Adsorption and Diffusion of Aluminum on β-Ga₂O₃(010) Surfaces

Epitaxial growth of aluminum gallium oxide is important for forming heterojunctions on Ga₂O₃ for high power electronics applications. We use density functional theory to explore the co-adsorption of Al, Ga, and O adatoms on the Ga₂O₃(010) surface and the surface reconstructions during the growth of the alloy. We find that Al can adsorb in tetrahedral sites in many of the reconstructions. The migration barrier escaping from a tetrahedral site to an octahedral site is 1.72 eV for an Al adatom and 0.56 eV for a Ga adatom, indicating that Al diffusion is much more restricted than Ga diffusion on the surface. Our findings indicate that kinetic limitations are responsible for Al occupying both octahedral and tetrahedral sites in (AlGa_1-)₂O₃, in spite of the fact that thermodynamically the octahedral site is preferred.