Doping of Ga2O3 with transition metals

We explore the viability of using transition-metal impurities as n-type dopants in beta-Ga2O3, focusing on W, Mo, Re, and Nb. Our first-principles calculations show that these impurities can incorporate on both crystallographically inequivalent Ga sites, with the octahedrally coordinated sites being preferred. Mo and Re behave as deep donors. Tungsten on a tetrahedral site is a shallow donor, but unfortunately W on an octahedral site is much lower in energy. Niobium emerges as the best candidate for n-type doping: It has a low formation energy, is a shallow donor on the tetrahedral site, and has only a modest ionization energy (0.15 eV) on the octahedral site.