Contact Resistance in Monolayer MoS2 Edge-Contacts: “Electrostatic” vs. Substitutional Doping

We present results on the effect of a surrounding dielectric and a back-gate bias on the resistance of “electrostatically” doped two-dimensional (2D) materials edge-contacts and compare it to contacts to impurity-doped 2D materials. The transmission probability is computed using the Wentzel-Kramers-Bril-louin approximation, the full-band density of states obtained from density functional theory, and the potential is obtained from the 2D Poisson's equation. We find that a low-x back-gate oxide with a low-k top dielectric environment results in a lower contact re-sistance in “electrostatically” doped edge-contacts. The image-force barrier-lowering is reduced by the back-gate, whereas in im-purity doped contacts, it is determined by the dielectric permittiv-ity of the surrounding oxide and of the 2D material. Additionally, we observed that in all cases, “electrostatically” doped devices ex-hibit worse contact resistance than impurity doped ones, and only very high gate bias, such as $> 1\mathrm{V}$, can yield sufficiently low contact resistance when using a high- $k$ back gate oxide.