Theoretical predication of two-dimensional ferroelectric metal X2Y3 monolayer and Van der Waals heterostructures

Two-dimensional (2D) ferroelectric metal materials are attaching intense attention due to its spontaneous ferroelectric polarization and metallic characteristics. However, few 2D ferroelectric metals have been reported, which hinders its possible applications for electronic devices. Here, we systematically predicted the monolayer IV-V X2Y3 (X = C, Si, Ge, Sn; Y=N, P, As, Sb) material by first-principles calculation, finding that eight kinds of ferroelectric metals (Si2P3, Si2As3, Si2Sb3, Ge2P3, Ge2As3, Sn2P3, Sn2As3 and Sn2Sb3) are thermodynamically stable with different out-of-plane polarization. Moreover, for the monolayer X2Y3/graphene heterostructures, the ferroelectric polarization can induce p-type doping of graphene. When the ferroelectric metal contacts with 2D semiconductor, the Schottky barrier height can be formed and effectively changed by polarization reversal. This work has greatly enriched the 2D ferroelectric metal family, and explored possible applications of 2D ferroelectric metal materials.