First-principles study of Al substitution at Ga_(II)-site in β-Ga₂O₃: Enhanced mechanical strength and phonon-related thermal indicators for power electronics

Aluminum-doped β-gallium oxide (β-Ga₂O₃) is a promising ultrawide bandgap semiconductor for high-power applications due to its mechanical and thermal resilience. This study employs first-principles density functional theory (DFT) using the CASTEP code with the PBEsol functional to evaluate the structural, electronic, and mechanical properties of β-Ga2O3 fully substituted with Al at Ga(II) octahedral sites under hydrostatic pressures ranging from −5 to +5 GPa. The results reveal enhanced stiffness, with the bulk modulus increasing from 122.5 to 163.3 GPa and Young's modulus from 201.6 to 233.6 GPa. Electronic band structures, corrected using a 2 eV scissor operator, revealed a widening of the bandgap with increasing compressive pressure, reaching 5.15 eV at +5 GPa. Mulliken population analysis and charge density maps reveal stronger Al-O bonding and increased covalency compared to the replaced Ga(II)-O bonds. While direct thermal conductivity calculations were not performed, consistently high Debye temperatures (626–667 K) and bond stiffening suggest potential improvements in phonon-mediated heat transport; however, these trends are indicative rather than conclusive. The results highlight Ga(II)-specific Al substitution as a practical approach to enhancing mechanical robustness and tunable electronic properties in β-(Al_xGa_1-x)₂O₃ in high-voltage, thermomechanically robust power electronic devices.