Gallium vacancies in β-Ga2O3 crystals

The gallium vacancy, an intrinsic acceptor, is identified in β-Ga2O3 using electron paramagnetic resonance (EPR). Spectra from doubly ionized (VGa2−) and singly ionized (VGa−) gallium vacancies are observed at room temperature, without photoexcitation, after an irradiation with high-energy neutrons. The VGa2− centers (with S = 1/2) have a slight angular variation due to a small anisotropy in the g matrix (principal values are 2.0034, 2.0097, and 2.0322). The VGa2− centers also exhibit a resolved hyperfine structure due to equal and nearly isotropic interactions with the 69,71Ga nuclei at two Ga sites (the hyperfine parameters are 1.28 and 1.63 mT for the 69Ga and 71Ga nuclei, respectively, when the field is along the a direction). Based on these g-matrix and hyperfine results, the model for the ground state of the doubly ionized vacancy (VGa2−) has a hole localized on one threefold-coordinated oxygen ion. The vacancy is located at one of the three neighboring gallium sites, and the remaining two gallium neighbors are responsible for the equal hyperfine interactions. The singly ionized (VGa−) gallium vacancies are also paramagnetic. In this latter acceptor, the two holes are localized on separate oxygen ions adjacent to one gallium vacancy. Their spins align parallel to give a triplet S = 1 EPR spectrum with resolved hyperfine structure from interactions with gallium neighbors.