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Optical study of GaN nanowires and GaN/AlN microcavities

Jeudi 15 novembre 2012 14:00 - Duree : 1 heure
Lieu : Amphithéâtre du bâtiment A, Institut Néel, CNRS - 25 rue des Martyrs - 38000 Grenoble

Orateur : Soutenance de Diane SAM-GIAO (CEA-Grenoble – INAC/SP2M/NPSC)

This work focuses on the optical study of GaN nanowires and AlN microcavities containing GaN quantum dots. The 1-meV linewidth of the neutral donor-bound exciton line in the photoluminescence spectrum of MBE-grown GaN nanowires evidences that the strain is homogeneous in the material. These nanowires do not exhibit any excitonic confinement, but the efficient strain relaxation allows to grow strain-free zinc-blende GaN nanowires and then to conduct fine spectroscopy on the cubic GaN near band edge. Besides, we show that the tentative attribution of the recombination line at 3.45 eV in the spectrum of wurtzite GaN nanowires to a surface-enhanced two-electron satellite does not hold. Indeed, its dipole polarization selection rules and its evolution with intense applied magnetic field do not match that of a two-electron satellite.

We also performed the spectroscopy of GaN/AlN quantum dot microdisks. Record quality factors for AlN cavities were measured around 3 eV. GaN/AlN quantum dot nanocavities embedded in photonic crystal waveguides were also investigated. The attribution of each mode either to the waveguide or to the cavity, predicted by calculations, is experimentally confirmed by a different light localization. These structures allow excellent quality factors to be reached, from 2300 at 3.45 eV, up to 4400 at 3.14 eV. Although the expected Purcell factor is very high (around 100), we did not manage to observe the Purcell effect. This originates either from an enhancement of non-radiative recombination channels or from an instability of both the cavity modes and the quantum dot emission under intense exposure. Finally, it appears that the main limiting factor to achieve lasing in these structures is the strong built-in electric field, which slows up the spontaneous emission rate of the quantum dots.

Le jury sera composé de : Pierre Lefebvre (rapporteur), Joël Leymarie (rapporteur), Sophie Bouchoule, Raphaël Butté, David Ferrand, Bruno Gayral (directeur de thèse)

Contact : carmelo.castagna@cea.fr

Discipline évènement : (Physique)
Entité organisatrice : (INAC/SP2M)
Nature évènement : (Soutenance de thèse)
Site de l'évènement : Polygone scientifique

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