  Two-dimensional (2D) layered materials-based field-effect transistors (FETs)
are promising for ultimate scaled electron device applications because of the
improved electrostatics to atomically thin body thickness. However, compared
with the typical thickness of ~5-nm for Si-on-insulator (SOI), the advantage of
the ultimate thickness limit of monolayer for the device performance has not
been fully proved yet, especially for the on-state at the accumulation region.
Here, we present much stronger quantum-mechanical effect at the accumulation
region based on the C-V analysis for top-gate MoS2 FETs. The self-consistent
calculation elucidated that the electrons are confined in the monolayer
thickness, unlike in the triangle potential formed by the electric field for
SOI, the gate-channel capacitance is ideally maximized to the gate insulator
capacitance since the capacitive contribution of the channel can be neglected
due to the negligible channel thickness. This quantum-mechanical effect agreed
well with the experimental results. Therefore, monolayer 2D channels are
suggested to be used to enhance the on-current as well as the gate modulation
ability.
