Integration of graphene and two-dimensional ferroelectrics: properties and related functional devices

Ferroelectric (FE) thin films have been investigated for many years due to their broad applications in electronic devices. It was recently demonstrated that FE functionality persists in ultrathin films, possibly even in monolayers of two-dimensional (2D) FEs. However, the feasibility of 2D-based FE functional devices remains an open challenge. Here, we employ density-functional-theory calculations to propose and document the possible integration of graphene with 2D FE materials on metal substrates in the form of functional FE devices. We show that monolayers of proposed M₂O₃ (M = Al, Y) in the quintuple layer (QL) In₂Se₃ structure are stable 2D FE materials and that QL-M₂O₃ is a functional tunnel barrier in a graphene/QL-M₂O₃/Ru heterostructure. The QL-M₂O₃ barrier width can be modulated by its polarization direction, whereby the heterostructure can function as a prototype ferroelectric tunnel junction. Moreover, alternating the polarization of QL-M₂O₃ modulates the doping type of graphene, enabling the fabrication of graphene p-n junctions. By design, the proposed heterostructures can in principle be fabricated by intercalation, which is known to produce high-quality, large-scale 2D-based heterostructures.