Barrier-Free Carrier Injection in 2D WSe₂/MoSe₂ Heterostructures via Fermi-Level Depinning

Transition metal dichalcogenide (TMDC)-based two-dimensional (2D) type-II van der Waals heterostructures exhibit remarkable potential in next-generation optoelectronics, valleytronics, and spintronics. Nevertheless, the inevitable Fermi level pinning (FLP) effect at metal/TMDC interfaces intrinsically leads to elevated Schottky barrier heights (SBHs) and consequent contact resistance degradation. In this work, we present a first-principles investigation on the interfacial physics of metal-contacted WSe₂/MoSe₂ heterostructures with four representative electrodes (Ag, Al, Au, Pt). All the metal-WSe2/MoSe2 contacts induce significant metal-induced gap states (MIGSs), which are responsible for FLP inside the WSe2/MoSe2 band gaps. Ag-MoSe2 contact has the minimum electron SBH of 0.31 eV, where the Pt-WSe2 exhibits a minimum hole SBH of 0.43 eV. Upon inserting a 2D metal-doped metallic mWSe/mMoSe layer between WSe2/MoSe2 layer and metal electrodes, the MIGSs arising from the penetration of metal wave functions into the semiconductor layers can be effectively suppressed, leading to practically negligible SBHs both for electron and hole, and even a vanishing SBH is obtained, suggesting a high carrier injection efficiency. The achieved quasi-Ohmic contact characteristics provide a universal design paradigm for high-performance TMDC-based devices requiring ultralow contact resistance.