Tailored Electronic Band Gap and Valance Band Edge of Nickel Oxide via p-Type Incorporation
Gang Wang, Jinju Zheng, Boyi Xu, Zhang Chaonan, Yue Zhu, Zhi Fang, Zuobao Yang, Minghui Shang, Weiyou Yang
Abstract
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 (Eg) 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 t2g states. Accordingly, the hole transportation might be enhanced due to the enlarged VBM offset between the active layer and NiO1–xSx. 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 t2g 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%.