Impact of Se and Te addition on optical characteristics of ternary GeInSb chalcogenide films as promising materials for optoelectronic applications

The present study investigates the linear and non-linear optical characteristics of non-crystalline quaternary Ge15In5Sb5Se75 (GIS-Se) and Ge15In5Sb5Te75 (GIS-Te) chalcogenide thin films. The amorphous nature of the studied compositions was confirmed by x-ray diffraction (XRD). The values of transformation temperatures determined by differential thermal analysis (DTA), such as glass transition T-g and crystallization T-c temperatures, are 524.3 and 639.6 K for GIS-Se and 503.6 and 542.0 K for GIS-Te. The calculated values of glass forming ability (GFA) and thermal stability (H) for GIS-Se are higher than those for GIS-Te. The transmittance T(lambda) and reflectance R (lambda) spectrophotometric measurements in the UV-vis. wavelength range (400-2500 nm) are used to estimate the index of refraction n and extinction coefficient k. The obtained values of n and k are found to be thickness independent in the investigated range. Tauc's extrapolation model was used to determine both Urbach tail (E-U) and optical band gap (E-g(opt)) energies. The values of (E-U) are 0.416, 0.526 eV and (E-g(opt)) are 1.83, 1.31 eV with indirect allowed transitions for GIS-Se and GIS-Te, respectively. The optical conductivity sigma(opt) increased as photon energy (h nu) increased, and it was enhanced in the presence of Te than Se addition. The analysis of the index of refraction (n) is used to evaluate the dispersion energy E-d, the high frequency dielectric constant epsilon(infinity), the oscillator strength S-0, the lattice dielectric constant epsilon(L), the ratio N/m* and the optical electronegativity empty set(opt), which were found to be higher in GIS-Te than those in GIS-Se composition. The volume (VELF) and surface (SELF) energy loss functions were found to be increased with increasing (h nu) and the presence of Te. Furthermore, the calculated values of nonlinear optical susceptibility chi((3)) and nonlinear index of refraction n(2) for GIS-Se and GIS-Te are 0.195 x 10(-12), 2.44 x 10(-11) esu and 0.868 x 10(-12), 10.19 x 10(-11) esu, respectively. The detailed outcomes show that the studied film samples are suitable for various optical applications such as phase-change optical rewritable disks, optical sensors, optoelectronic devices and high-speed optical fibers.