Tailored Electronic Band Gap and Valance Band Edge of Nickel Oxide via p-Type Incorporation

A p-type semiconductor candidate of nickel oxide (NiO) desires longer carrier lifetimes with suitable conduction band edge, which holds a unique advantage to drive the hydrogen evolution toward efficient water splitting. However, a relatively large band gap (∼4 eV) greatly hinders its practical applications. We thus theoretically explore the band edge tailoring of NiO by doping electron-poor S on the sites of O. With the increase of incorporated S density, the electronic band gap ( E g ) of p-type-doped NiO is reduced with the improved valance band maximum (VBM), which is dominated by the emerged S 3p orbital hybridized with Ni t 2g states. Accordingly, the hole transportation might be enhanced due to the enlarged VBM offset between the active layer and NiO 1– x S x . Furthermore, the magnetic momentum per Ni atom increases with the increase of S densities, owing to the p-type-doping-induced majority and minority spin mismatch. It is confirmed that the VBM of NiO with S density lower than 2.08% consists of S 3p and Ni t 2g states with majority spin. Moreover, as a turning point, the special quasirandom structure (SQS) with S density as high as 2.78% shows a balanced spin feature, while the states with minority spin play a predominant role in the VBM with S density higher than 8.33%.