Filtering the photoluminescence spectra of atomically thin semiconductors with graphene

Etienne Lorchat, Luis E. Parra López, Cédric Robert, Delphine Lagarde, Guillaume Froehlicher, Takashi Taniguchi, Kenji Watanabe, Xavier Marie, Stéphane Berciaud

Published 2019-08-28Version 1

Atomically thin semiconductors made from transition metal dichalcogenides (TMDs) are model systems for investigations of strong light-matter interactions and applications in nanophotonics, opto-electronics and valley-tronics. However, the typical photoluminescence spectra of TMD monolayers display a large number of intrinsic and extrinsic features that are particularly challenging to decipher. On a practical level, monochromatic TMD-based emitters would be beneficial for low-dimensional devices but no solution has yet been found to meet this challenge. Here, using a counter-intuitive strategy that consists in interfacing TMD monolayers with graphene, a system known as an efficient luminescence quencher, we demonstrate bright, single and narrow-line photoluminescence arising solely from TMD neutral excitons. This observation stems from two effects: (i) complete neutralization of the TMD by the adjacent graphene leading to the absence of optical features from charged excitons (ii) selective non-radiative transfer of TMD excitons to graphene, that is sufficiently rapid to quench radiative recombination of long-lived excitonic species without significantly affecting bright excitons, which display much shorter, picosecond radiative lifetimes at low temperatures. Our approach is systematically applied to four tungsten and molybdenum-based TMDs and establishes TMD/graphene heterostructures as a unique set of opto-electronic building blocks. Graphene not only endows TMDs monolayers with superior optical performance and enhanced photostability but also provides an excellent electrical contact, suitable for TMD-based electroluminescent systems emitting visible and near-infrared photons at near THz rate with linewidths approaching the lifetime limit.