Tunneling-Barrier-Free Ohmic Contacts at 2D Electride/Semiconductor Interfaces.

Abstract

Two-dimensional (2D) electrides, featuring an intrinsic nearly free surface electron gas and an ultralow work function, provide an effective platform for efficient charge injection. Their unconventional electronic structure makes them attractive electrode materials for 2D semiconductors. However, in van der Waals (vdW) metal-semiconductor junctions (MSJs), weak interlayer coupling introduces a tunneling barrier that severely limits carrier injection, despite suppressed interfacial disorder and Fermi-level pinning (FLP). Resolving this long-standing incompatibility between weak FLP and efficient carrier tunneling remains a key challenge in contact engineering for 2D electronics. Using first-principles calculations, we demonstrate that the MSJs formed between the 2D electride Ca₂N and MX₂ (M = Hf, Zr; X = S, Se) simultaneously achieve tunneling-barrier-free transport and intrinsic Ohmic contact behavior. Ca₂N forms strongly coupled donor-acceptor interfaces with MX₂, enabling barrier-free carrier injection while maintaining weak FLP. The MSJs exhibit intrinsic Ohmic contact behavior with a tunneling probability of 100%. Transport simulations further confirm the contact performance, with a ZrS₂/Ca₂N-based device delivering a current nearly 10⁴ μA/μm at a low bias of 0.2 eV. Moreover, bromination of the noncontact Ca₂N surface enhances high environmental stability without degrading interfacial electronic properties. These results establish 2D electrides as promising electrode materials for transition-metal dichalcogenide (TMD)-based nanoelectronics.