Croissance de semi-conducteurs à grand gap

La modélisation et la simulation des procédés de croissance tel que le transport physique en phase vapeur (PVT), le dépôt chimique en phase vapeur (CVD ou HTCVD) et les techniques hybrides (CFPVT), sont suffisamment au point pour être utilisées comme des outils de compréhension des phénomènes physiques couplés et comme des outils de conception de nouveaux procédés et d'optimisation de procédés existants. La modélisation des procédés d'élaboration rassemble plusieurs voies physico-chimiques de complexité variable, depuis des études thermodynamiques et/ou cinétiques jusqu'aux transferts simultanés de matière et de chaleur couplées avec les bases de données et propriétés thermodynamiques et/ou cinétiques et de transport. Différentes voies de modélisation sont utilisées, thermodynamiques, cinétique ou transfert de masse, de façon couplée ou découplée, permettant de visualiser l'évolution de la croissance et ainsi comprendre le rôle complexe et fortement couplé des phénomènes

Contribution à la modélisation bidimentionnelle et tridimentionnelle des phénomènes d'anisotropie dans les transformateurs triphasés

We present in this thesis, our contribution to the modeling of anisotropy phenomena in circuits magnetic transformers. These phenomena are of 2 kinds, firstly the crystalline anisotropy of the sheets with oriented crystals and secondly the geometric anisotropy or "pseudo anisotropy", related to the lamination of the transformers. Different mathematical models for the representation of materials with non-linear anisotropic characteristics are proposed and analyzed. A general technique for homogenizing heterogeneous materials with periodic structures has been developed. This technique called the iron-air lamination method of transformers.Nous présentons dans ce mémoire, notre contribution à la modélisation des phénomènes d'anisotropie dans les circuits magnétiques des transformateurs. Ces phénomènes sont de 2 sortes, tout d'abord l'anisotropie cristalline des tôles à cristaux orientés et d'autre part l'anisotropie géométrique ou "pseudo anisotropie", liée au feuilletage des transformateurs. Différents modèles mathématiques pour la représentation des matériaux à caractéristiques anisotropiques non linéaires sont proposés et analysés. Une technique générale permettant d'homogénéiser des matériaux hétérogènes à structures périodiques a été développée. Cette technique appelée méthode des moyennes au feuilletage fer-air des transformateurs

Numerical modeling of flow focusing: Quantitative characterization of the flow regimes

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Contribution a la modelisation bidimensionnelle et tridimensionnelle des phenomenes d'anisotropie dans les transformateurs

SIGLEINIST T 71089 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

A Three Dimensional Electrical Model of SOFC Stack

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Analysis of Macrostep Formation during Top Seeded Solution Growth of 4H-SiC

International audienceWe used numerical and analytical modeling to investigate fluid flow behaviors close to the growing 4H-SiC crystal surface in the top seeded solution growth process. First, we calculated the azimuthal and radial components of the fluid flow in front of the rotation disc. Second, we developed an analytical model describing the interaction between the step flow (of the vicinal crystal surface) and fluid flow components, considering the crystallography of 4H-SiC and introducing a phase parameter. The correlation of both models allows us to describe qualitatively the conditions for which macrosteps form and destabilize. This phenomenological description is in good agreement with the corresponding experimental observations that are also presented in this paper

Optimisation d'un procédé de vitrification chauffé par induction directe par couplage des simulations électromagnétique et Thermo-hydrodynamique

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Comparison of Thermodynamic Databases for the Modeling of SiC Growth by PVT

International audienceThe numerical modeling of the SiC bulk growth process by physical vapor transport has been established as the essential tool for the process development. An accurate computation of mass transfers is strongly dependent on the equilibrium partial pressure calculations. In this paper, we compare the relative impact of the different thermodynamic databases available on the full PVT process modeling. We found that whatever the database used, the trends regarding growth rate calculation, crystal shape, Si/C ratio are correctly described and none of the database would bring about unacceptable errors from the process development point of view even if some discrepancies in the absolute values could be obtained

A first step toward bridging silicon carbide crystal properties and physical chemistry of crystal growth

International audienceThe links between the occurrence of a given silicon carbide (SiC) polytype and crystal growth conditions have been mainly empirically described. Although studies are a little more advanced, a similar description can be applied to point defects and especially dopants in the crystals. We propose a method to determine such links, based on a coupled thermodynamic and mass transport model, where SiC is treated as a solid solution. We implemented such an approach to the case of the seeded sublimation growth process, which is currently the industrial bulk growth process for SiC single crystalline ingots. The computation of both Si and C activities in the SiC crystal, between the SiC-C and SiC-Si two-phase equilibria, allowed first the assessment of the SiC crystal chemistry and second the linking of SiC-C and SiC-Si chemistry with the growth process parameters. We demonstrate that depending on the temperature, pressure and a temperature gradient, the activities of Si and C in the crystals can be described and tuned. The case of cubic polytype (3C-SiC) formation is specifically discussed. Its stabilization requires a high Si activity and a low C activity in the SiC crystal, meaning that the synthesis conditions must be close to the limit at the SiC + Si phase boundary

Capillary Oscillations in the Transient Mode of Flow Focusing: Comparison Between Experimental measurements and Numerical Results

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