Ionic-Liquid Gated Bilayer MoS$_{2}$ Field-Effect Transistors

We report the electrical characterization of ionic-liquid-gated bilayer MoS$_{2}$ field-effect transistors. An On-Off current ratio greater than 10$^{6}$ is achieved for hole transport, while that for electron transport exceeds 10$^{8}$. The subthreshold swing of our bilayer MoS$_{2}$ devices reaches as low as 47 mV/dec at 230 K, approaching the theoretical limit. We also demonstrate that 1) the extrinsic mobility of back-gated MoS$_{2}$ field-effect transistors is largely limited by the contact resistance; and 2) the extremely large electrical-double-layer capacitance of ionic liquid significantly reduces the Schottky contact barrier leading up to three orders of magnitude mobility increase for electron transport.