Molecular-Beam Epitaxy of Two-Dimensional In<sub>2</sub>Se<sub>3</sub> and Its Giant Electroresistance Switching in Ferroresistive Memory Junction

Ferroelectric thin film has attracted great interest for nonvolatile memory applications and can be used in either ferroelectric Schottky diodes or ferroelectric tunneling junctions due to its promise of fast switching speed, high on-to-off ratio, and nondestructive readout. Two-dimensional α-phase indium selenide (In<sub>2</sub>Se<sub>3</sub>), which has a modest band gap and robust ferroelectric properties stabilized by dipole locking, is an excellent candidate for multidirectional piezoelectric and switchable photodiode applications. However, the large-scale synthesis of this material is still elusive, and its performance as a ferroresistive memory junction is rarely reported. Here, we report the low-temperature molecular-beam epitaxy (MBE) of large-area monolayer α-In<sub>2</sub>Se<sub>3</sub> on graphene and demonstrate the use of α-In<sub>2</sub>Se<sub>3</sub> on graphene in ferroelectric Schottky diode junctions by employing high-work-function gold as the top electrode. The polarization-modulated Schottky barrier formed at the interface exhibits a giant electroresistance ratio of 3.9 × 10<sup>6</sup> with a readout current density of >12 A/cm<sup>2</sup>, which is more than 200% higher than the state-of-the-art technology. Our MBE growth method allows a high-quality ultrathin film of In<sub>2</sub>Se<sub>3</sub> to be heteroepitaxially grown on graphene, thereby simplifying the fabrication of high-performance 2D ferroelectric junctions for ferroresistive memory applications.