Metastable cation vacancies in semiconducting oxides

Theoretical and experimental evidence has emerged [1] over the past decade that the simple cation vacancy in a number of semiconducting oxides is metastable, and that the lowest-energy configuration may have the form of cation vacancy – cation interstitial – cation vacancy. This situation may occur in crystal structures for which such a configuration has high symmetry and in which the cation interstitial forms tetrahedral or octahedral bonds with adjacent oxygens. Such structures include the Ga(1) vacancy in the β phase of Ga₂O₃, the cation vacancy in the α phase of Ga₂O₃, Al₂O₃ and In₂O₃, and the Cu vacancy in Cu₂O, among others. We review and (using the CRYSTAL17 code [2]) add to the existing knowledge of this family of defects, and note that it is critical that the significance of the “shifted” structure as the equilibrium configuration be fully recognized in calculations of electronic properties, level positions, and other properties for these and similar systems.

[1] See A. Venzie et al., Appl. Phys. Lett. 120, 192101 (2022) for a collection of relevant references.

[2] R. Dovesi et al., WIREs Comput. Mol. Sci., e1360 (2018).