Surface reconstructions on bare and hydrogenated beta-Ga2O3 surfaces: Implications for growth

Hydrogen is present during the growth of beta-Ga2O3 using chemical vapor deposition techniques. A detailed understanding of hydrogen-related surface reconstructions is therefore essential for controlling the material properties. We use density functional theory to explore the adsorption of hydrogen, gallium, and oxygen adatoms on the Ga2O3(010) and Ga2O3 (110) surfaces and generate a surface phase diagram, which shows surface reconstructions as a function of Ga and H chemical potentials. We find that the reconstructions on (110) and (010) surfaces are similar, due to the similarity in bonding. In the absence of hydrogen we find that the ideal unreconstructed surface is low in energy but that reconstructions with Ga and O adatoms can be favorable under more Ga-rich conditions. We question whether such "bare" surfaces can be experimentally observed, since hydrogen-related reconstructions are favored even at very low hydrogen pressures (consistent with residual gas pressures in ultrahigh-vacuum systems). Under more H-rich conditions, multiple hydrogen-containing reconstructions are found, with H adsorption being more stable under O-rich conditions. We find that the electron counting rule is valuable for assessing the stability of surface reconstructions. Knowledge of surface reconstructions and of the stability of hydrogen on the surface will help tailor growth conditions to achieve optimal layer quality.