INSP – Sorbonne Université – 4 place Jussieu – 75005 Paris – Barre 12-22, 4e étage, salle 426
Emmanuel Baudin, LPENS
Abstract
In this seminar, I will present our recent discovery of graphene’s electroluminescence in the middle infrared.
Electroluminescence is the phenomenon by which a material emits light in response to the passage of an electrical current. In solids, it is the prerogative of semiconductors and related organic materials, and it results from the radiative recombination of electrons and holes.
We study high mobility graphene field effect transistors at room temperature and ambient conditions. These transistors are made of a monolayer graphene flake encapsulated in a hexagonal Boron nitride insulator. When submitted to a large bias, we observe the appearance of a sharp emission peak at a photon energy of 190meV in the far field radiation of the transistor. Using a series of test experiments, we show the electroluminescent nature of this emission.
The semi-metallic nature of graphene a priori forbids electroluminescence: Indeed, in semiconductors, the bandgap energetically insulates the electrons from the holes. Such protection doesn’t exist in graphene which is gapless. Nonetheless, electroluminescence is possible, because (i) of the remarkable inefficiency of the non-radiative carrier relaxation in graphene, and (ii) thanks to an original carrier injection mechanism specific to 2D semimetals: the Zener-Klein (ZK) tunnel conductance.
Using electronic noise thermometry experiments, we observe that the electroluminescence of graphene is signaled by a strong cooling of the electron gas at large bias; an effect well known in regular electroluminescent devices near the electroluminescent threshold. Finally, I will discuss the microscopic mechanisms at stake, and in particular, the crucial role of the encapsulate in the emitted light spectrum.
