Controllable Polarization and Doping in Ferroelectric In₂Se₃ Monolayers and Heterobilayers via Intrinsic Defect Engineering

Two-dimensional (2D) ferroelectric In₂Se₃ with rarely discovered out-of-plane polarization has great potentials in advanced electronic and electromechanical applications. Considering that point defects are ineluctable in practical applications and may greatly influence the electronic properties, we systematically investigate the stability, induced conductive type, and electric polarization of defects in 2D In₂Se₃ (D-In₂Se₃) monolayers and In₂Se₃-graphene heterobilayers through first principles calculations. Among the 40 kinds of considered vacancies, the decentralized vacancy possesses relatively high stability. In addition, the difficulty in migration of these vacancies leads to the localized electronic effect. The n- and p-doped conditions are, respectively, achieved by single In and surface Se vacancies in the D-In₂Se₃ monolayers. Their out-of-plane polarity can also be regulated by the types and concentrations of vacancies due to the induced charge redistribution. More interestingly, different from the perfect In₂Se₃–graphene heterobilayer, where only n-type graphene can be achieved, the existence of surface Se vacancies in the D-In₂Se₃ layer can toggle the conductive type of the graphene layer between p- and n-doped conditions by reversing its electric polarization, suggesting the applications in the electric-controlled p–n junction. This work establishes the theoretical foundation for the influence of intrinsic vacancies on electronic and ferroelectric properties in the D-In₂Se₃ monolayer and heterobilayer, providing the application guides on 2D ferroelectrics by defect engineering.