Wurtzite BeX (X = S, Se, Te) Monolayers and Heterostructures with Pure Out-of-Plane Spin-Polarization for Non-Volatile Spintronic Devices

The development of semiconductors with pure out-of-plane (OOP) spin polarization, which features electrically switchable spin splitting and a strong response to electric fields, is crucial for manipulating high-density perpendicular magnetic memories and logic devices without an external magnetic field. However, conventional Rashba splitting arises from broken OOP inversion symmetry, which produces only in-plane (IP) spin polarization. Here, we demonstrate that an OOP spin polarization at the valence band maximum (VBM) can be activated in nanoscale thickness wurtzite (wz) monolayers of BeX (X = S, Se, Te) and in their heterostructures. The spin splitting can be reversibly switched by flipping the IP ferroelectric polarization. Notably, these wz monolayers exhibit a large Rashba coefficient (2.22–2.49 eV Å), strong spontaneous electric polarization, and low switching energy barriers, enabling room-temperature device operation at the nanoscale. Using wz monolayers as building blocks, we find that both OOP spin polarization and IP Rashba spin-splitting can occur at the VBM and the conduction band maximum (CBM) in the corresponding heterostructures. Additionally, the monolayers can be integrated with graphene or h -BN to form heterostructures while retaining their intrinsic spin-splitting characteristics. Finally, we propose integrated spin-Hall designs based on the BeTe monolayer and the Be 2 STe heterostructure, which exhibit ultrashort channel lengths of 0.54 and 0.92 nm, respectively, highlighting their potential for nanoscale device integration. Our work establishes a useful framework for designing efficient all-electric, nonvolatile spintronic devices such as spin-Hall devices based on atomically thin wz semiconductors with purely OOP spin polarization.