High Tunneling Electroresistance in Ferroelectric Tunnel Junctions Based on 2-D Bilayer Ferroelectric CuInP₂Se₆/Ga₂O₃ van der Waals Heterostructure

Giant tunneling electroresistance (TER) has been realized via manipulating the electric polarization direction of the ferroelectric material in van der Waals heterostructure (vdWH) ferroelectric tunnel junctions (FTJs) where the vdWH is constructed by combining a ferroelectric material with a nonferroelectric material. In this work, we propose a new FTJ model by employing bilayer ferroelectric vdWH composed of two out-of-plane polarized ferroelectric materials. The 2-D ferroelectric materials CuInP2Se6 and Ga2O3, which both have two opposite polarization states P $\uparrow $ and P $\downarrow $ , are selected as an example to form the bilayer ferroelectric vdWHs and the corresponding FTJs to validate our model. The energy bands of P $\uparrow \uparrow $ state of the vdWH indicate an insulating state with a bandgap of 0.634 eV, while that of the P $\downarrow \downarrow $ state is zero, resulting in a metallic behavior, so a robust ferroelectric polarization-controlled switch behavior between the high conductance state in P $\downarrow \downarrow $ state and the low conductance state in P $\uparrow \uparrow $ state in CuInP2Se6/Ga2O3 vdWH is obtained. Then, based on this vdWH, a 2-D transverse FTJ with P $\uparrow \uparrow $ or P $\downarrow \downarrow $ state’s vdWH as the tunneling barrier and (Ga0.75Sn0.25)2O3 monolayer (exhibiting n-type doping) as electrodes is designed. The TER ratio as high as 106% can be achieved in the FTJ. An analysis via the work function model, charge redistribution, and local density of state (LDOS) is performed to analyze the above phenomena. Our work provides a feasible method to design high-performance FTJs with 2-D bilayer ferroelectric vdWHs and suggests the great potential of specific CuInP2Se6/Ga2O3 vdWH in the design of high-performance FTJs and the application in high-density nonvolatile memory devices.