Significantly enhanced tunneling electroresistance in two-dimensional ferroelectric tunnel junctions realized by reversible Schottky-Ohmic contact switching

Achieving large tunneling electroresistance (TER) is the key to the application of two-dimensional (2D) ferroelectric tunnel junctions (FTJs) in high-density memory devices. In this work, we show that an aided layer of 2D metal materials with ultrahigh work function can lead to significantly enhanced TER effect in 2D FTJs. To implement the idea, we design a 2D van der Waals heterostructure consisting of a metallic ${\mathrm{NbS}}_{2}$ monolayer and a ${\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$ ferroelectric, and propose a FTJ based on this heterostructure. By performing density functional theory and nonequilibrium Green's function method calculations, we find that the type of interfacial contact in the ${\mathrm{NbS}}_{2}/{\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$ heterostructure can be flexibly switched between Ohmic and Schottky contact by altering the ferroelectric polarization. Accordingly, the ${\mathrm{NbS}}_{2}/{\mathrm{Sc}}_{2}{\mathrm{CO}}_{2}$-based FTJ exhibit giant TER ratio of up to ${10}^{13}%$, and its TER ratio increases with the tunneling barrier length. These findings not only provide a feasible strategy for realizing large TER effect in 2D FTJs, but also offer promising candidates to designing nonvolatile memories.