Unlocking the ideal ohmic contacts in MoSi₂N₄via MSene electrodes

The pursuit of low-resistance ohmic contacts in two-dimensional semiconductor devices remains a critical challenge for practical applications. Here, using first-principles calculations, we investigate the interfacial contact properties between monolayer MoSi₂N₄ and three MSene electrodes (M₂S, M = V, Mo, W). After identifying the most stable stacking configuration, we find a systematic Schottky-to-Ohmic transition from V₂S to W₂S, driven by increasing interfacial charge transfer from the semiconductor to the metal. Notably, W₂S/MoSi₂N₄ forms an ideal n-type ohmic contact with zero Schottky barrier. Moreover, all three heterostructures exhibit vanishing tunneling barriers, attributable to covalent-like quasi-bonding interactions at the short interlayer spacings. Although conventional barrier engineering via interlayer compression is precluded by the already near-covalent distances, external electric fields can still modulate the Schottky barrier, albeit with reduced efficiency. Our results establish W₂S as a promising electrode candidate for MoSi₂N₄-based devices and provide insights into dipole engineering for contact optimization in strongly coupled van der Waals heterostructures.