Interface energies of Ga2O3 phases with the sapphire substrate and the phase-locked epitaxy of metastable structures explained†

Despite the extensive work carried out on the epitaxial growth of Ga₂O₃, a fundamental understanding of the nucleation of its different metastable phases is still lacking. Here we address the role of interface energies using density functional theory calculations of α, β and κ-Ga₂O₃ on (0001) Al₂O₃ substrates, and different Ga₂O₃ interlayers. In conjunction with surface energies and misfit strain contributions, we demonstrate that α-Ga₂O₃ is the preferred phase in 2D islands, when the low growth temperatures and the high growth rates hinder 3D island nucleation. This quantitatively explains the phase-locking in mist-CVD experiments.