Control of Hole Density in Russellite Bi₂WO₆ via Intentional Chemical Doping

Based on the fundamental design concept of modulating the valence band maximum of oxides and subsequent predictions through computational approaches, several lone-pair ns²-based p-type oxide semiconductors, such as Sn²⁺- or Bi³⁺-based complex oxides, have been developed. Thus far, the bandgap can be modified via tuning of the chemical composition, whereas the hole density cannot be intentionally controlled because of the poor chemical stability of Sn²⁺ and/or the formation of oxygen vacancies. The inability to control hole density prohibits the design and realization of emergent electronic devices based on p- and n-type oxide semiconductors. Herein, we report the control of hole density via intentional chemical doping in polycrystalline Bi₂WO₆. While the holes of polycrystalline Nb- or Ta-doped Bi₂WO₆ are strongly trapped by grain boundaries, the hole density obtained at high temperatures monotonically increases with the increase in the doping concentration. This study provides important insights into the development of practical p-type oxide semiconductors.