Sliding ferroelectricity in two-dimensional MoA2N4 (A = Si or Ge) bilayers: high polarizations and Moiré potentials

Abstract

According to the model of sliding ferroelectricity we proposed in 2017, a type of vertical polarization 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 these properties may render the long-sought and efficient computing-in-memory possible. Their high polarizations induce strong Moiré 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 gives rise to a high alternating voltage when used as a nanogenerator, suggesting promising potential for energy harvesting.