Achieving high carrier density and high mobility in graphene using monolayer tungsten oxyselenide

Highly doped graphene holds promise for next-generation electronic and photonic devices. However, chemical doping cannot be precisely controlled, and introduces external disorder that significantly diminishes the carrier mobility and therefore the graphene conductivity. Here, we show that monolayer tungsten oxyselenide (TOS) created by oxidation of WSe2 acts as an efficient and low-disorder hole-dopant for graphene. When the TOS is directly in contact with graphene, the induced hole density is 3 × 1013 cm-2 , and the room-temperature mobility is 2,000 cm2 /V·s, far exceeding that of chemically-doped graphene. Inserting WSe2 layers between the TOS and graphene tunes the induced hole density as well as reduces charge disorder such that the mobility exceeds 20,000 cm2 /V·s and reaches the limit set by acoustic phonon scattering, resulting in sheet resistance below 50 Ω/□. An electrostatic model based on work-function mismatch accurately describes the tuning of the carrier density with WSe2 interlayer thickness. These films show unparalleled performance as transparent conductors at telecommunication wavelengths, as shown by measurements of transmittance in thin films and insertion loss in photonic ring resonators. This work opens up new avenues in optoelectronics incorporating two-dimensional heterostructures including infrared transparent conductors, electro-phase modulators, and various junction devices.