Monolayer tungsten diselenide (1L-WSe2) has recently received attention because of its favourable band structure for probing novel correlated phenomena of p-type carriers, such as interaction-driven and topological insulating phases and superconductivity in twisted bilayers, and Bose-Einstein condensation of excitons in double-layer heterostructures. However, electrical transport studies have been impeded by the lack of a reliable method to realize Ohmic hole-conducting contacts to 1L-WSe2 especially at low carrier densities and low temperatures. Here, we present low-temperature p-type Ohmic contact to 1L-WSe2 field-effect transistors at carrier densities (n) below n = 1 × 1012 cm−2. Monolayer WSe2 was sandwiched by hexagonal boron nitride flakes by a dry transfer technique and electrically contacted with 20 nm thick amorphous MoO3 followed by Pd metal. The finding of p-type Ohmic contact is supported by linear current-voltage characteristics down to a temperature of 10 K and carrier densities from n = 7.7 × 1011 cm−2 to below the threshold, temperature-independent output curves up to room temperature, and negligible contact barrier down to subthreshold regime. Furthermore, the contact resistivity of MoO3-contacted 1L-WSe2 FET is 30.2–64.8 kΩ·μm at n = 1.5 × 1012 cm−2, which is the lowest reported for 1L-WSe2 FETs at such low carrier density. Achieving p-type Ohmic contact in 1L-WSe2 FETs will enable direct electronic measurements of quantum transport in correlated phases in the valence bands of monolayer semiconductors.
About the presenter
Yi-Hsen Chen is a PhD student at Monash University with CI Michael Fuhrer. He researches Bose-Einstein condensates using devices constructed using 2D materials, as part of FLEET’s Research Theme 2, Exciton Superfluids.