  Two-dimensional (2D) materials are a new class of materials with interesting
physical properties and ranging from nanoelectronics to sensing and photonics.
In addition to graphene, the most studied 2D material, monolayers of other
layered materials such as semiconducting dichalcogenides MoS2 or WSe2 are
gaining in importance as promising insulators and channel materials for
field-effect transistors (FETs). The presence of a direct band gap in monolayer
MoS2 due to quantum mechanical confinement, allows room-temperature
field-effect transistors with an on/off ratio exceeding 108. The presence of
high-k dielectrics in these devices enhanced their mobility, but the mechanisms
are not well understood. Here, we report on electrical transport measurements
on MoS2 FETs in different dielectric configurations. Mobility dependence on
temperature shows clear evidence of the strong suppression of charge impurity
scattering in dual-gate devices with a top-gate dielectric together with phonon
scattering that shows a weaker than expected temperature dependence. High
levels of doping achieved in dual-gate devices also allow the observation of a
metal-insulator transition in monolayer MoS2. Our work opens up the way to
further improvements in 2D semiconductor performance and introduces MoS2 as an
interesting system for studying correlation effects in mesoscopic systems.
