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Optoelectronic properties of hexagonal boron nitride
Auteur(s): Cassabois G.
(Cours Ecole thématique )
, 2019 - , ( RU )Texte intégral en Openaccess :
Ref HAL: cel-02289713_v1
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Résumé: I will discuss here our results on phonon-assisted recombination in hBN, from bulk crystals to few-layer samples. First, I will focus on hBN crystals where the combination of isotopic purification, Raman scattering and polarized-resolved photoluminescence allowed us to identify the different phonon modes involved in the efficient phonon-assisted recombination in bulk hBN. In a second part, I will discuss photoluminescence experiments in epilayers grown by high-temperature molecular beam epitaxy. These epilayers have a thickness of few monolayers of hBN, and I will show that phonon-assisted recombination displays a distinct phenomenology with a PL spectrum different from the one of bulk crystals.
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Hexagonal boron nitride: Physics and Applications in the Deep Ultraviolet
Auteur(s): Cassabois G.
Conférence invité: 13th International Conference on Nitride Semiconductors (ICNS13) (Seattle, US, 2019-07-08)
Ref HAL: hal-02289705_v1
Exporter : BibTex | endNote
Résumé: I will discuss here our results on phonon-assisted recombination in hBN, from bulk crystals to few-layer samples. First, I will focus on hBN crystals where the combination of isotopic purification, Raman scattering and polarized-resolved photoluminescence allowed us to identify the different phonon modes involved in the efficient phonon-assisted recombination in bulk hBN. In a second part, I will discuss photoluminescence experiments in epilayers grown by high-temperature molecular beam epitaxy. These epilayers have a thickness of few monolayers of hBN, and I will show that phonon-assisted recombination displays a distinct phenomenology with a PL spectrum different from the one of bulk crystals.
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Optical properties of hexagonal boron nitride
Auteur(s): Cassabois G.
Conférence invité: International Workshop Spintronics and Valleytronics of Two-dimensional Materials (Daejeon, KR, 2019-05-24)
Ref HAL: hal-02289704_v1
Exporter : BibTex | endNote
Résumé: I will discuss here our results on phonon-assisted recombination in hBN, from bulk crystals to few-layer samples. First, I will focus on hBN crystals where the combination of isotopic purification, Raman scattering and polarized-resolved photoluminescence allowed us to identify the different phonon modes involved in the efficient phonon-assisted recombination in bulk hBN. In a second part, I will discuss photoluminescence experiments in epilayers grown by high-temperature molecular beam epitaxy. These epilayers have a thickness of few monolayers of hBN, and I will show that phonon-assisted recombination displays a distinct phenomenology with a PL spectrum different from the one of bulk crystals.
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Shallow and deep levels in carbon-doped hexagonal boron nitride crystals
Auteur(s): Pelini T., Elias C., Page R., Xue L., Liu S., Li J., Edgar J., Dréau A., Jacques V., Valvin P., Gil B., Cassabois G.
(Article) Publié:
Physical Review Materials, vol. 3 p.094001 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02289672_v1
DOI: 10.1103/PhysRevMaterials.3.094001
WoS: 000483945800001
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34 Citations
Résumé: We study shallow and deep levels in carbon-doped hexagonal boron nitride crystals precipitated from a molten metal solution in a high-temperature furnace. Reflectance and photoluminescence under deep ultraviolet excitation are complemented by spatially resolved experiments by means of a scanning confocal micro-photoluminescence setup operating in the ultraviolet. Isotopically controlled carbon doping does not induce any energy shift of the well-known deep-level emission at 4.1 eV. Our detailed characterization in a series of carbon-doped crystals reveals that the incorporation of carbon during the growth process results in a distinct class of shallow and deep levels in hexagonal boron nitride, calling into question the exact role of carbon in the growth of hexagonal boron nitride and its direct or indirect influence on the formation of the crystal defects.
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Nonreversible Transition from the Hexagonal to Wurtzite Phase of Boron Nitride under High Pressure: Optical Properties of the Wurtzite Phase
Auteur(s): Segura A., Cusco R., Taniguchi T., Watanabe K., Cassabois G., Gil B., Artus L.
(Article) Publié:
The Journal Of Physical Chemistry C, vol. 123 p.20167-20173 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02288999_v1
DOI: 10.1021/acs.jpcc.9b06163
WoS: WOS:000482545700011
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8 Citations
Résumé: We present an infrared reflectance and transmission study of a pressure-induced phase transition of boron nitride from the hexagonal layered structure to the wurtzitic phase. The transition is completed at about 13 GPa. The phase transition is nonreversible and the optical features of the metastable wurtzitic phase are retained after a pressure cycle from 20.5 GPa down to ambient pressure. This allows the infrared-active optical phonons and the dielectric properties of the cold-pressed wurtzitic boron nitride sample to be studied over the whole range of pressures. Experimental permittivity values of ε0 = 6.65 ± 0.03 and ε∞ = 4.50 ± 0.05 are determined from fits to the reflectance spectra at ambient pressure. Accurate values of the refractive index in the mid-infrared and visible–ultraviolet regions are evaluated from the interference patterns. Contrary to the h-BN case, the refractive index of w-BN decreases slightly with pressure, on account of the much lower compressibility of the close-packed structure. The pressure coefficients for the longitudinal optical and transverse optical modes are determined, and an overall good agreement with ab initio calculations is found.
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Effects of isotopic substitution on the phonons of van der Waals crystals: the case of hexagonal boron nitride
Auteur(s): Cusco R., Edgar J., Liu S., Cassabois G., Gil B., Artus L.
(Article) Publié:
Journal Of Physics D: Applied Physics, vol. 52 p.303001 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02288990_v1
DOI: 10.1088/1361-6463/ab1cab
WoS: WOS:000468875700001
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5 Citations
Résumé: The recent availability of isotopically pure samples of hexagonal boron nitride (h-BN) has allowed the isotopic substitution effects to be studied in this highly interesting layered crystal. Here, we review the application of Raman scattering to investigate phonon anharmonic decay and its particularities in layered crystals, exemplified by h-BN. The modification of the phonon spectrum and anharmonic phonon decay paths in isotopically pure samples is specifically addressed. Detailed information about phonon lifetimes and decay channels is obtained for h-BN from a thorough analysis of temperature-dependent Raman scattering measurements in the light of density functional theory and perturbation theory calculations. The phonon lifetime is substantially increased in isotopically pure crystals, which may have important implications for the development of low-loss h-BN based phonon-polariton devices. On account of the low cation mass, isotopic substitution substantially alters the dominant phonon decay pathways and changes the strength of phonon anharmonic interactions.
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High-Pressure Softening of the Out-of-Plane A2u(Transverse-Optic) Mode of Hexagonal Boron Nitride Induced by Dynamical Buckling
Auteur(s): Segura A, Cusco R., Taniguchi T., Watanabe Kanji, Cassabois G., Gil B., Artus L.
(Article) Publié:
The Journal Of Physical Chemistry C, vol. 123 p.17491 (2019)
Texte intégral en Openaccess :
Ref HAL: hal-02192575_v1
DOI: 10.1021/acs.jpcc.9b04582
WoS: 000476693800050
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6 Citations
Résumé: We investigate the highly anisotropic behavior of the in-plane and out-of-plane infrared-active phonons of hexagonal boron nitride by means of infrared reflectivity and absorption measurements under high pressure. Infrared reflectivity spectra at normal incidence on high-quality single crystals show strict fulfillment of selection rules and an unusually long E1u[transverse-optic (TO)] phonon lifetime. Accurate values of the dielectric constants at ambient pressure ε⊥0 = 6.96, ε⊥∞ = 4.95, ε∥0 = 3.37, and ε∥∞ = 2.84 have been determined from fits to the reflectivity spectra. The out-of-plane A2u phonon reflectivity band is revealed in measurements on an inclined facet, and absorption measurements at an incidence angle of 30° allow us to observe both the transverse- and longitudinal-optic A2u modes. Pressure coefficients and Grüneisen parameters for all infrared-active modes are determined and compared with ab initio calculations. While Grüneisen parameters are generally small in this layered crystal, the A2u(TO) displays an exceptionally large and negative Grüneisen parameter that results in widening of the type I hyperbolic region with increasing pressure. Softening of the A2u(TO) mode is induced by dynamical buckling of the flat honeycomb layers.
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