Improving Electric Contacts to Two-Dimensional Semiconductors

TL;DR

This paper models and analyzes the factors affecting contact resistance in 2D semiconductor FETs, highlighting the limitations imposed by the vdW gap and proposing doping and patterning as mitigation strategies.

Contribution

It introduces a model separating current crowding effects from intrinsic resistivity and compares theoretical predictions with experimental data for doped and undoped MoS2.

Findings

Current crowding significantly increases contact resistance.

Doping and patterning can reduce contact resistance.

The vdW gap limits the minimum achievable contact resistance.

Abstract

Electrical contact resistance to two-dimensional (2D) semiconductors such as monolayer MoS_{2} is a key bottleneck in scaling the 2D field effect transistors (FETs). The 2D semiconductor in contact with three-dimensional metal creates unique current crowding that leads to increased contact resistance. We developed a model to separate the contribution of the current crowding from the intrinsic contact resistivity. We show that current crowding can be alleviated by doping and contact patterning. Using Landauer-B\"uttiker formalism, we show that van der Waals (vdW) gap at the interface will ultimately limit the electrical contact resistance. We compare our models with experimental data for doped and undoped MoS_{2} FETs. Even with heavy charge-transfer doping of > 2x10^{13} cm^{-2}, we show that the state-of-the-art contact resistance is 100 times larger than the ballistic limit. Our study highlights the need to develop efficient interface to achieve contact resistance of < 10 {\Omega}.{\mu}m, which will be ideal for extremely scaled devices.