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One- and two-photon spectroscopy in hexagonal boron nitride
Auteur(s): Cassabois G.
Conférence invité: PLMCN17 (Nara, JP, 2016-03-28)
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Résumé: I will discuss our recent experiments by one- and two-photon spectroscopy demonstrating that hBN is an indirect bandgap material. I will show that the optical properties of hBN are profoundly determined by phonon-assisted transitions involving either virtual or real excitonic states. I will present our measurements of the exciton binding energy by two-photon excitation, leading to the estimation of 6.08 eV for the single-particle bandgap in hBN.
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Enhancing carbon-nanotubes luminescence with the help of resonant hotspots
Auteur(s): Rousseau E., Beaufils C., Cassabois G.
Conférence invité: Advances in Photonics and Applications (Florence, IT, 2016-06-09)
Texte intégral en Openaccess :
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Résumé: In this talk we will present experimental results demonstrating enhancement of the luminescence of single carbon nanotubes with the help of a random surface of resonant metallic scatterers.
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Deep-UV nitride-on-silicon microdisk lasers
Auteur(s): Selles J., Brimont C., Cassabois G., Valvin P., Guillet T., Roland I., Zeng Y., Checoury X., Boucaud P., Mexis M., Semond F., Gayral B.
(Article) Publié:
Scientific Reports, vol. 6 p.21650 (2016)
Texte intégral en Openaccess :
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DOI: 10.1038/srep21650
WoS: WOS:000370351200001
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45 Citations
Résumé: Deep ultra-violet semiconductor lasers have numerous applications for optical storage and biochemistry. Many strategies based on nitride heterostructures and adapted substrates have been investigated to develop efficient active layers in this spectral range, starting with AlGaN quantum wells on AlN substrates and more recently sapphire and SiC substrates. Here we report an efficient and simple solution relying on binary GaN/AlN quantum wells grown on a thin AlN buffer layer on a silicon substrate. This active region is embedded in microdisk photonic resonators of high quality factors and allows the demonstration of a deep ultra-violet microlaser operating at 275 nm at room temperature under optical pumping, with a spontaneous emission coupling factor $\beta=(4±2) 10^{-4}$. The ability of the active layer to be released from the silicon substrate and to be grown on silicon-on-insulator substrates opens the way to future developments of nitride nanophotonic platforms on silicon.
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Optical properties of hexagonal boron nitride
Auteur(s): Cassabois G., Valvin P., Gil B.
Conférence invité: SPIE Photonics West (San Francisco, US, 2016-02-15)
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Résumé: In this paper, I will review our recent results demonstrating that hBN has an indirect bandgap at 5.9 eV. I will show that the optical properties of hBN are profoundly determined by phonon-assisted transitions with a mirror symmetry between emission and absorption around the indirect exciton at 5.9 eV (Figure 1). I will provide a comprehensive analysis of the emission spectrum in the deep ultraviolet in terms of phonon-assisted transitions involving either virtual or real excitonic states, the latter being provided by structural defects. I will finally point out the complex relaxation dynamics of the quantum gas formed by the reservoir of indirect excitons.
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Unraveling the bandgap nature in hexagonal boron nitride
Auteur(s): Cassabois G.
Conférence invité: UK Nitrides Consortium winter conference (Cambridge, GB, 2016-01-06)
Ref HAL: hal-01281937_v1
Exporter : BibTex | endNote
Résumé: I will discuss our recent experiments by two-photon spectroscopy demonstrating that hBN is an indirect bandgap material. I will show that the optical properties of hBN are profoundly determined by phonon-assisted transitions involving either virtual or real excitonic states. I will present our measurements of the exciton binding energy by two-photon excitation, leading to the estimation of 6.08 eV for the single-particle bandgap in hBN.
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Hexagonal boron nitride is an indirect bandgap semiconductor
Auteur(s): Cassabois G., Valvin P., Gil B.
(Article) Publié:
Nature Photonics, vol. 10 p.262 (2016)
Texte intégral en Openaccess :
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DOI: 10.1038/nphoton.2015.277
WoS: 000372978900017
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476 Citations
Résumé: Hexagonal boron nitride is a wide bandgap semiconductor with a very high thermal and chemical stability used in devices operating under extreme conditions. The growth of high-purity crystals has recently revealed the potential of this material for deep ultraviolet emission, with an intense emission around 215 nm. In the last few years, hexagonal boron nitride has been raising even more attention with the emergence of two-dimensional atomic crystals and Van der Waals heterostructures, initiated with the discovery of graphene. Despite this growing interest and a seemingly simple structure, the basic questions of the bandgap nature and value are still controversial. Here, we resolve this long-debated issue by bringing the evidence for an indirect bandgap at 5.955 eV by means of optical spectroscopy. We demonstrate the existence of phonon-assisted optical transitions, and we measure an exciton binding energy of about 130 meV by two-photon spectroscopy.
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Intraband and intersubband many-body effects in the nonlinear optical response of single-wall carbon nanotubes
Auteur(s): Langlois Benjamin, Parret R., Vialla Fabien, Chassagneux Yannick, Roussignol Philippe, Diederichs Carole, Cassabois G., Lauret Jean‐sébastien, Voisin Christophe
(Article) Publié:
-Physical Review B Condensed Matter And Materials Physics (1998-2015), vol. 92 p.155423 (2015)
Texte intégral en Openaccess :
Ref HAL: hal-01250121_v1
DOI: 10.1103/PhysRevB.92.155423
WoS: 000363013300004
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4 Citations
Résumé: We report on the nonlinear optical response of a mono-chiral sample of (6,5) single-wall carbon nanotubes by means of broad-band two-color pump-probe spectroscopy with selective excitation of the S11 excitons. By using a moment analysis of the transient spectra, we show that all the nonlinear features can be accurately accounted for by elementary deformations of the linear absorption spectrum. The photo-generation of S11 excitons induces a broadening and a blue shift of both the S11 and S22 excitonic transitions. In contrast, only the S11 transition shows a reduction of oscillator strength, ruling out population up-conversion. These nonlinear signatures result from many-body effects, including phase-space filling, wave-function renormalization and exciton collisions. This framework is sufficient to interpret the magnitude of the observed nonlinearities and stress the importance of intersubband exciton interactions. Remarkably, we show that these intersubband interactions have the same magnitude as the intraband ones and bring the major contribution to the photo-bleaching of the S22 excitonic transition upon S11 excitation through energy shift and broadening.
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