Ambipolar Light-Emitting Transistors on Chemical Vapor Deposited Monolayer MoS2

TL;DR

This paper demonstrates ambipolar light-emitting transistors on large-area CVD-grown monolayer MoS2, revealing new transport properties, estimating the bandgap, and observing electroluminescence, with implications for scalable optoelectronic devices.

Contribution

It reports the first observation of ambipolar transport and electroluminescence in CVD-grown MoS2 monolayer transistors, enabling scalable optoelectronic applications.

Findings

Ambipolar transport observed in CVD-grown MoS2 transistors.

Electroluminescence due to exciton recombination near hole-injecting contact.

Estimated bandgap of MoS2 monolayer as approximately 2.4-2.7 eV.

Abstract

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