Étude et optimisation de l'émission et de l'extraction de lumière des nanofils semiconducteurs grand gap : application à des dispositifs électroluminescents

The current blue or white light-emitting diodes (LEDs) are constituted by planar layers of GaN. The use of the nanowires as active layer is a hard and new concept which brings numerous potential advantages and revolutionizes the rules of LED design. This thesis deals with the light emission and extraction of nanowire structures made of wide band gap semi-conductors such as GaN or ZnO. The issue is to understand and to optimize the processes of extraction with the aim of a LED use. We were more particularly interested in three nanowire organizations attractive for the extraction. The first concept concerns nanowires which are enough separated to be considered as isolated. The emission properties of these structures are mainly controlled by the competition between localized resonance (whispering gallery modes) and guided modes which channel and propagate the spontaneous emission towards the nanowires ends. Our second contribution concerns the study of ensembles of small dense nanowires. Goniometry experiments on GaN nanowires made by MBE put in evidence the interest of a nanowires modelling by an effective anisotropic medium. The simulations of the extraction of these devices on silicon substrate are very promising for the creation of efficient and low cost LEDs. Perspectives on nanowires use in periodic organized array so as to realize a photonic crystal are the third part of the thesis. A numerical model allowed suggesting rules of arrays design.Les diodes électroluminescentes (LEDs) bleues ou blanches actuelles sont constituées de couches épitaxiales planaires, essentiellement à base de GaN. Sans autres opérations technologiques, la réflexion totale interne aux interfaces réduit le nombre de photons extraits à quelques pourcents du nombre de photons émis. Cette thèse s'intéresse à un concept en rupture : les LEDs à nanofils GaN ou ZnO. Plus précisément elle vise à préciser l'intérêt de ces couches pour l'augmentation du rendement d'extraction. Nous nous sommes plus particulièrement intéressés à trois types de couches (taille des fils, arrangement), chacune mettant en jeu un processus d'extraction différent. La première géométrie, basée sur des fils relativement gros (rayons 50-100nm minimun) et distants vise à profiter des résonances ou du guidage optique pouvant exister au sein de chaque fil pour canaliser l'émission spontanée. Les coefficients de couplage de la couche active sur ces modes ainsi que la réflectivité des modes guidés en bout de fils ont notamment été évalué numériquement en fonction de la taille des fils. La seconde approche, issue de l'étude goniométrique de couches de fils MBE sur substrat Silicium, vise à profiter des propriétés d'indice effectif des couches de fils sublongueurs d'onde pour éviter le phénomène de réflexion totale à l'origine des faibles rendements d'extraction des couches planaires. Le modèle anisotrope numérique développé montre qu'un rendement d'extraction proche de 70% est envisageable sur ce type de couche épitaxiée sur Silicium. Enfin la troisième approche, plus prospective, vise à initier une étude sur l'émission dans des réseaux de fils agencés périodiquement

Optical properties and resonant cavity modes in axial InGaN/GaN nanotube microcavities

Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers. Disk or tube geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes. In this article we present the fabrication of homogenous and dense arrays of axial InGaN/GaN nanotubes via a combination of displacement Talbot lithography (DTL) for patterning and inductively coupled plasma top-down dry-etching. Optical characterization highlights the homogeneous emission from nanotube structures. Power-dependent continuous excitation reveals a non-uniform light distribution within a single nanotube, with vertical confinement between the bottom and top facets, and radial confinement within the active region. Finite-difference time-domain simulations, taking into account the particular shape of the outer diameter, indicate that the cavity mode of a single nanotube has a mixed WGM-vertical Fabry-Perot mode (FPM) nature. Additional simulations demonstrate that the improvement of the shape symmetry and dimensions primarily influence the Q-factor of the WGMs whereas the position of the active region impacts the coupling efficiency with one or a family of vertical FPMs. These results show that regular arrays of axial InGaN/GaN nanotubes can be achieved via a low-cost, fast and large-scale process based on DTL and top-down etching. These techniques open a new perspective for cost effective fabrication of nano-LED and nano-laser structures along with bio-chemical sensing applications

Apical fibrocavitary lesions of the lung in rheumatoid arthritis

SCOPUS: le.jinfo:eu-repo/semantics/publishe

Hypertension pulmonaire fatale dans un syndrome de Sharp (M.C.T.D.) avec fibrose pulmonaire.

We have followed a case of Mixed Connective Tissue Disease (M.C.T.D.) during 5 years. A progressive pulmonary hypertension inducing cor pulmonary failure terminated in a fatal issue. The prognosis of M.C.T.D. previously considered good is sometimes more severe in spite of immunosuppressive therapy.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

les pleurésies d'hyperstimulation ovarienne.

The syndrome of ovarian hyperstimulation is an exceptional aetiology of pleural effusion. It should be thought of any young women who are under treatment to induce ovulation. The effusions are exudates and not transudates as occurs in Demons-Meigs syndrome. The regression of effusions is usual.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Bronchial cancer and hypereosinophilia

A 73 yr old man with a marked eosinophilia, associated with generalized bronchial carcinoma was observed. Ten months earlier his blood count was normal. The mechanism of eosinophilia is discussed.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

INTERET ET LIMITES DE L'ECHOGRAPHIE EN PNEUMOLOGIE

For a number of valid reasons, echotomography has the reputation of being of little interest in respiratory medicine. Its indications are certainly unfrequent in everyday practice. However, if chest physicians lose interest in the technique, the paradoxal situation may arise where echotomography in respiratory medicine would be under-estimated and under-used. It would be a pity, since the technique is non-invasive and perfectly harmless. The authors review and illustrate the various indications of the method, emphasizing its interest and its limitations.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Épanchement pleural et toxocara canis

SCOPUS: ar.jinfo:eu-repo/semantics/publishe