Visualizing interface states in In ₂Se ₃-WSe ₂ monolayer lateral heterostructures

Recent findings of two-dimensional (2D) ferroelectric (FE) materials provide more possibilities for the development of 2D FE heterostructure electronic devices based on van der Waals materials and the application of FE devices under the limit of atomic layer thickness. In this paper, we report the in-situ fabrication and probing of electronic structures of In ₂Se ₃–WSe ₂ lateral heterostructures, compared with most vertical FE heterostructures at present. Through molecular beam epitaxy, we fabricated lateral heterostructures with monolayer WSe ₂ (three atomic layers) and monolayer In ₂Se ₃ (five atomic layers). Type-II band alignment was found to exist in either the lateral heterostructure composed of anti-FE β′-In ₂Se ₃ and WSe ₂ or the lateral heterostructure composed of FE β*-In ₂Se ₃ and WSe ₂, and the band offsets could be modulated by ferroelectric polarization. More interestingly, interface states in both lateral heterostructures acted as narrow gap quantum wires, and the band gap of the interface state in the β*-In ₂Se ₃–WSe ₂ heterostructure was smaller than that in the β′-In ₂Se ₃ heterostructure. The fabrication of 2D FE heterostructure and the modulation of interface state provide a new platform for the development of FE devices.