  Half-light half-matter quasiparticles termed exciton-polaritons arise through
the strong coupling of excitons and cavity photons. They have been used to
demonstrate a wide array of fundamental phenomena and potential applications
ranging from Bose-Einstein like condensation to analog Hamiltonian simulators
and chip-scale interferometers. Recently the two dimensional transition metal
dichalcogenides (TMDs) owing to their large exciton binding energies,
oscillator strength and valley degree of freedom have emerged as a very
attractive platform to realize exciton-polaritons at elevated temperatures.
Achieving electrical injection of polaritons is attractive both as a precursor
to realizing electrically driven polariton lasers as well as for high speed
light-emitting diodes (LED) for communication systems. Here we demonstrate an
electrically driven polariton LED operating at room temperature using monolayer
tungsten disulphide (WS2) as the emissive material. To realize this device, the
monolayer WS2 is sandwiched between thin hexagonal boron nitride (hBN) tunnel
barriers with graphene layers acting as the electrodes. The entire tunnel LED
structure is embedded inside a one-dimensional distributed Bragg reflector
(DBR) based microcavity structure. The extracted external quantum efficiency is
~0.1% and is comparable to recent demonstrations of bulk organic and carbon
nanotube based polariton electroluminescence (EL) devices. The possibility to
realize electrically driven polariton LEDs in atomically thin semiconductors at
room temperature presents a promising step towards achieving an inversionless
electrically driven laser in these systems as well as for ultrafast microcavity
LEDs using van der Waals materials.
