Thermodynamic phase stability, structural, mechanical, optoelectronic, and thermoelectric properties of the III-V semiconductor AlSb for energy conversion applications

• DFT calculations performed for AlSb in cubic and hexagonal phases. • Phonon spectra show no imaginary frequencies, confirming full dynamic stability. • Band gaps: 1.66 eV (HSE06) and 1.72 eV (mBJ) for cubic, slightly smaller for hexagonal. • Strong optical absorption (10 6 cm -1 ) and high refractive index (n max ≈ 5.4). • Seebeck coefficients reach ≈ 1550 µV/K @ 300 K, indicating good thermoelectric efficiency. This study presents a first-principles investigation of the structural, thermodynamic, electronic, optical, and thermoelectric properties of aluminum antimonide (AlSb) in its cubic (F-43 m) and hexagonal (P6 3 mc) phases. Both structures are dynamically and mechanically stable, which is confirmed by phonon calculations and the Born-Huang criteria. The lattice constants obtained using the SCAN and PBEsol functionals show good agreement with experimental data. The cubic phase has a direct band gap of 1.66–1.78 eV, while the hexagonal phase has 1.48–1.59 eV, as confirmed by mBJ and HSE06 calculations. Under external pressure, the band gap decreases in the cubic phase and increases in the hexagonal phase due to different s-p orbital hybridization mechanisms. The optical absorption coefficient reaches 10 6 cm -1 , which is comparable to or higher than values known for other III–V semiconductors. The Seebeck coefficient exceeds 1500 µV/K under intrinsic conditions, and the thermoelectric performance improves above 600 K due to enhanced phonon scattering and lattice anharmonicity. The calculated formation energies (-1.316 eV for F-43 m and -1.258 eV for P6 3 mc) confirm that the cubic phase is thermodynamically more stable. The hexagonal phase shows higher anisotropy and lower lattice stiffness, which is beneficial for thermoelectric applications. These results demonstrate how crystal symmetry, phonon behavior, and charge transport are connected, and they provide useful guidance for the design of AlSb-based materials for optoelectronic and energy-conversion technologies.