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

Bismuthoxyselenide (Bi2O2Se) is a two-dimensional(2D) layered semiconductor material with high electron Hall mobilityand excellent environmental stability as well as strong spin-orbitinteraction (SOI), which has attracted intense attention for applicationin spintronic and spin optoelectronic devices. However, a comprehensivestudy 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, wefind that the HDPC originates from surface states with C ( s ) symmetry in Bi2O2Se, which can be attributed to the circular photogalvanic effect(CPGE) and circular photon drag effect (CPDE). It is revealed thatthe HDPC current almost changes linearly with the source-drainvoltage. Furthermore, we demonstrate effective tuning of HDPC inBi(2)O(2)Se by ionic liquid gating, indicating thatthe spin splitting of the surface electronic structure is effectivelytuned. By analyzing the gate voltage dependence of HDPC, we can unambiguouslyidentify the surface polarity and the surface electronic structureof Bi2O2Se. The large HDPC in Bi2O2Se nanosheets and its efficient electrical tuning demonstratethat 2D Bi2O2Se nanosheets may provide a goodplatform for opto-spintronics devices.