Boron nitride for excitonics, nano photonics, and quantum technologies

We review the recent progress regarding the physics and applications of boron nitride bulk crystals and its epitaxial layers in various fields. First, we highlight its importance from optoelectronics side, for simple devices operating in the deep ultraviolet, in view of sanitary applications. Emphasis will be directed towards the unusually strong efficiency of the exciton-phonon coupling in this indirect band gap semiconductor. Second, we shift towards nanophotonics, for the management of hyper-magnification and of medical imaging. Here, advantage is taken of the efficient coupling of the electromagnetic field with some of its phonons, those interacting with light at 12 and 6 yin in vacuum. Third, we present the different defects that are currently studied for their propensity to behave as single photon emitters, in the perspective to help them becoming challengers of the NV centres in diamond or of the double vacancy in silicon carbide in the field of modern and developing quantum technologies.This work was financially supported in France by the contract BONASPES (ANR-19-CE30-0007-02) under the umbrella of the publicly funded Investissements d'Avenir program managed by the French ANR agency. This work has been supported in Spain the Spanish MINECO/FEDER under Contracts No. MAT2015-71035-R and No. MAT2016-75586-C4-1-P.Peer reviewe

Overtones of interlayer shear modes in the phonon-assisted emission spectrum of hexagonal boron nitride

We address the intrinsic optical properties of hexagonal boron nitride in deep ultraviolet. We show that the fine structure of the phonon replicas arises from overtones involving up to six low-energy interlayer shear modes. These lattice vibrations are specific to layered compounds since they correspond to the shear rigid motion between adjacent layers, with a characteristic energy of about 6-7 meV. We obtain a quantitative interpretation of the multiplet observed in each phonon replica under the assumption of a cumulative Gaussian broadening as a function of the overtone index, and with a phenomenological line broadening taken identical for all phonon types. We show from our quantitative interpretation of the full emission spectrum above 5.7 eV that the energy of the involved phonon mode is 6.8±0.5 meV, in excellent agreement with temperature-dependent Raman measurements of the low-energy interlayer shear mode in hexagonal boron nitride. We highlight the unusual properties of this material where the optical response is tailored by the phonon group velocities in the middle of the Brillouin zone. © 2017 American Physical Society.Peer reviewe

Leonardo da Vinci y la Música

Sonograma Magazine segueix fent un exercici d'esperança. Subjectivant l'art, pensem que la música, l'art i el pensament poden ajudar-nos en aquests moments d'una crisi de valors en la qual estem immersos. Creiem que la paraula, el so i la imatge són els nostres instruments primordials per comunicar-nos i allunyar- nos d'aquesta apatia que tanta nosa ens fa. Volem retenir tot allò que s'expressa a través de l'art; és per aquest motiu que ampliem les vies d'expressió de la revista Sonograma amb la creació d'una nova secció: La sala d'exposicions. El Suplement de discos, per altra banda, acosta als lectors i lectores a la música produïda al nord d'Europa; compositors i compositores desconeguts en el nostre àmbit musical vénen a enriquir el nostre vocabulari musical amb noves maneres d'expressar-se i, en conseqüència, de compondre. Vivim en un món en constant canvi i cal que ens hi adaptem i que en prenguem consciència. La modernitat líquida (per utilitzar la terminologia de Bauman) ens imposa aquest desig de l'èxit i la riquesa sense límits; ambdós, sostingudes per les modes. Sonograma Magazine sigue haciendo un ejercicio de esperanza. Subjetiva del arte, pensamos que la música, el arte y el pensamiento pueden ayudarnos en estos momentos de una crisis de valores en la que estamos inmersos. Creemos que la palabra, el sonido y la imagen son nuestros instrumentos primordiales para comunicarnos y alejarnos de esta apatía que tanta estorbo nos hace. Queremos retener todo lo que se expresa a través del arte; es por este motivo que ampliamos las vías de expresión de la revista sonograma con la creación de una nueva sección: La sala de exposiciones. El Suplemento de discos, por otra parte, acerca a los lectores a la música producida en el norte de Europa; compositores y compositoras desconocidos en nuestro ámbito musical vienen a enriquecer nuestro vocabulario musical con nuevas maneras de expresarse y, en consecuencia, de componer. Vivimos en un mundo en constante cambio y es necesario que nos adaptamos y que tomemos conciencia. La modernidad líquida (para utilizar la terminología de Bauman) nos impone este deseo del éxito y la riqueza sin límites; ambos, sostenidas por las modas

Electron effective mass and mobility in heavily doped n-GaAsN probed by Raman scattering

We investigate inelastic light scattering by longitudinal optic phonon-plasmon coupled modes LOPCMs in a series of heavily Se-doped, n-type GaAs1−xNx epilayers with x 0.4%. We perform a line shape analysis of the LOPCM spectra to estimate the optical effective mass, mopt , and the scattering time of the conduction electrons in GaAsN. We use these results to evaluate an effective carrier mobility for our samples. The values thus obtained, which we compare with measured electron Hall mobilities, indicate that the x-dependence of the mobility in GaAs1−xNx is dominated by the scattering time, rather than by the variation of the electron effective mass. The Raman analysis yields mopt values that are lower than those obtained from the band anticrossing model. © 2008 American Institute of Physics.This work is supported by the Spanish Government Projects MAT 2004-0664 and MAT2007-63617, and Ramon y Cajal Program and the EPSRC, United Kingdom. 1M. Henini, Dilute Nitride Semiconductors Elsevier Science, AmsterdamPeer reviewe

Far-infrared transmission in GaN,AlN and AlGaN thin films grown by molecular beam epitaxy

We present a far-infrared transmission study on group-III nitride thin films. Cubic GaN and AlN layers and c-oriented wurtzite GaN, AlN, and AlxGa1−xN (x<0.3) layers were grown by molecular beam epitaxy on GaAs and Si(111) substrates, respectively. The Berreman effect allows us to observe simultaneously the transverse optic and the longitudinal optic phonons of both the cubic and the hexagonal films as transmission minima in the infrared spectra acquired with obliquely incident radiation. We discuss our results in terms of the relevant electromagnetic theory of infrared transmission in cubic and wurtzite thin films. We compare the infrared results with visible Raman-scattering measurements. In the case of films with low scattering volumes and/or low Raman efficiencies and also when the Raman signal of the substrate material obscures the weaker peaks from the nitride films, we find that the Berreman technique is particularly useful to complement Raman spectroscop

Long-Lived Phonon Polaritons in Hyperbolic Materials

Natural hyperbolic materials with dielectric permittivities of opposite signs along different principal axes can confine long-wavelength electromagnetic waves down to the nanoscale, well below the diffraction limit. Confined electromagnetic waves coupled to phonons in hyperbolic dielectrics including hexagonal boron nitride (hBN) and α-MoO3 are referred to as hyperbolic phonon polaritons (HPPs). HPP dissipation at ambient conditions is substantial, and its fundamental limits remain unexplored. Here, we exploit cryogenic nanoinfrared imaging to investigate propagating HPPs in isotopically pure hBN and naturally abundant α-MoO3 crystals. Close to liquid-nitrogen temperatures, losses for HPPs in isotopic hBN drop significantly, resulting in propagation lengths in excess of 8 μm, with lifetimes exceeding 5 ps, thereby surpassing prior reports on such highly confined polaritonic modes. Our nanoscale, temperature-dependent imaging reveals the relevance of acoustic phonons in HPP damping and will be instrumental in mitigating such losses for miniaturized mid-infrared technologies operating at liquid-nitrogen temperatures.Research at Columbia is supported by Vannevar Bush Faculty Fellowship ONR-VB: N00014-19-1-2630. We thank A. Sternbach and S. Zhang for helpful discussions. Exfoliation and transfer of hBN onto desired substrates and electron beam lithography of gold disks were performed by J.T.M. and supported by the National Science Foundation (DMR1904793). Additional structure fabrication was supported by the Center on Precision-Assembled Quantum Materials, funded through the U.S. National Science Foundation (NSF) Materials Research Science and Engineering Centers (award no. DMR-2011738). Initial simulations and experimental design from Vanderbilt were provided by J.D.C. in collaboration with the Columbia team (D.N.B. and G.N.) and was supported by the Office of Naval Research (N00014-18-1-2107). The hBN phonon band structure calculation was performed by R.C. and L.A. and supported by the Spanish MINECO/FEDER grant (MAT2015-71035- R). Cryogenics nano-optics experiments at Columbia were solely supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award no. DE-SC0019443. D.N.B is the Gordon and Betty Moore Foundation’s EPiQS Initiative Investigator no. 9455.Peer reviewe

Espectroscopia Raman de semiconductores en GEO3BCN-CSIC

Estudios fundamentales de fonones . Estudio detallado del espectro Raman de primer y segundo orden en cristales de alta calidad; análisis de las simetrías de los modos . Correlación con cálculos ab-initio de las frecuencias y densidad de estados .Espectro de referencia del ZnO (estructura wurtzita

Temperature dependence of Raman-active phonons and anharmonic interactions in layered hexagonal BN

We present a Raman scattering study of optical phonons in hexagonal BN for temperatures ranging from 80 to 600 K. The experiments were performed on high-quality, single-crystalline hexagonal BN platelets. The observed temperature dependence of the frequencies and linewidths of both Raman active E2g optical phonons is analyzed in the framework of anharmonic decay theory, and possible decay channels are discussed in the light of density-functional theory calculations. With increasing temperature, the E2ghigh mode displays strong anharmonic interactions, with a linewidth increase that indicates an important contribution of four-phonon processes and a marked frequency downshift that can be attributed to a substantial effect of the four-phonon scattering processes (quartic anharmonicity). In contrast, the E2glow mode displays a very narrow linewidth and weak anharmonic interactions, with a frequency downshift that is primarily accounted for by the thermal expansion of the interlayer spacing. © 2016 American Physical Society.This work has been financially supported by the Spanish MINECO under Contract No. MAT2015-71035-R. and by the network GaNeX (ANR-11-LABX-0014).Peer reviewe

Isotope effects on the intra- and inter-layer phonons in layered van der Waals crystals: influence on the h-BN phonon lifetimes

9th International Conference on Low Dimensional Structures and Devices in Puerto Varas (Chile), 2-6 December 2019.Research funded by Ministerio de Ciencia, Innovación y Universidades , (MAT2015-71035R

Raman Spectroscopy of Compound Semiconductors

Raman spectroscopy has become a widely used characterization tool in today’s semiconductor research. In this chapter, we provide an introductory background to the physics of Raman scattering and discuss present-day applications of Raman spectroscopy in the field of compound semiconductor physics. Illustrative examples of Raman studies are given on a variety of topics such as crystal quality assessment, strain determination, alloy composition, impurities, and free-charge characterization in doped semiconductors.Peer Reviewe