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.