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

Abstract

A quasibinary system of Ga2O3-Al2O3 offers a range of applications in wide bandgap semiconductor engineering. Different polymorphs and concentrations of (AlxGa1-x)2O3 manifest a variety of structural and electronic properties, paving the way for tunability of (AlxGa1-x)2O3 for specific functions. In this work, we investigate the energetics of alpha (α) and beta (β) 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 (AlxGa1-x)2O3 configurations show an overlap at 50% concentration and a lowest energy configuration crossing at around 80% Al concentration. The lowest formation energy configurations for 50% concentration in both α and β 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.