Surface and volume energies of -, -, and -Ga₂O₃ under epitaxial strain induced by a sapphire substrate

In order to understand the competition among alpha, beta, and kappa phases in Ga2O3 deposition on sapphire substrates, particularly the easy appearance of the orthorhombic kappa phase in MOCVD experiments, we calculated the volume and the surface energies under misfit strain relative to the experimental orientations of the three phases. This applies to the early stages of growth, indicating that the energetic advantage of the beta-(-201) film is no longer present on the sapphire substrate. In optimizing the atomistic structure of the strained surfaces, we also discovered a very effective and intriguing reconstruction of the kappa phase for the (001) and (00-1) surfaces, which is the lowest in energy among the low-Miller indexes surfaces of this phase, even at zero strain.