  Layered two-dimensional (2D) semiconducting transition metal dichalcogenides
(TMD) have been widely isolated, synthesized, and characterized recently.
Numerous 2D materials are identified as the potential candidates as channel
materials for future thin film technology due to their high mobility and the
exhibiting bandgaps. While many TMD filed-effect transistors (FETs) have been
widely demonstrated along with a significant progress to clearly understand the
device physics, large contact resistance at metal/semiconductor interface still
remain a challenge. From 2D device research point of view, how to minimize the
Schottky barrier effects on contacts thus reduce the contact resistance of
metals on 2D materials is very critical for the further development of the
field. Here, we present a review of contact research on molybdenum disulfide
and other TMD FETs from the fundamental understanding of metal-semiconductor
interfaces on 2D materials. A clear contact research strategy on 2D
semiconducting materials is developed for future high-performance 2D FETs with
aggressively scaled dimensions.
