Molecular-Beam Epitaxy of Two-Dimensional In₂Se₃ and Its Giant Electroresistance Switching in Ferroresistive Memory Junction

Abstract

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 (InSe), 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-InSe on graphene and demonstrate the use of α-InSe 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 with a readout current density of >12 A/cm, which is more than 200% higher than the state-of-the-art technology. Our MBE growth method allows a high-quality ultrathin film of InSe to be heteroepitaxially grown on graphene, thereby simplifying the fabrication of high-performance 2D ferroelectric junctions for ferroresistive memory applications.

In-Plane Ferroelectric Tunnel Junction

“…Although SnTe nanoplates grown by molecular beam epitaxy (MBE) is not scalable at the moment, we believe that as more 2D ferroelectrics are being discovered, 2D ferroelectrics that can grow with uniform crystalline orientations can be found soon. For example, it is already found that In 2 Se 3 has in-plane polarization and can be grown by both MBE and CVD (chemical vapor deposition) [27][28][29][30]. We hope our design can open up a new direction of ferroelectric non-volatile memories.…”

“…Although it is predicted that in-plane polarization survives in the 2D limit [19], currently it is hard to prepare free-standing 2D perovskite ferroelectrics. Surprisingly, the recent discovered in-plane polarization in 2D ferroelectrics is enhanced instead of reduced in thin films [25,[27][28][29][30]. For example in SnTe, compared with the bulk ferroelectric transition temperature of 98K, the one monolayer (ML) thin film has a critical temperature of 270K, and thicker films with 3 ML show robust spontaneous polarization even at room temperature [25,26].…”

“…By choosing proper layer sizes and the insulator layer band gap, the tunneling current and the ON/OFF current ratio can be tuned simultaneously. In principle, all ferroelectric thin films with in-plane polarization can be used as the material platform to realize our proposal [20][21][22][23][24][25][26][27][28][29][30]. In particular, the recently discovered room-temperature IV-VI semiconductor thin films with robust in-plane polarization is an ideal candidate [25,26].…”

Degradable and Dissolvable Thin-Film Materials for the Applications of New-Generation Environmental-Friendly Electronic Devices

“…For 2D thin-film, a typical preparation method is a mechanical exfoliation, which was first used to prepare single-layer graphene in 2004 [18]. Since then, CVD [55], PLD [56], MBE [57], and pick-and-lift vdW techniques [58] were also used for preparing high-quality 2D thin films. Mechanical exfoliation is the main methodology to prepare the single-layer graphene.…”

Van der Waals Contact to 2D Semiconductors with a Switchable Electric Dipole: Achieving Both n‐ and p‐Type Ohmic Contacts to Metals with a Wide Range of Work Functions

“…Their potential applications in different fields have been demonstrated. The first class of 2D pS is group III 2 ‐VI 3 ferroelectrics (M 2 X 3 , M = Al, Ga, In; X = S, Se, Te),7,8 and some of them have been synthesized in experiment 4,9–13. Particularly, ferroelectric In 2 Se 3 had been applied to data storage with the switchable polarization, spintronics,9 and visible light absorption 10,14–17.…”