Interfacial chemistry at solid–liquid van der Waals heterojunctions enabling sub-5 nm Ohmic contacts for monolayer semiconductors

The decoupling of electronic states between metals and semiconductors through controlled construction of artificial van der Waals (vdW) heterojunctions enables tailored Schottky barriers. However, the interfacial chemistry, especially involving solid-liquid interfaces, remains unexplored. Here, first principles calculations reveal unexpected strong Fermi-level pinning in various metal/MoS₂ vdW heterojunctions with intercalated ice-like water bilayers. The polarization orientation of water in contact with metals of different work functions varies significantly, while the effective work function of the metals consistently decreases. Aluminum and scandium exhibit significant interfacial dipoles associated with hydrogen-bonding interactions when contacting MoS₂ with intercalated water, leading to heavily doped n-type Ohmic contacts. The contact length of a monolayer MoS₂ transistor with aluminum/intercalated-water (or hydroxyl) contacts can be scaled down to sub-5 nm due to a significant reduction in contact resistance, facilitated by strong interfacial charge transfer and hydrogen-bonding-enhanced resonant tunneling effects. This demonstrates a promising approach to regulating the contact properties via interfacial chemistry.