Room‐Temperature Ferroelectricity in Ultra‐Thin p‐Type BiCuSeO Films

Atomically thin 2D layered ferroelectric semiconductors, where polarization switching transpires within the channel material itself, are pivotal to advancing the next generation of high-performance electronics. Nevertheless, the challenge remains in either the controllable synthesis of films or the manipulation of associated ferroelectricity. Here, 2D p-type BiCuSeO (BCSO) films with a thickness down to ≈3 nm are successfully synthesized using molecular beam epitaxy. The room-temperature (RT) out-of-plane ferroelectricity is confirmed by piezoelectric force microscopy, showing robust ferroelectric switching capability. Insights derived from density functional theory, coupled with the ferroelectric dipole map in cross-sectional scanning transmission electron microscopy images, suggest that the polar displacement of [CuSe] layers under electric fields primarily contributes to ferroelectricity in the BCSO film. Furthermore, the switching behavior of the BCSO-based ferroelectric tunnel junction has been clarified, exhibiting distinct ON and OFF states. Our results illustrate that such an ultrathin RT ferroelectric semiconductor could serve as a versatile material for future multifunctional electronic devices.