sp² to sp³ hybridization transformation in 2D metal-semiconductor contact interface suppresses tunneling barrier and Fermi level pinning simultaneously

Van der Waals (vdWs) stacking of two-dimensional (2D) materials can effectively weaken the Fermi level pinning (FLP) effect in metal/semiconductor contacts due to dangling-bond-free surfaces. However, the inherent vdWs gap always induces a considerable tunneling barrier, significantly limiting carrier injection. Herein, by inducing a sp² to sp³ hybridization transformation in 2D carbon-based metal via surface defect engineering, the large orbital overlap can form an efficient carrier channel, overcoming the tunneling barrier. Specifically, by selecting the 2D carbon-based X₃C₂ (X = Cd, Hg, and Zn) metal and the 2D MSi₂N₄ (M = Cr, Hf, Mo, Ti, V, and Zr) semiconductor, we constructed 36 metal/semiconductor contacts. For vdWs contacts, although Ohmic contacts can be formed at the interface, the highest tunneling probability (P_TB) is only 3.11%. As expected, the P_TB can be significantly improved, as high as 48.73%, when MSi₂N₄, accompanied by surface nitrogen vacancies, forms an interface covalent bond with X₃C₂. Simultaneously, weak FLP and Ohmic contact remain at the covalent-bond-based surface, attributing to the protection of the MSi₂N₄ band-edge electronic states by the outlying Si-N sublayer. Our work provides a promising path for advancing the progress of 2D electronic and photoelectronic devices.