Stusy of the Fundamental Properties of II-VI and III-V Semiconductor in the Framework of the DFT

Abstract

This thesis presents a first‑principles study of structural, stability, electronic, optical, elastic and thermal properties for four ternary alloys, the zinc-blende AlSb1−xAsx, AlSb1−xBix, and the rock‑ salt BaO1−xSx and BaO1−xSex at x = 0, 0.25, 0.50, 0.75, and 1. Energy-Volume data were fitted to Murnaghan E(V) establishing zinc‑blende and NaCl as the most stable phases. The enthalpy versus pressure study provides quantitative insight into the critical pressures associated with the phase transitions. The band structure and DOS calculations were carried out using the mBJ potential developed by Koller, Tran, and Blaha. AlSb1−xAsx ternary alloys exhibit a direct band gap Γ–Γ at x = 0.25 – 0.75. AlSb1−xBix have direct band gaps for all compositions with a nonzero concentration, the band gap decreases and extends from the near-infrared to the mid-infrared spectral range.The elastic constants were obtained using WC GGA/IRElast and Voigt-Reuss-Hill approaches. The optical spectra include the real and imaginary parts of the dielectric function, the refractive index, the absorption coefficient, and the reflectivity was investigated and discussed in detail. Thermal properties obtained from the Debye model reveal consistent trends linking atomic mass, chemical bonding, and lattice stiffness. Heat capacity shows the expected low-temperature rise and hightemperature saturation, the Debye temperature tracks lattice rigidity, the bulk modulus decreases with temperature, and the thermal expansion increases with temperature. The sodium chloride to cesium chloride transition pressures decrease with increasing chalcogen content and approach reported binary limits. Agreement with theoretical and experimental data for the binaries, together with consistency across properties, validates the used approaches. The thesis delivers a dataset of material properties across the compositions ( x). With newly reported elastic, optical, and thermal properties for compositions (x= 0.25, 0.5 and 0.75),in addition to identifying potential applications of these compounds, including light-emitting devices and photodetectors, as well as coatings and near-ultraviolet sensing devices