A Room Temperature Polariton Light-Emitting Diode Based on Monolayer WS2

Abstract: 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.