Jeudi 9 mars à 10h00,
Salle Remy Lemaire, K223
Orateur : Guillaume Cassabois (Laboratoire C. Coulomb, Montpellier)
" Hexagonal boron nitride : a wide bandgap semiconductor with unique opto-electronic properties"
Hexagonal boron nitride (hBN) is a wide bandgap semiconductor with a large range of basic applications relying on its low dielectric constant, high thermal conductivity, and chemical inertness. The growth of high-quality crystals in 2004 has revealed that hBN is also a promising material for light-emitting devices in the deep ultraviolet domain, as illustrated by the demonstration of lasing at 215 nm by accelerated electron excitation, and also the operation of field emitter display-type devices in the deep ultraviolet. With a honeycomb structure similar to graphene, bulk hBN has recently gained tremendous attention as an exceptional substrate for graphene with an atomically smooth surface, and more generally, as a fundamental building block of Van der Waals heterostructures. I will review the recent advances elucidating the opto-electronic properties of this lamellar compound. I will discuss the impact on the optical response of the unusual configuration of the bandstructure, where both the conduction and valence bands have extrema at edges of the Brillouin zone. I will present experimental results demonstrating that the emission spectrum consists of phonon replicas involving phonons of different symmetries and of different group velocities. Finally, I will present measurements of high-quality hBN grown by molecular beam epitaxy.