Doping properties of monoclinic BiVO4 studied by first-principles density-functional theory

The intrinsic and extrinsic doping properties of BiVO4, i.e., the formation energies and transition energy levels of defects and impurities, have been studied systematically by first-principles density-functional theory. We find that for doping caused by intrinsic defects, Ovacancies are shallow donors and Bi vacancies are shallow acceptors. However, these defects compensate each other and can only lead to moderate n-type and p-type conductivities at Bi-rich and O-rich growth conditions, respectively. To obtain BiVO4 with high n-type and p-type conductivities, which are required for forming Ohmic contacts, extrinsic doping using foreign impurities is necessary. Our results reveal that Sr, Ca, Na, and K atoms on Bi sites are very shallow acceptors and have rather low formation energies. The calculated Fermi-level pinning positions predict that doping of these impurities under oxygen-rich growth conditions should result in outstanding p-type conductivity. Substitutional Mo and W atoms on V sites are very shallow donors and have very low formation energies. Fermi-level pinning position calculations expect the doping of Mo and W under oxygen-poor growth conditions to produce excellent n-type conductivity. Also discussed is the dependence of formation energies and transition energies of defects on the atomic size and atomic chemical potential trends.