High mobility WSe₂ p - And n - Field-effect transistors contacted by highly doped graphene for low-resistance contacts

We report the fabrication of both n-type and p-type WSe₂ field-effect transistors with hexagonal boron nitride passivated channels and ionic-liquid (IL)-gated graphene contacts. Our transport measurements reveal intrinsic channel properties including a metal-insulator transition at a characteristic conductivity close to the quantum conductance e²/h, a high ON/OFF ratio of >10⁷ at 170 K, and large electron and hole mobility of μ ≈ 200 cm² V^-1s^-1 at 160 K. Decreasing the temperature to 77 K increases mobility of electrons to ∼330 cm² V^-1 s^-1 and that of holes to ∼270 cm² V^-1 s^-1. We attribute our ability to observe the intrinsic, phonon-limited conduction in both the electron and hole channels to the drastic reduction of the Schottky barriers between the channel and the graphene contact electrodes using IL gating. We elucidate this process by studying a Schottky diode consisting of a single graphene/WSe₂ Schottky junction. Our results indicate the possibility to utilize chemically or electrostatically highly doped graphene for versatile, flexible, and transparent low-resistance ohmic contacts to a wide range of quasi-2D semiconductors.