  Ultrathin two-dimensional semiconductors obtained from layered
transition-metal dichalcogenides such as molybdenum disulfide (MoS2) are
promising for ultimately scaled transistors beyond Si. Although the shortening
of the semiconductor channel is widely studied, the narrowing of the channel,
which should also be important for scaling down the transistor, has been
examined to a lesser degree thus far. In this study, the impact of narrowing on
mechanically exfoliated MoS2 flakes was investigated according to the
channel-width-dependent Schottky barrier heights at Cr/Au contacts. Narrower
channels were found to possess a higher Schottky barrier height, which is
ascribed to the edge-induced band bending in MoS2. The higher barrier heights
degrade the transistor performance as a higher electrode-contact resistance.
Theoretical analyses based on Poisson's equation showed that the edge-induced
effect can be alleviated by a high dopant impurity concentration, but this
strategy should be limited to channel widths of roughly 0.7 micrometers because
of the impurity-induced charge-carrier mobility degradation. Therefore, proper
termination of the dangling bonds at the edges should be necessary for
aggressive scaling with layered semiconductors.
