increasing Bi concentration; while the tail energy portrays an opposite behavior. Linear optical and electrical parameters are found significantly affected by the change of Bi concentration. In contrast, the nonlinear optical parameters have been computed utilizing (H. Ticha and L. Tichy) and Boling formula. Energies of Plasmon, Penn and Fermi and the electronic polarizability have been determined. Furthermore, the DC electrical conductivity has been studied as a function of both temperature in the thermal range from 300 to 500 K and also Bi concentration. In the extended and hopping regions, the activation energy and pre-exponential factor were extracted from the slopes and intercepts of straight lines. It has been found that increasing Bi content is controlled the electrical parameters and reduces the activation energies in the regions of the extended and the hopping states.