Improved Carrier Mobility in Few-Layer MoS₂ Field-Effect Transistors with Ionic-Liquid Gating

We report the fabrication of ionic liquid (IL)-gated field-effect transistors (FETs) consisting of bilayer and few-layer MoS2. Our transport measurements indicate that the electron mobility μ ≈ 60 cm(2) V(-1) s(-1) at 250 K in IL-gated devices exceeds significantly that of comparable back-gated devices. IL-FETs display a mobility increase from ≈ 100 cm(2) V(-1) s(-1) at 180 K to ≈ 220 cm(2) V(-1) s(-1) at 77 K in good agreement with the true channel mobility determined from four-terminal measurements, ambipolar behavior with a high ON/OFF ratio >10(7) (10(4)) for electrons (holes), and a near ideal subthreshold swing of ≈ 50 mV/dec at 250 K. We attribute the observed performance enhancement, specifically the increased carrier mobility that is limited by phonons, to the reduction of the Schottky barrier at the source and drain electrode by band bending caused by the ultrathin IL dielectric layer.