Giant tunnel electroresistance in ferroelectric tunnel junctions with metal contacts to two-dimensional ferroelectric materials

Two-dimensional (2D) ferroelectric materials (FEMs) and their application in ferroelectric tunnel junctions (FTJs) have attracted a great deal of attention during the past several years due to their great potential in nonvolatile memory devices. Particularly, the all-2D FTJs, which have only atomic-layer thickness, have been demonstrated to show very high tunnel electroresistance (TER) ratio. Nevertheless, to better integrate with the present semiconductor technology, it is necessary to consider metal contacts in the construction of FTJs with 2D FEMs. However, due to the unknown interaction between traditional metals and 2D FEMs, it is not clear whether ferroelectricity still persists when the 2D FEMS are in contact with metals and whether the corresponding FTJs exhibit high TER effect as demanded for memory devices. To probe this, we construct FTJs with top contact between Au(010) and ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$, a 2D FEM with out-of-plane ferroelectric polarization. By density functional calculations combined with a nonequilibrium Green function technique, we find that not only the ferroelectricity still persists in the metal/FEM contact, but also a giant TER ratio as high as ${10}^{4}%$ is achieved. The giant TER arises from the change of the metal/FEM contact from a Schottky type to an Ohmic type accompanying with the ferroelectric polarization reversal. In the meantime, the tunnel barrier height between Au(010) and ${\mathrm{In}}_{2}{\mathrm{Se}}_{3}$ is zero, which means good ability of electron injection from metal to semiconductor and low contact resistance. Our study suggests that, by properly selecting the metal materials, giant TER ratio and high performance can be achieved in FTJs constructed with 2D FEMs and metal contacts.