Metal–monolayer MoSi2N4 junctions: metal dimension dependent Fermi-level pinning

Abstract

High-performance semiconductor devices demand ohmic contacts with low contact resistances, while such low-resistance ohmic contacts are closely linked to the weak Fermi level pinning (FLP) effect. Conventionally, heterojunctions composed of two-dimensional (2D) metal electrodes and 2D semiconductors (e.g., MoS₂) exhibit weak FLP effects due to van der Waals (vdW) interfaces. In contrast, heterojunctions with three-dimensional (3D) metals have stronger interfacial interactions, which result in more intense pinning effects and Schottky barriers that are difficult to modulate. However, this conventional viewpoint is overturned in heterojunctions composed of metals and 2D semiconductors—MoSi₂N₄. In this study, we used first-principles calculations to investigate the interfacial properties of the monolayer MoSi₂N₄ with 3D metals and 2D metals as electrodes. Our results demonstrate that the FLP effect is more pronounced in 2D metal–MoSi₂N₄ heterojunctions rather than in 3D metal–MoSi₂N₄ heterojunctions—supported by FLP factor values: the factor S is approximately 0.4 for 2D metal–MoSi₂N₄versus 0.9 for 3D metal–MoSi₂N₄. We further analyzed the reasons: for 2D metals with extremely small work functions (below MoSi₂N₄'s electron affinity) or extremely large work functions (above MoSi₂N₄'s ionization energy), interfacial charge transfer induces a large interfacial dipole, triggering strong FLP. For 3D metal heterojunctions, MoSi₂N₄'s inherent shielding effect prevents strong chemical bonding at the interface and the large vdW interfacial distance causes significant decay of metal wave functions—thus weakening FLP. This study investigates the interfacial properties and FLP effect of metal–MoSi₂N₄, and the insights gained provide theoretical guidance for developing high-efficiency 2D semiconductor devices.