Sliding Ferroelectricity Induced Spatio-Segregation of Band-Edge Carriers in Bilayer HfN ₂

Sliding ferroelectricity produces switchable out-of-plane polarization in 2D homobilayers. However, whether this polarization can segregate the spatial distribution of electrons and holes at the band edges, and which material properties control this behavior, remain open questions. Using first-principles calculations, we show that homobilayer HfN 2 is a sliding ferroelectric with an ultralow switching barrier of 27 meV/fu. Sliding-induced symmetry breaking produces a 95 meV vacuum-level asymmetry between its two surfaces. We observe a reversible spatially segregated band-edge carriers, a functionality previously observed in type-II heterobilayers but realized here within a homobilayer. A two-level tight-binding model is developed to identify the orbital origin of this band-edge segregation, and its validity is demonstrated through comparison with a bilayer transistion metal dichalcogenide system. These results establish an orbital design principle for identifying homobilayers where sliding-induced ferroelectricity can controllably separate band-edge carriers, opening a pathway toward sliding-controlled optoelectronic and photovoltaic functionalities in atomically thin materials.