GaN-based HFETs demonstrate ubiquitous high power and high frequency performance and attract tremendous research efforts. Even though significant advances have been achieved, there still exist some critical issues needed to be investigated and solved. In particular, high defect densities due to inhomogeneous growth and operation under high power conditions bring many unique problems which are not so critical in the conventional Si and GaAs materials systems. In order to reduce the defect density and heat dissipation of GaN-based HFETs, research work on the realization of GaN-based HFETs on bulk GaN substrate has been carried out and the key problems have been identified and solved. Hot phonon scattering is the bottleneck which limits the enhancement of electron velocity in the GaN 2DEG channel. It is found that the plasmon-phonon coupling is the mechanism for converting of hot phonons into high group velocity acoustic phonons. In order to push more electrons into the GaN 2DEG channel in the plasmon-phonon coupling regime and to further reduce the hot phonon lifetime, a novel AlGaN/GaN dual channel HFET structure has been proposed. The growth, fabrication and characterization of such a AlGaN/GaN dual channel HFET structure has been carried out. Conventionally GaN-based light emitting diodes and laser diodes are grown and fabricated using the c-plane III-nitride expitaxy layers. In c-plane III-nitride epi-layers, the polarization-induced electric field introduces spatial separation of electron and hole wave functions in quantum wells (QW)s used LEDs and laser diodes LDs and degrades quantum efficiency. As well, blueshift in the emission wavelength becomes inevitable with increasing injection current unless very thin QWs are employed. The use of nonpolar orientations, namely, m-plane or a-plane GaN, would solve this problem. So far, m-plane GaN has been obtained on LiAlO2 (100), m-plane SiC substrates, and m-plane bulk GaN, which all have limited availability and/or high cost. Silicon substrates are very attractive for the growth of GaN due to their high quality, good thermal conductivity, low cost, availability in large size, and ease with which they can be selectively removed before packaging for better light extraction and heat transfer when needed To realize the low cost and improve the internal quantum efficiency of GaN based light emitting diodes, the process for m-plane GaN growth on Si (112) substrates has been studied and optimized. The continuous m-plane GaN film is successfully grown on Si (112) substrates.

Dans le but de gérer la consommation et ainsi que la production efficace des énergies renouvelables, l’utilisation et augmentation de l’efficacité des systèmes de conversion d’énergie est devenue indispensable. Dans ce contexte, les transistors en nitrure de gallium (GaN HFETs) pour une densité de puissance commutée très importante, offrent des nouvelles possibilités et ils tirent vers le haut la gestion efficace des énergies renouvelables. Toutefois, cette nouvelle possibilité passe par un pilotage efficace des composants et une encapsulation et des interconnexions optimales. Ces travaux de thèse étudient et analyse les avantages et inconvénients d'une nouvelle structure de conversion multi cellulaire et ceux d’un driver spécifique multivoies monolithique et synchronisé pour les composants GaN, appliqué dans ce contexte précis. Ce manuscrit de thèse est composé de quatre chapitres. Après une étude bibliographique, le positionnement du convertisseur DAB (Dual Active Bridge) parmi les autres structures de conversion DC à l’aide d’une nouvelle méthodologie de comparaison (FOM topologique – Figure de Mérite) est présenté dans le premier chapitre. Afin de diminuer les contraintes de conversion d’énergie, une étude est amenée dans le chapitre 2 sur les principaux défis et enjeux d’une solution générique à travers de réalisation d’un réseau de convertisseurs. Le chapitre 3 présente la partie importante d’expérimentation et d’optimisation de la cellule élémentaire à base de convertisseurs DAB des points de vue fonctionnels mais aussi et surtout structurels. L’étude de l’isolation galvanique de la structure de conversion DAB reste l'objectif principal à développer pour démontrer le potentiel de remplacer le transformateur par une isolation capacitive. La conception de la puce de commande dédiée aux nouveaux transistors GaNs, les résultats pratiques des performances sont présentés dans le dernier chapitre. Certaines comparaisons du driver QGD (Quad Gate Driver) avec les autres solutions de transfert d’ordres de commande sont également discutées. La mise en œuvre du circuit de commande dans un convertisseur DAB afin de valider le fonctionnement de QGD est introduite dans les perspectives. / In order to improve the management and the production efficiency in renewable energy, power electronics systems have become important contributors. In this context, gallium nitride transistors (GaN HFETs) provide new opportunities for high power density, high switching speed and they pull up the effective management of renewable energies. However, this new opportunity requires effective gate drivers and optimal packaging and assembly. This thesis will introduce the general approach of a new architecture for multi cellular conversion and a monolithic multichannel and synchronized drive for GaN components, which are applicable in our specific context. This thesis is composed of four chapters. A bibliographic section is presented in first chapter. A new comparative methodology has been developed in this chapter in order to benchmark the DAB (Dual Active Bridge) converter with respect to other DC converters. In the second chapter, a generic solution (converter grid) has been explained in order to reduce the energy conversion constraints. Chapter 3 presents the important parts of the experimentation and the optimization of DAB converter. High frequency transformer replacing by capacitors is the main objective of this section. The design of the Quad Gate Driver (QGD) IC dedicated to GaNs transistors control in H bridge configuration and the results of their performances are presented in the last chapter. Some comparisons of this approach with other signal transfer solutions are also discussed. The implementation of the QGD in a full bridge transistor converter is introduced into the perspective section.