Room-Temperature Ferroelectricity of Bi 2 O 2 Se in the Two-Dimensional Limit

Atomic-scale two-dimensional (2D) ferroelectrics are of great interest for advancing next-generation high-performance electronics. Here, we report the discovery of room-temperature (RT) ferroelectricity in ultrathin 2D Bi 2 O 2 Se (BOS) films grown by molecular beam epitaxy. These films exhibit degenerate semiconducting characteristics through a unique self-modulated doping mechanism featuring in-plane electron confinement and a high RT mobility of 311 cm 2 V –1 s –1 . Remarkably, robust out-of-plane ferroelectricity persists down to the single-unit-cell limit. Through atomic-scale characterization, we reveal that the ferroelectric polarization stems from electric-field-modulated dipole ordering associated with Se atom displacements. This study confirms the ferroelectricity of ultrathin BOS films, thereby opening new avenues for the development of innovative nanoscale devices and the engineering of quantum materials.