Formation energy crossings in Ga₂O₃-Al₂O₃ quasibinary system: ordered structures and phase transitions in (Al _x Ga_1-x )₂O₃

A quasibinary system of Ga2O3-Al2O3 offers a range of applications in wide bandgap semiconductor engineering. Different polymorphs and concentrations of (Al (x) Ga1-x )(2)O-3 manifest a variety of structural and electronic properties, paving the way for tunability of (Al (x) Ga1-x )(2)O-3 for specific functions. In this work, we investigate the energetics of alpha (alpha) and beta (beta) polymorphs of Ga2O3 and Al2O3 by considering all possible configurations in a conventional unit cell. Using density functional theory, we show that the formation energies of (Al (x) Ga1-x )(2)O-3 in alpha and beta configurations start to coincide at 50% concentration (Al0.5Ga0.5)(2)O-3. The corundum configuration then becomes more dominant (lower in energy) than its monoclinic counterpart at around 80% Al concentration. The lowest formation energy configurations for 50% concentration in both alpha and beta polymorphs also manifest a preference towards an ordered phase. These show that the stability of Ga2O3-Al2O3 and its phase transitions are significantly influenced by the relative arrangements of Ga and Al within the quasibinary semiconducting crystal.