Hexagonal boron nitride: a semiconductor with unique opto-electronic properties
Guillaume Cassabois, Laboratoire Charles Coulomb (L2C), Univ. Montpellier, CNRS, Montpellier, France
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 discuss our recent studies showing that the optical response in hBN displays prominent evidence for phonon-assisted optical transitions, with a very unusual phenomenology. By two-photon spectroscopy, we demonstrated that the intrinsic optical properties at the band edge are characteristic of an indirect bandgap material . Polarization-resolved experiments with a detection from the sample edge allowed us to show that the phonon symmetries can be traced back in the optical response . I will further highlight the unique properties of this material where the optical response is tailored by the phonon group velocities in the middle of the Brillouin zone . I will finally present optical characterization results of the promising high-temperature MBE growth of hBN, in collaboration with Nottingham University .
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