Energetics and migration of point defects inGa2O3

The results of a theoretical study on the point defects of monoclinic $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ are reported here. The point defects considered here are vacancies, interstitials together with dopant ions such as Be, Mg, In, Cr, Si, Ge, Sn, and Zr. Since the low symmetry of the monoclinic lattice does not provide an unambiguous location of interstitial sites and migration paths, we propose a unique way for their identification in terms of the electron density topology. Special attention has also been given to the preference among the lattice and interstitial sites for the impurity defects, and its explanation in terms of structural, electrostatic, and electron density arguments. The calculated results find the most prominent features in the lattice to be the existence of (i) empty channels along the $\mathbf{b}$ direction, and (ii) atomic layers perpendicular to them. Their interplay governs the stability and mobility of the point defects in $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$. The anionic Frenkel pair consisting of the oxygen vacancy and oxygen interstitial is predicted to dominate the defect structure in the lattice. The dopants considered here are likely to be stabilized at the octahedral gallium sites, except for ${\mathrm{Be}}^{+2}$, which prefers a tetrahedral gallium site in the lattice. Some of the possible migration paths have been determined, and the pseudoactivation energies for the intrinsic, oxygen-rich, and oxygen-deficient conditions are computed as a function of temperature. It is suggested that tuning the concentration of oxygen can lead to a change in the anisotropy of the ionic conductivity in $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$.