Theoretical design of rhombohedral-stacked MoS2-based ferroelectric tunneling junctions with ultra-high tunneling electroresistances

Abstract

The sliding ferroelectrics formed by rhombohedral-stacked transition metal dichalcogenides (R-TMDs) greatly broaden the ferroelectric candidate materials. However, the weak ferroelectricity and many failure behaviors (such as irreversible lattice strains or defects) regulated by applied stimuli hinder their application. Here we systematically explore the interface electronic and transport properties of R-MoS₂-based van der Waals heterojunctions (vdWHJs) by first-principles calculations. We find that the polarization and the band non-degeneracy of 2R-MoS₂ increase with decreasing interlayer distance (d₁). Moreover, the polarization direction of graphene (Gra)/2R-MoS₂ P↑ state can be switched with a small increase in d₁ (about 0.124 Å) due to the weakening of the polarization field (E_p) by a built-in electric field (E_i). The equilibrium state of superposition (|E_p + E_i|) or weakening (|E_p − E_i|) can be modulated by interface distances, which prompts vertical strain-regulated polarization or Schottky barriers. Furthermore, Gra/2R-MoS₂ and Gra/R-MoS₂/WS₂ vdW ferroelectric tunneling junctions (FTJs) demonstrate ultra-high tunneling electroresistance (TER) ratios of 1.55 × 10⁵ and 2.61 × 10⁶, respectively, as the polarization direction switches. Our results provide an avenue for the design of future R-TMD vdW FTJs.