  Achieving good electrical contacts is one of the major challenges in
realizing devices based on atomically thin two-dimensional (2D) semiconductors.
Several studies have examined this hurdle, but a universal understanding of the
contact resistance and an underlying approach to its reduction are currently
lacking. In this work we expose the shortcomings of the classical contact
resistance model in describing contacts to 2D materials, and offer a correction
based on the addition of a lateral pseudo-junction resistance component (Rjun).
We use a combination of unique contact resistance measurements to
experimentally characterize Rjun for Ni contacts to monolayer MoS2. We find
that Rjun is the dominating component of the contact resistance in undoped 2D
devices and show that it is responsible for most of the back-gate bias and
temperature dependence. Our corrected model and experimental results help
understand the underlying physics of state-of-the-art contact engineering
approaches in the context of minimizing Rjun.
