Reversible doping polarity and ultrahigh carrier density in two-dimensional van der Waals ferroelectric heterostructures

Van der Waals semiconductor heterostructures (VSHs) composed of two or more two-dimensional (2D) materials with different band gaps exhibit huge potential for exploiting high-performance multifunctional devices. The application of 2D VSHs in atomically thin devices highly depends on the control of their carrier type and density. Herein, on the basis of comprehensive first-principles calculations, we report a new strategy to manipulate the doping polarity and carrier density in a class of 2D VSHs consisting of atomically thin transition metal dichalcogenides (TMDs) and α-In2X3 (X = S, Se) ferroelectrics via switchable polarization field. Our calculated results indicate that the band bending of In2X3 layer driven by the FE polarization can be utilized for engineering the band alignment and doping polarity of TMD/In2X3 VSHs, which enables us to control their carrier density and type of the VSHs by the orientation and magnitude of local FE polarization field. Inspired by these findings, we demonstrate that doping-free p—n junctions achieved in MoTe2/In2Se3 VSHs exhibit high carrier density ( $${10^{{1_3}}} - {10^{{1_4}}}\,{\rm{c}}{{\rm{m}}^{ - 2}}$$ ), and the inversion of the VHSs from n—p junctions to p—i—n junctions has been realized by the polarization switching from upward to downward states. This work provides a nonvolatile and nondestructive doping strategy for obtaining programmable p—n van der Waals (vdW) junctions and opens the possibilities for self-powered and multifunctional device applications.