Stacking-engineered polarization amplification and degenerate double-well in GaN-GeC heterostructures

Two-dimensional (2D) ferroelectrics are pivotal for next-generation ultra-low-power, high-density memory and logic devices, yet existing systems face critical bottlenecks: high switching barriers, insufficient polarization strength, and unstable out-of-plane polarization. The present work pioneers the theoretical design of bilayer/trilayer GaN-GeC van der Waals heterostructures and GaN-GeC/MoS 2 composites, demonstrating 2D sliding ferroelectrics with intrinsic out-of-plane polarization, high polarization strength (bilayer: 3.53–3.83 pC/m; trilayer: 8.55 pC/m) and ultralow switching energy consumption. Systematic investigations confirm their stable indirect bandgap semiconductor behavior and robust sliding ferroelectricity; trilayers achieve degeneracy-restored polarization via mirror-symmetric ABC/ACB stacking, with polarization 2.5× that of bilayers and exceeding most reported 2D ferroelectrics. Crucially, bilayers exhibit an ultralow polarization reversal barrier (9–19 meV) along lattice-diagonal paths, while trilayers enable stepwise switching via stable double-well intermediate state. A MoS 2 -supported GaN-GeC ferroelectric heterostructure is further investigated as a prototype precursor for future FTJ devices. The optimal MoS 2 /GaN stacking exhibits direct bandgaps of 0.394 eV (AB@U1) and 1.013 eV (AC@U1), yielding a pronounced inter-polarization band structure asymmetry of 0.619 eV. This asymmetry serves as a necessary precondition for tunneling electroresistance (TER) effects. However, we emphasize that quantitative TER evaluation awaits the future integration of metallic electrodes and quantum transport simulations; the present work focuses on structural and electronic screening of this van der Waals interface. This investigation establishes a novel paradigm for advanced 2D ferroelectric design, positioning GaN-GeC heterostructures as foundational components for post-silicon electronics.