Le projet industriel français MEGaN vise le développement de module de puissance à base de compostant HEMT en GaN. Une des application industrielle concerne l’aéronautique avec une forte contrainte en isolation galvanique (>100 kV/s) et en température ambiante (200°C). Le travail de thèse a été concentré sur une brique module de puissance (bras d’onduleur 650 V 30 A). L’objectif est d’atteindre un prototype de facteur de forme peu épais, 30 cm2 et embarquant l’ensemble des fonctions driver, alimentation de driver, la capacité de bus et capteur de courant phase. Cet objectif implique un fort rendement énergétique, et le respect de l’isolation galvanique alors que la contrainte en surface est forte. Le manuscrit, outre l’état de l’art relatif au module de puissance et notamment celui à base de transistor GaN HEMT, aborde une solution d’isolation de signaux de commande à base de micro-transformateur. Des prototypes de micro-transformateur ont été caractérisés et vieillis pendant 3000 H pour évaluer la robustesse de la solution. Les travaux ont contribué à la caractérisation de plusieurs composants GaN afin de mûrir des modèles pour la simulation circuit de topologie de convertisseur. Au sein du travail collaboratif MEGaN, notre contribution ne concernait pas la conception du circuit intégré (driver de grille), tout en ayant participé à la validation des spécifications, mais une stratégie d’alimentation du driver de grille. Une première proposition d’alimentation isolée pour le driver de grille a privilégié l’utilisation de composants GaN basse-tension. La topologie Flyback résonante avec clamp permet de tirer le meilleur parti de ces composants GaN mais pose la contrainte du transformateur de puissance. Plusieurs technologies pour la réalisation du transformateur ont été validées expérimentalement et notamment une proposition originale enfouissement du composant magnétique au sein d’un substrat polymère haute-température. En particulier, un procédé de fabrication peu onéreux permet d’obtenir un dispositif fiable (1000 H de cyclage entre - 55 ; + 200°C), avec un rendement intrinsèque de 88 % pour 2 W transférés. La capacité parasite d’isolation est réduite par rapport aux prototypes précédent. Deux prototypes d’alimentations à forte intégration utilisent soit les transistors GaN basse tension (2.4 MHz, 2 W, 74 %, 6 cm2), soit un circuit intégré dédié en technologie CMOS SOI, conçu pour l’application (1.2 MHz, 2 W, 77 %, 8.5 cm2). Le manuscrit propose par la suite une solution intégrable de mesure de courant de phase du bras de pont, basé sur une magnétorésistance. La comparaison expérimentale vis à vis d’une solution à résistance de shunt. Enfin, deux prototypes de convertisseur sont décrits, dont une a pu faire l’objet d’une validation expérimentale démontrant des pertes en commutation réduites. / The french industrial project MEGaN targets the development of power module based on GaN HEMT transistors. One of the industrial applications is the aeronautics field with a high-constraint on the galvanic isolation (>100 kV/s) and ambient temperature (200°C). The intent of this work is the power module block (3 phases inverter 650 V 30 A). The goal is to obtain a small footprint module, 30 cm2, with necessary functions such as gate driver, gate driver power supply, bulk capacitor and current phase sensor. This goal implies high efficiency as well as respect of the constraint of galvanic isolation with an optimized volume. This dissertation, besides the state of the art of power modules and especially the GaN HEMT ones, addressed a control signal isolation solution based on coreless transformers. Different prototypes based on coreless transformers were characterized and verified over 3000 hours in order to evaluate their robustness. The different studies realized the characterization of the different market available GaN HEMTs in order to mature a circuit simulation model for various converter topologies. In the collaborative work of the project, our contribution did not focus on the gate driver chip design even if experimental evaluation work was made, but a gate driver power supply strategy. The first gate driver isolated power supply design proposition focused on the low-voltage GaN HEMT conversion. The active-clamp Flyback topology allows to have the best trade-off between the GaN transistors and the isolation constraint of the transformer. Different transformer topolgies were experimentally performed and a novel PCB embedded transformer process was proposed with high-temperature capability. A lamination process was proposed for its cost-efficiency and for the reliability of the prototype (1000 H cycling test between - 55; + 200°C), with 88 % intrinsic efficiency. However, the transformer isolation capacitance was drastically reduced compared to the previous prototypes. 2 high-integrated gate driver power supply prototypes were designed with: GaN transistors (2.4 MHz, 2 W, 74 %, 6 cm2), and with a CMOS SOI dedicated chip (1.2 MHz, 2 W, 77 %, 8.5 cm2). In the last chapter, this dissertation presents an easily integrated solution for a phase current sensor based on the magnetoresistance component. The comparison between shunt resistor and magnetoresistance is experimentally performed. Finally, two inverter prototypes are presented, with one multi-level gate driver dedicated for GaN HEMT showing small switching loss performance.

Les semi-conducteurs à base de composés III-V de type GaN présentent de nombreux avantages – liés essentiellement à leur grande bande interdite - par rapport aux semi-conducteurs traditionnels Si, ou III-V des filières GaAs. De plus, il est possible de former, comme pour les semi-conducteurs traditionnels III-V des hétérojonctions de type HEMT (High Electron Mobility Transistor) AlGaN/GaN permettant d'obtenir à la fois une forte densité de porteurs confinés à l'hétérojonction et des mobilités électroniques élevées. Ces composants sont à l'heure actuelle les candidats les plus prometteurs pour des applications hyperfréquences de puissance. Cependant, l'échauffement observé au cours du fonctionnement et les différentes étapes de réalisation des composants ont un impact anormal sur les performances intrinsèques du composant. La microspectrométrie Raman est une technique nondestructive et sans contact avec une résolution spatiale submicronique, adaptée à l'étude des HEMTs AlGaN/GaN en fonctionnement. L'utilisation de différentes longueurs d'onde excitatrices visible et UV permet de sonder les hétérostructures à différentes profondeurs de pénétration. Les informations obtenues avec cette technique d'analyse sont la composition de l'hétérostructure, les contraintes entre les différentes couches, la résistance thermique aux interfaces, la qualité cristalline des différentes couches, le dopage et le comportement thermique des différentes couches. Le développement d'un système de microspectrométrie Raman UV résolue en temps a permis d'analyser le comportement thermique transitoire des HEMTs AlGaN/GaN en fonctionnement et plus particulièrement dans la zone active du composant.

At present, focus of the SiC crystal growth development is on improving the crystalline quality without polytype inclusions, micropipes and the occurrence of extended defects. The purity of the grown material, as well as intentional doping must be well controlled and the processes understood. High-quality substrates will significantly improve device performance and yield. One of the aims of the thesis is further understanding of polytype inclusion formation as well as impurity control in SiC bulk crystals grown using PVT method also termed seeded sublimation method. Carbonization of the source was identified as a major reason behind the polytype inclusion occurrence during the growth. The aim of this work was further understanding of sublimation growth process of 4H-SiC bulk crystals in vacuum, in absence of an inert gas. For comparison growth in argon atmosphere (at 5 mbar) was performed. The effect of the ambient on the impurity incorporation was studied for different growth temperatures. For better control of the process in vacuum, tantalum as a carbon getter was utilized. The focus of the SiC part of the thesis was put on further understanding of the PVT epitaxy with an emphasis on the high growth rate and purity of grown layers. High resistivity 4H-SiC samples grown by sublimation with high growth rate were studied. The measurements show resistivity values up to high 104 cm. By correlation between the growth conditions and SIMS results, a model was applied in which it is proposed that an isolated carbon vacancy donor-like level is a possible candidate responsible for compensation of the shallow acceptors in p-type 4H-SiC. A relation between cathodoluminescence (CL) and DLTS data is taken into account to support the model. To meet the requirements for high voltage blocking devices such as high voltage Schottky diodes and MOSFETs, 4H-SiC epitaxial layers have to exhibit low doping concentration in order to block reverse voltages up to few keV and at the same time have a low on-state resistance (Ron). High Ron leads to enhanced power consumption in the operation mode of the devices. In growth of thick layers for high voltage blocking devices, the conditions to achieve good on-state characteristics become more challenging due to the low doping and pronounced thicknesses needed, preferably in short growth periods. In case of high-speed epitaxy such as the sublimation, the need to apply higher growth temperature to yield the high growth rate, results in an increased concentration of background impurities in the layers as well as an influence on the intrinsic defects. On-state resistance Ron estimated from current density-voltage characteristics of Schottky diodes on thick sublimation layers exhibits variations from tens of mΩ.cm2 to tens of Ω.cm2 for different doping levels. In order to understand the occurrence of high on-state resistance, Schottky barrier heights were first estimated for both forward and reverse bias with the application of thermionic emission theory and were in agreement with literature reported values. Decrease in mobility with increasing temperature was observed and its dependencies of T–1.3 and T–2.0 for moderately doped and low doped samples, respectively, were estimated. From deep level measurements by Minority Carrier Transient Spectroscopy (MCTS), an influence of shallow boron related levels and D-center on the on-state resistance was observed, being more pronounced in low doped samples. Similar tendency was observed in depth profiling of Ron. This suggests a major role of boron in a compensation mechanism. In the second part of the thesis growth and characterization of GaN is presented. Excellent electron transport properties with high electron saturate drift velocity make GaN an excellent candidate for electronic devices. Especially, AlGaN/GaN based high electron mobility transistors (HEMT) have received an increased attention in last years due to their attractive properties. The presence of strong spontaneous and piezoelectric polarization due to the lattice mismatch between AlGaN and GaN is responsible for high free electrons concentrations present in the vicinity of the interface. Due to the spatial separation of electrons and ionized donors or surface states, 2DEG electron gas formed near the interface of the heterostructure exhibits high sheet carrier density and high mobility of electrons. Al0.23Ga0.77N/GaN based HEMT structures with an AlN exclusion layer on 100 mm semiinsulating 4H-SiC substrates have been grown by hot-wall MOCVD. The electrical properties of the two-dimensional electron gas (2DEG) such as electron mobility, sheet carrier density and sheet resistance were obtained from Hall measurements, capacitance-voltage and contact-less eddy-current techniques. The effect of different scattering mechanisms on the mobility have been taken into account and compared to the experimental data. Hall measurements were performed in the range of 80 to 600 K. Hall electron mobility is equal to 17140 cm2(Vs)-1 at 80 K, 2310 cm2(Vs)-1 at room temperature, and as high as 800 cm2(Vs)-1 at 450 K, while the sheet carrier density is 1.04x1013 cm-2 at room temperature and does not vary very much with temperature. Estimation of different electron scattering mechanisms reveals that at temperatures higher than room temperature, experimental mobility data is mainly limited by optical phonon scattering. At relevant high power device temperature (450 K) there is still an increase of mobility due to the AlN exclusion layer. We have studied the behaviour of Ga-face GaN epilayers after in-situ thermal treatment in different gas mixtures in a hot-wall MOCVD reactor. Influence of N2, N2+NH3 and N2+NH3+H2 ambient on the morphology was investigated in this work. The most stable thermal treatment conditions were obtained in the case of N2+NH3 gas ambients. We have also studied the effect of the increased molar ratio of hydrogen in order to establish proper etching conditions for hot-wall MOCVD growth.

High Electron Mobility Transistoren (HEMTs), basierend auf dem Materialsystem GaN/AlGaN/GaN, wurden entworfen, hergestellt und elektrisch charakterisiert. Für das Maskendesign kam das CAD-Programm LasiCAD zum Einsatz. Das Design umfasste bis zu sechs Lithographieebenen. Die Herstellung der Bauelemente geschah unter Reinraumbedingungen und unter Nutzung einer vorhandenen Technologie für Transistoren mit kleiner Gate-Peripherie (Doppelgate-Transistoren), die teilweise optimiert wurde. Daneben wurden Prozesse zur Herstellung von Multifinger-HEMTs entwickelt, wobei die Metallisierung der Drainkontakte mittels Electroplating von Gold vorgenommen wurde. Zur elektrischen Charakterisierung der Bauelemente wurden sowohl Gleichstromcharakteristiken, d.h. die Ausgangskennlinienfelder und Verläufe der Steilheit, als auch das Großsignalverhalten für cw-Betrieb bei 2 GHz gemessen. Dabei zeigten die Transistoren eine auf die Gatebreite bezogene Ausgangsleistungsdichte von mehr als 8 W/mm und eine Effizienz größer als 40%, einhergehend mit vernachlässigbarer Drainstromdispersion der unpassivierten Bauelemente.

The effect of hot phonons and the influence of macroscopic polarization-induced built-in fields on the performance of III-V nitride devices are investigated. Self-heating due to hot phonons is analyzed in AlGaN/GaN high electron mobility transistors (HEMTs). Thermal transport by acoustic phonons in the diffusive limit is modeled using a two-dimensional lattice heat equation. The effect of macroscopic polarization charges on the operation of blue and green InGaN-based quantum well structures is presented. To characterize these structures, the electronic part of the two-dimensional quantum well laser simulator MINILASE is extended to include nitride bandstructure and material models. A six-band k.p theory for strained wurtzite materials is used to compute the valence subbands. Spontaneous and piezoelectric polarization charges at the interfaces are included in the calculations, and their effects on the device performance are described. Additionally, k.p Hamiltonian for crystal growth directions that minimize the polarization-induced built-in fields are modeled, and valence band dispersion for the non-polar and semi-polar planes are also calculated. Finally, a design parameter subspace is explored to suggest epitaxial layer structures which maximize gain spectral density at a target wavelength for green InxGa1-xN-based single quantum well active regions. The dependence of the fundamental optical transition energy on the thickness and composition of barriers and wells is discussed, and the sensitivity of gain spectral density to design parameters, including the choice of buffer layer material, is investigated.

[Truncated abstract] Over the past decade, the group III-nitride semiconducting compounds (GaN, AlN, InN, and their alloys) have attracted tremendous research efforts due to their unique electronic and optical properties. Their low thermal carrier generation rates and large breakdown fields make them attractive for the development of robust electronic devices capable of reliable operation in extreme conditions, i.e. at high power/voltage levels, high temperatures and in radiation environments. For device applications in radiation environments, such as space electronics, GaN-based devices are expected to manifest superior radiation hardness and reliability without the need for cumber- some and expensive cooling systems and/or radiation shielding. The principle aim of this Thesis is to ascertain the level of susceptibility of current GaN-based elec- tron devices to radiation-induced degradation, by undertaking a detailed study of 60Co gamma-irradiation-induced defects and defect-related effects on the electrical characteristics of n-type GaN-based materials and devices . . . While the irradiation-induced effects on device threshold voltage could be regarded as relatively benign (taking into account that the irradiation levels employed in this study are equivalent to more than 60 years exposure at the average ionising dose rate levels present in space missions), the observed device instabilities and the degradation of gate current characteristics are deleterious effects which will have a significant impact on the performance of AlGaN/GaN HEMTs operating in radiation environments at low temperatures, a combination of conditions which are found in spaceborne electronic systems.

Les matériaux III-N ont apporté un gain considérable au niveau des performances des composants pour les applications en électronique de puissance. Les potentialités majeures du GaN pour ces applications résident dans son grand champ de claquage qui résulte de sa large bande interdite, son champ de polarisation élevé et sa vitesse de saturation importante. Les hétérostructures AlGaN/GaN ont été jusqu’à maintenant le système de choix pour l’électronique de puissance. Les limites sont connues et des alternatives sont étudiées pour les surmonter. Ainsi, les hétérostructures InAlN/GaN en accord de maille ont suscité beaucoup d’intérêts, notamment pour des applications en électronique de puissance à haute fréquence. L’enjeu de ce travail de thèse consiste à élaborer et caractériser des hétérostructures HEMTs (High Electron Mobility Transistors) afin d’établir des corrélations entre défauts structuraux, électriques et procédés de fabrication. Une étude sera donc menée sur la caractérisation de composants AlGaN/GaN afin de cerner les paramètres de croissance susceptibles d’avoir un impact notable sur la qualité structurale et électrique de la structure, notamment sur l’isolation électrique des couches tampons et le transport des porteurs dans le canal. En ce qui concerne les HEMTs InAlN/GaN, l’objectif est d’évaluer la qualité de la couche barrière. Pour cela, une étude de l’influence des épaisseurs ainsi que la composition de la barrière sera menée. La combinaison de ces études permettra d’identifier la structure optimale. Ensuite, l’analyse des contacts Schottky par des mesures de courant et de capacité à différentes températures nous permettra d’identifier les différents modes de conduction à travers la barrière. Enfin, les effets de pièges qui constituent l’une des limites fondamentales inhérentes aux matériaux étudiés seront caractérisés par différentes méthodes de spectroscopie de défauts. / III-N materials have made a significant gain in component performance for power electronics applications. The major potential of GaN for these applications lies in its large breakdown field resulting from its wide bandgap, high polarization field and high electronic saturation velocity. AlGaN/GaN heterostructures have been, until recently, the system of choice for power electronics. The limits are known and alternatives are studied to overcome them. Thus, lattice matched InAlN/GaN heterostructures have attracted a great deal of research interest, especially for high frequency power electronic applications. The aim in this work of thesis consists in developing and in characterizing High Electron Mobility Transistors (HEMTs) to establish correlations between structural, electrical defects and technologic processes. A study will therefore be conducted on the characterization of AlGaN/GaN components to enhance the parameters of growth susceptible to have a notable impact on the structural and electrical quality of the structure, in particular on the electrical isolation of the buffer layers and the transport properties. For InAlN/GaN HEMTs, the objective is to evaluate the quality of the barrier layer. For this, a study of the influence of the thickness as well as the composition of the barrier will be conducted. The combination of these studies will allow identifying the optimum structure. Then, the analysis of Schottky contacts by measurements of current and capacity at different temperatures will allow us to identify the several conduction modes through the barrier. Finally, the effects of traps which constitute one of the fundamental limits inherent to the studied materials will be characterized by various defects spectroscopy methods.

L’intégration monolithique hétérogène de composants III-N sur silicium (Si) offre de nombreuses possibilités en termes d’applications. Cependant, gérer l’hétéroépitaxie de matériaux à paramètres de maille et coefficients de dilatation très différents, tout en évitant les contaminations, et concilier des températures optimales de procédé parfois très éloignées requière inévitablement certains compromis. Dans ce contexte, nous avons cherché à intégrer des transistors à haute mobilité électronique (HEMT) à base de nitrure de Gallium (GaN) sur substrat Si par épitaxie sous jets moléculaires (EJM) en vue de réaliser des circuits monolithiques GaN sur CMOS Si. / The monolithic integration of heterogeneous devices and materials such as III-N compounds with silicon (Si) CMOS technology paves the way for new circuits applications and capabilities for both technologies. However, the heteroepitaxy of such materials on Si can be challenging due to very different lattice parameters and thermal expansion coefficients. In addition, contamination issues and thermal budget constraints on CMOS technology may prevent the use of standard process parameters and require various manufacturing trade-offs. In this context, we have investigated the integration of GaN-based high electron mobility transistors (HEMTs) on Si substrates in view of the monolithic integration of GaN on CMOS circuits.

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