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

Bismuth oxyselenide (BiOSe) 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 BiOSe is still missing. Here, the helicity-dependent photocurrent (HDPC) was investigated in BiOSe nanosheets. By analyzing the dependence of HDPC on the angle of incidence, we find that the HDPC originates from surface states with symmetry in BiOSe, 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 BiOSe 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 BiOSe. The large HDPC in BiOSe nanosheets and its efficient electrical tuning demonstrate that 2D BiOSe nanosheets may provide a good platform for opto-spintronics devices.