First-principles study of p-type dopants in NiO

NiO is one of the few wide-bandgap oxides exhibiting p-type conductivity. However, the p-type conductivity is usually caused by an intrinsic defect: Ni vacancies. As such, the defect concentration and the associated hole concentrations are difficult to control. Moreover, oxygen vacancies can also form, especially under oxygen-poor conditions, and these will behave as compensating deep donors. Extrinsic doping is therefore required to fully control the p-type conductivity.

Using density functional theory (DFT) with hybrid functionals, we systematically screened potential p-type dopants for NiO, calculating formation energies and transition levels to evaluate their effectiveness and mitigate self-compensation. Our results identify alkali metals (Li, Na, K) as the most promising dopants, exhibiting low formation energies and producing shallow acceptor levels. This work provides quantitative design principles for engineering stable p-type conductivity in NiO-based devices.