Control of Hole Density in Russellite Bi₂WO₆ via Intentional Chemical Doping

Based on the fundamental design concept of modulatingthe valenceband maximum of oxides and subsequent predictions through computationalapproaches, several lone-pair ns (2)-basedp-type oxide semiconductors, such as Sn2+- or Bi3+-based complex oxides, have been developed. Thus far, the bandgapcan be modified via tuning of the chemical composition, whereas thehole density cannot be intentionally controlled because of the poorchemical stability of Sn2+ and/or the formation of oxygenvacancies. The inability to control hole density prohibits the designand realization of emergent electronic devices based on p- and n-typeoxide semiconductors. Herein, we report the control of hole densityvia intentional chemical doping in polycrystalline Bi2WO6. While the holes of polycrystalline Nb- or Ta-doped Bi2WO6 are strongly trapped by grain boundaries, thehole density obtained at high temperatures monotonically increaseswith the increase in the doping concentration. This study providesimportant insights into the development of practical p-type oxidesemiconductors. Thehole carrier density of Bi2WO6 can be controlledby the chemical doping of Nb5+ andTa(5+) into W6+ sites. By improvement of the crystallinityvia higher temperature synthesis, hole carrier density is significantlyimproved and close to an expectation from nominal compositions. Theseresults represent an advancement in the development of p-type oxidesemiconductors and their electric devices.