Sliding ferroelectricity in bilayer phosphorus analogue compounds: mechanisms and applications.

Two-dimensional (2D) van der Waals (vdW) ferroelectric structures have attracted much attention due to their superior properties and broad application prospects. For many systems, although there have been plenty of studies on monolayer ferroelectrics, bilayer or multilayer ferroelectricity has been rarely investigated. Here, we focus on the sliding ferroelectricity of bilayer α- and β-phase MX (M = Si, Ge, Sn and Pb; X = S, Se and Te) structures. Bilayer α-SiS is found to exhibit a quite large out-of-plane polarization that is not present in the monolayer configuration. Interestingly, the polarization of bilayer β-MX shows a periodic variation with the change of X atoms, where the charge transfer is found to play an important role. Furthermore, both strain and multilayer stacking are found to be able to effectively modulate the polarization. With those structures, field-effect transistors (FETs) are constructed, and their performances are found to satisfy the International Technology Roadmap for Semiconductors (ITRS) requirements for the year 2028. Moreover, four kinds of logic operators are proposed and also demonstrated to operate quite well, showing great application potential. We believe our findings will be quite beneficial for the development of sliding ferroelectrics.