First-principles calculations to investigate optoelectronic properties and pressure effect on thermodynamic parameters of the quaternary alloys Ga₁₋xSb₁₋yTlxBiy
摘要
The present study investigates the physical properties of Ga1-xSb1-yTlxBiy (x, y = 0, 0.25, 0.50, 0.75 and 1) using ab-initio approaches. The results of ground-state structural parameters show that the lattice constant increases with increasing Tl and Bi concentrations, while the bulk modulus exhibits a non-monotonic behavior, reflecting compositional effects on structural rigidity. The study of the electronic properties shows a strong dependence of the band gap on composition of Tl and Bi, with most of the investigated alloys exhibiting a narrow predominantly indirect band gap (E(Γ-X)). The density of states analysis indicates strong hybridization between cation (Ga, Tl) and anion (Sb, Bi) orbitals, confirming the covalent nature of bonding in these materials. The optical properties of Ga1-xSb1-yTlxBiy alloys were studied via the complex dielectric function. The imaginary part ε2 (ω) shows strong peaks in the 1–3 eV range due to interband transitions, indicating infrared absorption. The real part ε1 (ω) exhibits high static dielectric constants, while the refractive index shows large low-energy values, confirming strong electronic polarizability. Thermodynamically, the heat capacity Cv increases with temperature toward the Dulong–Petit limit and decreases slightly under pressure. Additionally, pressure is found to influence the magnitude and evolution of Cv, indicating modifications in phonon interactions. The Debye temperature increases with pressure but decreases with temperature, while entropy and enthalpy increase nonlinearly with temperature, reflecting anharmonic effects and pressure sensitivity of the studied alloys. These findings suggest that Ga1-xSb1-yTlxBiy alloys are promising materials for tunable infrared absorption and photodetection applications.