Electric Control of Helicity-Dependent Photocurrent and Surface Polarity Detection on Two-Dimensional Bi₂O₂Se...

Bismuth oxyselenide (Bi₂O₂Se) is a two-dimensional (2D) layered semiconductor material with high electron Hall mobility and excellent environmental stability as well as strong spin-orbit interaction (SOI), which has attracted intense attention for application in spintronic and spin optoelectronic devices. However, a comprehensive study of spin photocurrent and its microscopic origin in Bi₂O₂Se is still missing. Here, the helicity-dependent photocurrent (HDPC) was investigated in Bi₂O₂Se nanosheets. By analyzing the dependence of HDPC on the angle of incidence, we find that the HDPC originates from surface states with C symmetry in Bi₂O₂Se, which can be attributed to the circular photogalvanic effect (CPGE) and circular photon drag effect (CPDE). It is revealed that the HDPC current almost changes linearly with the source-drain voltage. Furthermore, we demonstrate effective tuning of HDPC in Bi₂O₂Se by ionic liquid gating, indicating that the spin splitting of the surface electronic structure is effectively tuned. By analyzing the gate voltage dependence of HDPC, we can unambiguously identify the surface polarity and the surface electronic structure of Bi₂O₂Se. The large HDPC in Bi₂O₂Se nanosheets and its efficient electrical tuning demonstrate that 2D Bi₂O₂Se nanosheets may provide a good platform for opto-spintronics devices.