Deep acceptors and their diffusion in Ga2O3
β-Ga2O3 is a wide-bandgap material with promising applications in high-power electronics. While n-type doping is straightforward, p-type doping is elusive, with only deep acceptors available. We explore the properties of these acceptors, from the point of view of achieving stable semi-insulating layers, which are essential in many device structures. Using hybrid density functional theory, we obtain the comprehensive first-principles results for a variety of deep-acceptor impurities in Ga2O3. Among the impurities examined, nitrogen on an oxygen site and magnesium on a gallium site have particularly low formation energies, making them prime candidates for acceptor doping. Closer inspection of various configurations shows that Mg can incorporate not only on Ga sites (where it acts as a deep acceptor under n-type conditions) but also on O sites, where it acts as a deep donor. Mg interstitials adopt a split-interstitial configuration, sharing a site with a host Ga atom. Similarly, N substituting on an O site acts as a compensating center, but N can also incorporate on the Ga site. We evaluate the diffusivities of these species in the crystal by calculating migration barriers and considering which native defects assist in diffusion. We find that diffusion of N is dominantly assisted by O vacancies, while Mg diffusion is assisted by gallium interstitials. Diffusion of Mg proceeds with significantly lower activation energies than diffusion of N. Our results can be used to assess activation energies and diffusion mechanisms for other impurities in Ga2O3.
APL Materials, Volume 7, Issue 2, id.022519, 2019