Advances on MBE selective area growth of III-nitride nanostructures: from nanoLEDs to pseudo substrates

The aim of this work is to provide an overview on the recent advances in the selective area growth (SAG) of (In)GaN nanostructures by plasma assisted molecular beam epitaxy, focusing on their potential as building blocks for next generation LEDs. The first three sections deal with the basic growth mechanisms of GaN SAG and the emission control in the entire ultraviolet to infrared range, including approaches for white light emission, using InGaN disks and thick segments on axial nanocolumns. SAG of axial nanostructures is eveloped on both GaN/sapphire templates and GaN-buffered Si(111). As an alternative to axial nanocolumns, section 4 reports on the growth and characterization of InGaN/GaN core-shell structures on an ordered array of top-down patterned GaN microrods. Finally, section 5 reports on the SAG of GaN, with and without InGaN insertion, on semi-polar (11-22) and non-polar (11-20) templates. Upon SAG the high defect density present in the templates is strongly reduced as indicated by a dramatic improvement of the optical properties. In the case of SAG on nonpolar (11-22) templates, the formation of nanostructures with a low aspect ratio took place allowing for the fabrication of high-quality, non-polar GaN pseudo-templates by coalescence of these nanostructures

Etude de l'hydrogenation photocathodique de Si(p) dans l'acide fluorhydrique HF 5%

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Croissance et propriétés optiques et structurales de nitrures semipolaires (11-22) hétéroépitaxiés sur saphir

Ce travail de thèse concerne la croissance épitaxiale par MOVPE et l étude de nitrures d orientation semipolaire (11-22) sur saphir. Des couches de grande qualité cristalline ont été obtenues en utilisant deux techniques. La première est un procédé original d épitaxie latérale (ELO) : en favorisant la croissance selon [0001], les fautes d empilement sont arrêtées au niveau du joint de coalescence. La seconde technique consiste en l utilisation d un substrat de saphir plan r gravé par voie chimique : la nucléation s effectue au niveau de micro-facette c, ainsi peu de défauts sont créés. Une couche ELO a été étudiée par photoluminescence (PL) et réflectivité en polarisation et en température. Le GaN est polarisé selon [1-100]. Les calculs en théorie k.p ont permis de retrouver les résultats PL. D autre part des couches (In,Ga)N polaires et semipolaires ont été élaborées. L analyse SIMS montre que l incorporation d indium est plus grande dans les couches semipolaires. Ces dernières présentent un fort décalage de Stokes tandis que celui des couches polaires est très faible. Les résultats sur les puits quantiques (In,Ga)N/GaN épitaxiés sur tremplin GaN et GaN ELO montrent que l ELO apporte une amélioration d un facteur 3 sur l intensité d émission, faible en comparaison de la très forte réduction des défauts dans le GaN. Pour des compositions en indium importante, les puits sont polarisés selon [11-2-3], comme le montrent des calculs. Puis des nanostructures de GaN sur (Al,Ga)N émettant dans l UV ont été déposées par épitaxie par jets moléculaires (MBE) sur des tremplins de GaN. Enfin des LEDs semipolaires émettant du vert au rouge ont été étudiées par électroluminescence.NICE-BU Sciences (060882101) / SudocSudocFranceF

Selective heteroepitaxy on deeply grooved substrate: A route to low cost semipolar GaN platforms of bulk quality

Semipolar GaN crystal stripes larger than 100 mu m with dislocation densities below 5 x 10(6) cm(-2) are achieved using a low cost fabrication process. An original sapphire patterning procedure is proposed, enabling selective growth of semipolar oriented GaN stripes while confining the defects to specific areas. Radiative and non-radiative crystalline defects are investigated by cathodoluminescence and can be correlated to the development of crystal microstructure during the growth process. A dislocation reduction mechanism, supported by transmission electron microscopy, is proposed. This method represents a step forward toward low-cost quasi-bulk semipolar GaN epitaxial platforms with an excellent structural quality which will allow for even more efficient III-nitride based devices. Published by AIP Publishing

Freestanding-quality dislocation density in semipolar GaN epilayers grown on SOI: aspect ratio trapping

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Legislative Documents

Also, variously referred to as: House bills; House documents; House legislative documents; legislative documents; General Court documents

Selective growth of tilted ZnO nanoneedles and nanowires by PLD of patterned sapphire substrates

We report the possibility to control the tilting of nanoneedles and nanowires by using structured sapphire substrates. The advantage of the reported strategy is to obtain well oriented growth along a single direction tilted with respect to the surface normal, whereas the growth in other directions is suppressed. In our particular case, the nanostructures are tilted with respect to the surface normal by an angle of 58°. Moreover, we demonstrate that variation of the nanostructures shape from nanoneedles to cylindrical nanowires by using SiO2 layer is observed

Optical properties of small GaN/Al0.5Ga0.5N quantum dots grown on (11-22) GaN templates

GaN-Al0.5NGa0.5N quantum dots deposited on (11-22) planes have been grown by combining Molecular Beam Epitaxy and Metal Organic Vapour Phase Epitaxy. This combination is interesting for realization of ultraviolet operation light emitting diodes, lasers andsingle photon sources,… (1,3) The growth of dots was achieved by MBE using ammonia as nitrogen precursor and growth interruption in ammonia less conditions to trigger corrugation of GaN and dot formation (4). The (11-22) GaN oriented peudosubstrate was realized by MOVPE starting from a M-plane oriented sapphire substrate. The orientation of the growth plane dictates in-plane anisotropies which are effectively found leading to a transition from isolated dots to nanochains - oriented along the direction as evidenced from Atomic Force Microscopy features or optical properties: polarization rates and temperature dependent measurements of the radiative recombination process for instance(5). We here restrict to small size isolated quantum dots and present innovative optical properties among which are micro-photoluminescence data versus pump power, polarization of the emitted photons at different temperatures. We also analyse the photoluminescence decay times and model our finding in the context of the effective mass approximation. The crystal field splitting is measured in Al 0.5NGa 0.5N lattice-matched to (11-2) oriented GaN by polarized microphotoluminecence under high photo- injection conditions

Correlative investigation of Mg doping in GaN layers grown at different temperatures by atom probe tomography and off-axis electron holography

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