Comprehensive first-principles study of group IIIA-VIA A₂B₃ two-dimensional ferroelectrics

Two-dimensional (2D) ferroelectric materials, particularly α-A₂B₃-type compounds, have attracted significant attention due to their intrinsic out-of-plane polarization and potential applications in nonvolatile memory and ferroelectric tunnel junctions. However, a comprehensive database of key physical parameters, especially surface energy levels that govern interfacial band alignment, remains lacking, hindering rational device design. In this work, we systematically investigate the structural stability and electronic properties of 16 α-A₂B₃ monolayers (A = B, Al, Ga, In; B = O, S, Se, Te) using first-principles calculations. We find that boron-containing compounds are dynamically unstable and adopt a nonpolar structure instead, excluding them from out-of-plane ferroelectric applications. For all stable systems, we provide a parameter library including lattice constants, band gaps, work functions, polarization intensities, switching barriers, and, most critically, the VBM/CBM energy offsets relative to vacuum for both surfaces. With these data, the initial band alignment between any A₂B₃ monolayer and another material can be directly determined by aligning their vacuum levels, enabling rapid prediction of charge transfer and insulator-metal transitions. This work offers a ready-to-use database for designing ferroelectric heterostructures and related devices.