Understanding contact to ballistic and quasi-ballistic transition-metal dichalcogenide semiconductors

A contact model for ballistic and quasi-ballistic transport in two-dimensional (2D) semiconductors is presented. Improving transport properties in 2D semiconductors is essential for reducing contact resistance, but it drives carrier transport in the contact region into the quasi-ballistic regime, where the commonly used diffusive contact model breaks down. The proposed model captures the quantum limit of contact resistance in the ballistic limit when the metal–semiconductor interfacial resistivity is negligible and provides a framework for understanding the combined effects of carrier scattering and finite interfacial resistivity, which lead to the larger resistance values observed experimentally. The interplay between interfacial contact resistivity and quasi-ballistic transport in 2D semiconductors plays an important role in determining contact resistance and contact transfer length. The effects of contact length scaling and band non-parabolicity on the contact resistance are also examined. Numerical results are presented for monolayer transition-metal dichalcogenide semiconductors, using monolayer MoS2 as a representative example.