Polarity-selective Ohmic contact enabled by intercalation-engineering on a 2D graphene electrode

Tailoring polarity-matched Ohmic contact (OhC) is critical for efficient carrier injection in two-dimensional (2D) semiconductor devices. Typically, doping-induced metallization, surface functionalization, and modulation doping of the channel inevitably degrade the intrinsic properties of 2D semiconductors and suffer from limited stability and poor controllability. To address these challenges, we introduce a facile and efficient intercalation-engineering strategy using bilayer graphene electrodes to achieve polarity-selective OhC. Zero-dimensional intercalation of transition-metal cations, serving as electron sources, effectively lowers the system's electron affinity. Among a series of cations, Y intercalation reduces the bilayer graphene work function to a minimum of 3.55 eV, comparable to that of the strong electron donor 2D Ca₂N, thereby facilitating electron OhC with n-type 2D semiconductors. Remarkably, a NaCl₂ monolayer sandwiched within bilayer graphene, recently realized experimentally, represents a natural 2D intercalation paradigm. The resulting strong hole doping induced by NaCl₂ increases the graphene work function by 0.79 eV, promoting hole OhC with p-type 2D semiconductors. This work establishes a conceptually new approach for achieving polarity-matched OhC through controlled doping of 2D metallic electrodes, offering a broadly generalizable route for engineering high-performance contacts in diverse 2D material systems.