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CeNS Colloquium

Kleiner Physikhörsaal, LMU
Date: 23.6.2017, Time: 15:30h

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 [1], and also the operation of field emitter display-type devices in the deep ultraviolet [2]. 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 [3].

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 [4]. 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 [5]. 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 [6]. I will finally present optical characterization results of the promising high-temperature MBE growth of hBN, in collaboration with Nottingham University [7].



[1] K. Watanabe, T. Taniguchi, and H. Kanda, Nature Mater. 3, 404 (2004).

[2] K. Watanabe, T. Taniguchi, T. Niiyama, K. Miya, and M. Taniguchi, Nature Photon. 3, 591 (2009).

[3] A. K. Geim and I. V. Grigorieva, Nature 499, 419 (2013).

[4] G. Cassabois, P. Valvin, B. Gil, Nat. Photonics 10, 262 (2016).

[5] P. Vuong, G. Cassabois, P. Valvin, V. Jacques, A. Van Der Lee, A. Zobelli, K. Watanabe, T. Taniguchi, and B. Gil, 2D Mater. 4, 011004 (2017).

[6] P. Vuong, G. Cassabois, P. Valvin, V. Jacques, R. Cuscó, L. Artús, and B. Gil, Phys. Rev. B 95, 045207 (2017).

[7] P. Vuong, G. Cassabois, P. Valvin, E. Rousseau, A. Summerfield, C. J. Mellor, Y. Cho, T. S. Cheng, J. D. Albar, L. Eaves, C. T. Foxon, P. H. Beton, S. V. Novikov, and B. Gil, 2D Mater. 4, 021023 (2017).