Ambipolar Light-Emitting Transistors on Chemical Vapor\nDeposited Monolayer MoS₂

Abstract

We realize and investigate ionic\nliquid gated field-effect transistors (FETs) on large-area MoS₂ monolayers grown by chemical vapor deposition (CVD). Under\nelectron accumulation, the performance of these devices is comparable\nto that of FETs based on exfoliated flakes. FETs on CVD-grown material,\nhowever, exhibit clear ambipolar transport, which for MoS₂ monolayers had not been reported previously. We exploit this property\nto estimate the bandgap Δ of monolayer MoS₂ directly\nfrom the device transfer curves and find Δ ≈ 2.4–2.7\neV. In the ambipolar injection regime, we observe electroluminescence\ndue to exciton recombination in MoS₂, originating from\nthe region close to the hole-injecting contact. Both the observed\ntransport properties and the behavior of the electroluminescence can\nbe consistently understood as due to the presence of defect states\nat an energy of 250–300 meV above the top of the valence band,\nacting as deep traps for holes. Our results are of technological relevance,\nas they show that devices with useful optoelectronic functionality\ncan be realized on large-area MoS₂ monolayers produced\nby controllable and scalable techniques.