Sliding Ferroelectricity in Two-Dimensional MoA2N4 (A=Si or Ge) Bilayers: High Polarizations and Moire Potentials

According to the model of sliding ferroelectricity we proposed in 2017, a type of vertical polarizations switchable via interlayer sliding may exist in a series of two-dimensional van der Waals bilayers and multilayers. Such intriguing ferroelectricity has been recently experimentally confirmed in BN and WTe2 bilayer/multilayer systems. However, they are respectively insulators and metals with weak polarizations. Here we search for a combination of high-mobility semiconductors and ferroelectricity with relatively high polarizations, and we note that MoSi2N4 monolayer has been recently fabricated to centimeter scale based on MoN2 monolayer (Science 2020, 369, 670). We show first-principles evidence of strong interlayer sliding ferroelectricity in high-mobility semiconducting MoA2N4 (A=Si or Ge) bilayers and multilayers. They possess tunable bandgaps within the desirable range for nanoelectronics, with the current highest polarizations in sliding ferroelectrics known to date due to strong interlayer van der Waals interactions. Such a successful combination of those properties may render the long-sought and efficient computing-in-memory possible. Their high polarizations induce a strong Moire potential and unique band alignments for exciton trapping in twisted MoA2N4 bilayer. The varying charge distribution of different stacking in MoN2/MoSi2N4 hetero-bilayer also give rises to a high alternating voltage when used as a nanogenerator, suggesting promising potentials for energy harvesting.