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Châteauneuf-Grasse, France

Boichot R.,Grenoble Institute of Technology | Coudurier N.,Grenoble Institute of Technology | Mercier F.,Grenoble Institute of Technology | Claudel A.,ACERDE | And 4 more authors.
Theoretical Chemistry Accounts | Year: 2014

This study presents numerical modeling based on a relatively limited number of gas-phase and surface reactions to simulate the growth rate of aluminum nitride layers on AlN templates and c-plane sapphire in a broad range of deposition parameters. Modeling results have been used to design particular experiments in order to understand the influence of the process parameters on the crystal quality of AlN layers grown in a high-temperature hydride vapor-phase epitaxy process fed with NH3, AlCl3, and H2. Modeling results allow to access to very interesting local quantities such as the surface site ratio and local supersaturation. The developed universal model starting from local parameters might be easily transferred to other reactor geometry and process conditions. Among the investigated parameters (growth rate, temperature, local supersaturation, gas-phase N/Al ratio, and local surface site N/Al ratio), only the growth rate/supersaturation or growth rate/temperature relationships exhibit a clear process window to use in order to succeed in growing epitaxial AlN layers on c-plane sapphire or AlN templates. Gas-phase N/Al ratio and local surface site N/Al ratio seem to play only a secondary role in AlN epitaxial growth. © Springer-Verlag Berlin Heidelberg 2013. Source

Boichot R.,Grenoble Institute of Technology | Claudel A.,ACERDE | Baccar N.,Grenoble Institute of Technology | Milet A.,DCM Chimie Theorique | And 2 more authors.
Surface and Coatings Technology | Year: 2010

AlN growth by HTCVD (High Temperature Chemical Vapor Deposition) from AlCl3 and NH3 is currently a promising way to obtain thick, compact layers of aluminum nitride. This study focused on the development of a kinetic mechanism that models AlN growth with only 7 gas-phase reactions and 4 surface reactions. Ab initio estimation of the thermodynamic data of the AlCl2NH2, AlClNH, AlCl(NH2)2 and Al(NH2)3 intermediates suspected to be involved in the gas-phase reactions is proposed. It was found that only AlCl2NH2 is present in noticeable concentrations under our experimental conditions. Experiments made at different temperatures and N/Al ratios, carried out in a cold wall HTCVD reactor, were used to validate the proposed model. Finally, the N/Al ratio in the gas phase was observed to play a key role in the AlN surface quality. Possible explanations of this influence and future experiments that will confirm this trend are discussed. © 2010 Elsevier B.V. Source

Pons M.,CNRS Materials Science and Engineering | Boichot R.,CNRS Materials Science and Engineering | Coudurier N.,CNRS Materials Science and Engineering | Claudel A.,ACERDE | And 4 more authors.
Surface and Coatings Technology | Year: 2013

The application of AlN films in optoelectronics, sensors and high temperature coatings is strongly dependent on the nano-micro-structure of the film, impurity level and defect density. AlN epitaxial thin (0.5-10μm) and thick polycrystalline (>10μm) films were grown on different foreign substrates (sapphire, silicon carbide, graphite) and single AlN crystals by Chemical Vapor Deposition (CVD), also called Hydride Vapor Phase Epitaxy (HVPE), at high temperature (1200-1750°C). In the first part of this paper, polycrystalline growth of thick films (>10μm) prepared at high growth rate (>100μm·h-1) was performed on graphite substrates to study the preferential orientation of the films. AlN/W multilayers were deposited on silicon carbide composites to increase their performance at high temperature in aggressive conditions. Such multilayer materials can be used for the cladding of nuclear fuel. The second part of this paper concerns the characterization of epitaxial films, including their crystalline state, surface morphology, and inherent and thermally induced stress which inevitably leads to high defect densities and even cracking. The full-width at half-maximum (FWHM) of X-ray rocking curves of the grown AlN layers exhibited very large values (several thousand arcsec), and they became steeply deteriorated with increasing growth rate. To improve the crystalline quality of AlN layer, well-known growth techniques, such as multi-step growth using buffer layers, were used at temperatures above 1200°C in order to lower the disorientation to 300arcsec. The applications of such "templates" for deep UV light emitting diodes (UV LED) and surface acoustic wave sensors (SAW) are discussed. © 2013. Source

Boichot R.,Grenoble Institute of Technology | Coudurier N.,Grenoble Institute of Technology | Mercier F.,Grenoble Institute of Technology | Lay S.,Grenoble Institute of Technology | And 5 more authors.
Surface and Coatings Technology | Year: 2013

AlN is epitaxially grown on c-plane sapphire by High Temperature Hydride Vapor Phase Epitaxy (HT-HVPE) at constant growth rate and thickness, while varying the N/Al ratio in the gas phase at 1500. °C. The influence of an additional low temperature (1200. °C) protective layer on AlN crystal quality is also assessed. The experiments and thermodynamic calculations show that the sapphire substrate is unstable at high temperature under hydrogen and ammonia while it is stable at low temperature or under a few hundred nanometers of AlN protective layer even at high temperature. In terms of AlN crystal quality, the optimal process developed here consists in depositing a 170. nm low temperature protective AlN layer with N/Al=3 followed by a high temperature thick AlN layer grown with N/Al=1.5. In this case, the interface between AlN and sapphire remains continuous (no etching) and the stress in the grown layer at room temperature is minimized by a balance of the growing tensile stress with the cooling compressive stress. © 2013 Elsevier B.V. Source

A process for repairing a damaged annular region of an anode configured to emit x-rays includes the step of machining the damaged annular region made of an initial target coating to a depth smaller than a thickness of the coating so as to leave behind a residual annular layer. An intermediate layer is then deposited on the residual annular layer. A repairing layer is then deposited on the intermediate layer. A heat treatment is then performed using an anneal which causes, by interdiffusion and formation of a solid solution, the material of the intermediate layer and the material of the residual annular layer to diffuse into each other and further cause the material of the intermediate layer and the material of the repairing layer diffuse into each other. As a result of this anneal the intermediate layer disappears.

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