The results of a theoretical study of the point defects of monoclinic β-Ga2O3 were reported. The point defects considered were vacancies and interstitials, together with dopant ions such as Be, Mg, In, Cr, Si, Ge, Sn and Zr. Since the low symmetry of the monoclinic lattice did not provide an unambiguous location for interstitial sites and migration paths, an unique means was proposed for their identification in terms of the electron density topology. Special attention was given to the preference, among lattice and interstitial sites, for impurity defects, and to its explanation in terms of structural, electrostatic and electron density arguments. The calculated results showed that the most prominent features in the lattice were the existence of empty channels along the b direction and atomic layers perpendicular to them. Their interplay governed the stability and mobility of point defects in β-Ga2O3. The anionic Frenkel pair, consisting of an O vacancy and an O interstitial, was predicted to dominate the defect structure in the lattice. The dopants considered were likely to be stabilized at the octahedral Ga sites, except for Be2+; which preferred to occupy a tetrahedral Ga site in the lattice. Some of the possible migration paths were determined, and the pseudo-activation energies for the intrinsic, O-rich, and O-deficient conditions were computed as a function of temperature. It was suggested that tuning the concentration of O could lead to a change in the anisotropy of the ionic conductivity in β-Ga2O3.

Energetics and Migration of Point Defects in Ga2O3. M.A.Blanco, M.B.Sahariah, H.Jiang, A.Costales, R.Pandey: Physical Review B, 2005, 72[18], 184103 (16pp)