Time series as data in the machine learning research area has been dominated by prediction and forecasting techniques. Ever since the inception of generative models, the interest in generating time series has increased. Time series data appears in many different fields with financial and medical gathering much of the interest. This thesis is instead focusing on the automotive field with a heavy focus on wheel speed data. The issue with wheel speed data, or any other vehicle signal, is that they take a long time to gather since a person has to drive around in order to get the data.  This thesis investigates the possibility to generate vehicle signals with a large focus on wheel speed signals. To better understand the difference between different car models and which vehicle signals are most useful. The classification of vehicle time series was done with a stacked LSTM network. A thorough analysis of the network parameters was made and an accuracy of over 80\% was achieved when classifying 6 different vehicle models. For time series generation a GAN with LSTM networks was used, based on CRNNGAN. The generated samples were evaluated by people experienced with the data and by using both PCA and t-SNE. The result is bad and is too noisy. Only one of the vehicle signals could be generated in a satisfying manner and that signal was significantly less complex since it was a binary signal being either 0 or 1.

Advanced achievements in the area of RF circuit design led to a significant increase in availability of wireless communications in everyday life. However, the rapid growth in utilizing the RF equipment has brought several challenges in different aspects of RF circuit design. This has been motivating researchers to introduce solution to cope with these challenges and further improve the performance of the RF circuits. In this dissertation, we focus on the improvements in three aspects of the circuit design. High temperature and temperature compensated transmitter design, ultra-low phase noise signal generators, and compact and low complexity polar transmitter design. Increase in the ambient temperature can impact the performance of the entire communication system. However, the RF hardware is main part of the system that is under the impact of the temperature variations in which it can change the characteristics of the individual building blocks of the RF chain. Moreover, transistors are the main elements in the circuit whose performance variation must be consider when the design target is compensating the temperature effects. The influence of the temperature variation is studied on the transistors and the building blocks in order to find the most effective approaches to compensate these variations and stabilize the performance of the RF chain at temperatures up to 220 C. A temperature sensor is designed to sense these variations and adjust the characteristics of the circuit components (e.g. bias voltages), accordingly. Further, a new variable gain phase shifter (VGPS) architecture is introduced toward minimizing the temperature impact on its performance in a phased-array transmitter architecture. Finally, a power amplifier as the last stage in a transmitter chain is designed and the variation in its performance with temperature is compensated through the VGPS stage. The transmitter is prototyped to evaluate its performance in practice. Another contribution of this dissertation is to introduce a novel voltage-controlled oscillator (VCO) structure to reduce the phase noise level below state-of-the-art. The noise to phase noise mechanism in the introduced doubly tuned oscillator is studied using linear time-variant (LTV) theory to identify the dominant noise sources and either eliminate or suppress these noise sources by introducing effective mechanism such as impedance scaling. The designed VCO is fabricated and measurement results are carried out that justified the accuracy of the analyses and effectiveness of the introduced design approach. Lastly, we introduce a compact and simple polar transmitter architecture. This type of transmitters was firstly proposed to overcome the serious shortcomings in the IQ transmitters, such as IQ imbalance and carrier leakage. However, there is still several challenges in their design. We introduce a transmitter architecture that operates based on charge to phase translation mechanism in the oscillator. This leads to significantly reduction in the design complexity, die area, and power dissipation. Further, it eliminates a number of serious issues in the design such as sampling rate of the DACs. comprehensive post-layout simulations were also performed to evaluate its performance. / Doctor of Philosophy / To keep up with the ever-growing demand for exchanging information through a radio frequency (RF) wireless network, the specification of the communication hardware (i.e. transmitter and receiver) must be improved as the bottleneck of the system. This has been motivating engineers to introduce new and efficient approaches toward this goal. In this dissertation however, we study three aspects of the circuit design. First, variation in the ambient temperature can significantly degrade the performance of the communication system. Therefore, we study these variations on the performance of the transmitter at high temperature (i.e. above 200 C). Then, the temperature compensation approaches are introduced to minimize the impact of the temperature changes. The effectiveness of the introduced techniques are validated through measurements of the prototyped transmitter. Second, signal generators (i.e. oscillators) are the inseparable blocks of the transmitters. Phase noise is one of the most important specifications of the oscillators that can directly be translated to the quality and data rate of the communication. A new oscillator structure targeting ultra-low phase noise is introduced in the second part of this dissertation. The designed oscillator is fabricated and measured to evaluate its performance. Finally, a new polar transmitter architecture for low power applications is introduced. The transmitter offers design simplicity and compact size compared to other polar transmitter architectures while high performance.

Interest in wide bandgap semiconductors such as silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga 2 O 3 ) and diamond has increased due to their ability to deliver high power, high switching frequency and low loss electronic devices for power conversion applications. To meet these requirements, semiconductor material defects, introduced during growth and fabrication, must be minimized. Otherwise, theoretical limits of operation cannot be achieved. In this dissertation, the non-ideal current- voltage (IV) behavior of GaN-based Schottky diodes is discussed first. Here, a new model is developed to explain better the temperature dependent performance typically associated with a multi-Gaussian distribution of barrier heights at the metal-semiconductor interface [Section 3.1]. Application of this model gives researches a means of understanding not only the effective barrier distribution at the MS interface but also its voltage dependence. With this information, the consequence that material growth and device fabrication methods have on the electrical characteristics can be better understood. To show its applicability, the new model is applied to Ru/GaN Schottky diodes annealed at increasing temperature under normal laboratory air, revealing that the origin of excess reverse leakage current is attributed to the low-side inhomogeneous barrier distribution tail [Section 3.2]. Secondly, challenges encountered during MOCVD growth of low-doped GaN drift layers for high-voltage operation are discussed with focus given to ongoing research characterizing deep-level defect incorporation by deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) [Section 3.3 and 3.4]. It is shown that simply increasing TMGa so that high growth rates (>4 µm/hr) can be achieved will cause the free carrier concentration and the electron mobilities in grown drift layers to decrease. Upon examination of the deep-level defect concentrations, it is found that this is likely caused by an increase in 4 deep level defects states located at E C - 2.30, 2.70, 2.90 and 3.20 eV. Finally, samples where the ammonia molar flow rate is increased while ensuring growth rate is kept at 2 µm/hr, the concentrations of the deep levels located at 0.62, 2.60, and 2.82 eV below the conduction band can be effectively lowered. This accomplishment marks an exciting new means by which the intrinsic impurity concentration in MOCVD-grown GaN films can be reduced so that >20 kV capable devices could be achieved. / Doctor of Philosophy / We constantly rely on electronics to help assist us in our everyday lives. However, to ensure functionality we require that they minimize the amount of energy lost through heat during operation. One contribution to this inefficiency is incurred during electrical power conversion. Examples of power conversion include converting from the 120 V wall outlet to the 5 V charging voltage used by cellphones or converting the fluctuating voltage from a solar panel (due to varying sun exposure) to the 120 V AC power found in a typical household. Electrical circuits can be simply designed to accomplish these conversions; however, consideration to every component must be given to ensure high efficiency. A popular example of an electrical power conversion circuit is one that switches the input voltage on and off at high rates and smooths the output with an inductor/capacitor network. A good analogy of this process is trying to create a small stream of water from a fire hydrant which can either be off or on at full power. Here we can use a small cup but turning the fire hydrant on and trying to fill the cup will destroy it. However, if the fire hydrant is pulsed on and off at very short intervals (1 µs), its possible to fill the cup without damaging it or having it overflow. Now, under ideal circumstances if a small hole is poked in the bottom of the cup and the interval of the fire hydrant is timed correctly, a small low power stream of water is created without overflowing the cup and wasting water. In this analogy, a devices capable of switching the stream of water on and off very fast would need to be implemented. In electrical power conversion circuits this device is typically a transistor and diode network created from a semiconducting material. Here, similar to the fire hydrant analogy, a switch would need to be capable of holding off the immense power when in the off position and not impeding the powerful flow when in the on position. The theoretical limit of these two characteristics is dependent on the material properties of the switch where typically used semiconductors include silicon (Si), silicon carbide (SiC), or gallium nitride (GaN). Currently, GaN is considered to be a superior option over Si or SiC to make the power semiconductor switching device, however research is still required to remove non-ideal behavior that ultimately effects power conversion efficiency. In this work, we first examine the spurious behavior in GaN-based Schottky diodes and effectively create a new model to describe the observed behavior. Next, we fabricated Ru/GaN Schottky diodes annealed at different temperatures and applied the model to explain the room-temperature electrical characteristics. Finally, we grew GaN under different conditions (varying TMGa and ammonia) so that quantum characteristics, which have been shown to affect the overall ability of the device, could be measured.

Group III-nitride semiconductors are well suited for the fabrication of devices including visible-ultraviolet light emitting diodes, high-temperature and high-frequency devices. The wurtzite III-nitride based heterostructures grown along polar c-direction have large internal electric fields due to discontinuities in spontaneous and piezoelectric polarizations. For optoelectronic devices, such as light-emitting diodes and laser diodes, the internal electric field is deleterious as it causes a spatial separation of electron and hole wave functions in the quantum wells, which decreases emission efficiency. Growth of GaN-based heterostructures in alternative orientations, which have reduced (semipolar) or no polarization (nonpolar) in the growth direction, has been a major area of research in the last few years. The correlation between structural, optical and transport properties of semipolar and nonpolar III-nitride would be extremely useful. The thesis focuses on the growth and characterizations of semipolar and nonpolar III-nitride heterostructures by plasma-assisted molecular beam epitaxy. Chapter 1 provides a brief introduction to the III-nitride semiconductors. The importance of semipolar and nonpolar III-nitride heterostructures over conventional polar heterostructures has been discussed. Chapter 2 deals with the descriptions of molecular beam epitaxy system and working principles of different characterization tools used in the present work. Chapter 3 addresses the molecular beam epitaxial growth of nonpolar (1 1 -2 0) and semipolar (1 1 -2 2) GaN on sapphire substrates. An in-plane orientation relationship is found to be [0 0 0 1] GaN || [-1 1 0 1] sapphire and [-1 1 0 0] GaN || [1 1 -2 0] sapphire for nonpolar GaN on r-sapphire substrates. Effect of growth temperature on structural, morphological and optical properties of nonpolar GaN has been studied. The growth temperature plays a major role in controlling crystal quality, morphology and emission properties of nonpolar a-plane GaN. The a-plane GaN shows crystalline anisotropy nature and it has reduced with increase in the growth temperature. The surface roughness was found to decrease with increase in growth temperature and film grown at 760°C shows reasonably smooth surface with roughness 3.05 nm. Room temperature photoluminescence spectra show near band emission peak at 3.434 -3.442 eV. The film grown at 800 ºC shows broad yellow luminescence peak at 2.2 eV. Low temperature photoluminescence spectra show near band emission at 3.483 eV along with defect related emissions. Raman spectra exhibit blue shift due to compressive strain in the film. An in-plane orientation relationship is found to be [1 -1 00] GaN || [1 2-1 0] sapphire and [-1 -1 2 3] GaN || [0 0 0 1] sapphire for semipolar GaN on m-plane sapphire substrates. The surface morphology of semipolar GaN film is found to be reasonably smooth with pits on the surface. Room temperature photoluminescence shows the near band emission (NBE) at 3.432 eV, which is slightly blue shifted compared to the bulk GaN. The Raman E2 (high) peak position observed at 569.1 cm1. Chapter 4 deals with the fabrication and characterizations of Au/nonpolar and Au/semipolar GaN schottky diodes. The temperature-dependent current–voltage measurements have been used to determine the current mechanisms in Schottky diodes fabricated on nonpolar a-plane GaN and semipolar GaN epilayers. The barrier height (φb) and ideally factor (η) estimated from the thermionic emission model are found to be temperature dependent in nature indicate the deviations from the thermionic emission (TE) transport mechanism. Low temperature I-V characteristics of Au/ GaN Schottky diode show temperature independent tunnelling parameter. Barrier heights calculated from XPS are found to be 0.96 eV and 1.13 eV for Au/nonpolar GaN and Au/semipolar GaN respectively. Chapter 5 demonstrates the growth of InN on r-sapphire substrates with and without GaN buffer layer. InN film and nanostructures are grown on r-sapphire without GaN buffer layer and they are highly oriented along (0002) direction. The electron microscopy study confirms the nanostructures are vertically aligned and highly oriented along the (0001) direction. The Raman studies of InN nanostructures show the SO modes along with the other possible Raman modes. The band gap of InN nanostructures is found to be 0.82 eV. InN grown with a-plane GaN buffer shows nonpolar orientated growth. Growth temperature dependent studies of nonpolar a-plane InN epilayers are carried out. The valence band offset value is calculated to be 1.31 eV for nonpolar a-plane InN/GaN heterojunctions. The heterojunctions form in the type-I straddling configuration with a conduction band offsets of 1.41 eV. Chapter 6 deals with the temperature dependent I-V characteristics of the nonpolar a-plane (1 1 -2 0) InN/GaN heterostructures. The measured values of barrier height and ideality factor from the TE model show the temperature dependent variation. The double Gaussian distribution has mean barrier height values ( ϕb ) of 1.17 and 0.69 eV with standard deviation (σs ) of 0.17 and 0.098 V, respectively. The modified Richardson plot ln (Is/T2)-q2σ2/2k2T2 ) versus q/kT in the temperature range of 350 – 500 K, yielded the Richardson constant of 19.5 A/cm2 K2 which is very close to the theoretical value of 24 A/cm2 K2 for n-type GaN. The tunneling parameters E0 found to be temperature independent at low temperature range (150 –300 K). Chapter 7 concludes with the summary of present investigations and the scope for future work.

Les fortes capacités actuelles et envisagées des futurs liens satellites de communication pour la 5G conduisent les signaux traités dans les charges utiles à présenter simultanément d'importantes variations d'amplitude (PAPR>10dB) et de très larges bandes passantes instantanées (BW>1GHz). A l'intérieur du sous-système d'émission hyperfréquence, le fonctionnement du module d'amplification de puissance se trouve très contraint par les formes d'ondes véhiculées, il se présente comme l'un des postes de consommation énergétique des plus importants, et ayant le plus d'impact sur l'intégrité du signal émis. Dans ce contexte, les fonctions dédiées au traitement numérique des signaux et couramment implémentées par le processeur numérique (telles que le filtrage, la canalisation, et éventuellement la démodulation et la régénération des signaux bande de base) embarquées dans les charges utiles, représentent une solution à fort potentiel qui permettrait de relâcher les contraintes reportées sur la fonction d'amplification de puissance afin de gérer au mieux la ressource électrique allouée. Ces travaux de thèse proposent d'étudier les potentialités d'amélioration du fonctionnement en rendement et linéarité d'un amplificateur de type Doherty à double entrée de gamme 20W en technologie GaN et fonctionnant en bande C. La combinaison des signaux de puissance sur la charge RF est optimisée par une distribution optimale des signaux en amplitude et phase à l'entrée par des moyens numériques de génération. Dans un premier temps une méthodologie de conception large bande d'un amplificateur Doherty est introduite et validée par la conception d'un démonstrateur en bande C. Dans un second temps, l'outil expérimental permettant l'extraction des lois optimales de distribution d'amplitude et de phase RF est présenté en détail, et la caractérisation expérimentale du dispositif en double entrée est réalisée puis comparée aux simulations. Finalement, en perspective à ces travaux, une étude préliminaire des potentialités de l'architecture Doherty à double entrée pour la gestion d’une désadaptation de la charge de sortie (gestion de TOS) est menée et des résultats sont mis en avant. / The high capabilities of current and future 5G communication satellite links lead the processed signals in the payloads to simultaneously exhibit large amplitude variations (PAPR>10dB) and wide instantaneous bandwidths (BW>1GHz). Within the microwave transmission subsystem, the operation of the power amplification stage is highly constrained by the transmitted waveforms, it is one of the most energy-consuming module of the payload affecting as well the integrity of the transmitted signal. In this context, the functions dedicated to digital signal processing and currently implemented by the digital processor (such as filtering, channeling, and possibly the demodulation and regeneration of baseband signals) embedded in the payloads, represent a potential solution that would reduce the constraints reported on the power amplification function and help to manage the allocated power ressource. This work proposes a study on the capability of dual input power amplifier architectures in order to manage the efficiency-linearity trade-off over a wide bandwidth. This study is carried out on a 20W GaN Doherty demonstrator operating in C band. The combination of the output signals on the RF load is managed by an optimal amplitude and phase distribution that is digitally controlled at the input. Firstly, a wideband design methodology of Doherty amplifier is introduced and validated on a C band demonstrator. In a second time the experimental tool allowing the extraction of amplitude and phase input distributions is presented, the dual input characterization is achieved and compared with simulation results. Finally, in perspective of this work, a preliminary study of the capabilities of the digital Doherty for the management of an output load mismatch (VSWR management) is carried out and the results are put forward.

Résumé: Parmi les technologies du 21e siècle en pleine expansion, la télécommunication sans-fil constitue une dimension fondamentale pour les réseaux mobiles, l’aéronautique, les applications spatiales et les systèmes de positionnement par satellites. Les nouveaux défis à surmonter sont à la fois l’augmentation des distances de transmission associée à l’accroissement des quantités de données véhiculées ainsi que la miniaturisation, la réduction du coût de production, la moindre consommation énergétique et la fiabilité de la solution technologique employée pour la chaîne de transmission. Dans ce sens, l’exploitation de bandes de plus hautes fréquences et la multiplication des canaux de transmission sont activement visées par les travaux de recherches actuels. Les technologies à l’étude reposent sur l’utilisation de systèmes intégrés pour répondre aux considérations de coûts de fabrication et d’encombrement. L’élément de base de ces systèmes, le transistor, établit largement la performance du dispositif final en termes de montée en fréquence, de fiabilité et de consommation. Afin de répondre aux défis présents et futurs, des alternatives à la filière silicium sont clairement envisagées. À ce jour, la filière nitrure de gallium est présentée comme la plus prometteuse pour l’amplification de puissance en bande Ka et W au vu de ses caractéristiques physiques et électriques, des performances atteintes par les prototypes réalisés et des premiers produits commerciaux (off-the-shelf) disponibles. L’exploitation de cette technologie à son plein potentiel s’appuie particulièrement sur la maîtrise des étapes de fabrication, de caractérisation et de modélisation du transistor. Ce travail de thèse a pour objectif le déploiement d’une méthodologie permettant la modélisation semi-physique de transistors fabriqués expérimentalement et démontrant des performances à l’état de l’art. Une partie conséquente de ce travail portera sur la caractérisation thermique du dispositif en fonctionnement ainsi que sur la modélisation d’éléments secondaires (éléments passifs) pour la conception d’un circuit amplificateur hyperfréquence. / Abstract: Amongst the emerging and developing technologies of the 21st century, wireless transmission is a fundamental aspect for mobile networks, aeronautics, spatial applications and global positioning systems. Concerning the associated technological solutions, the new challenges to overcome are both the performance increases in terms of data quantity as well as the associated device features in terms of size, production costs, energetic consumption and reliability. In that sense, the use of higher frequency bandwidths and increase of transmission channels are aimed by various current research works. Investigated technologies are based upon integrated systems to meet the criteria of devices costs and size. As the cornerstone of such devices, the transistor largely accounts for the final system performance in terms of working frequency, reliability and consumption. To respond to the challenges of today and tomorrow challenges, alternatives to the dominant current silicon process are clearly considered. To date, gallium nitride based technology is found to be the most promising for hyperfrequency power amplification for Ka and W bands given the associated physical and electrical characteristics, prototypes performance and first commercial “off-the-shelf” products. Exploitation of this technology to its full potential requires controlling and mastering the involved fabrication, characterization and modeling steps related to the transistor. This work aims at establishing a methodology enabling a semi-physical modeling of experimental transistors which exhibit state-of-the-art performance. A significant part of this work will also focus on thermal characterization of devices under test and on modeling of secondary elements (passive elements) suited for the design of hyperfrequency amplifiers.

Cette thèse est une contribution aux développements de HEMTS AlGaN/GaN sur substrat de silicium pour des applications basses fréquences sous fortes tensions (typiquement 600V) comme les commutateurs pour la domotique ou les circuits de puissance des véhicules électriques. Elle a été menée en collaboration étroite avec Picogiga International qui a réalisé toutes les épitaxies. Elle est composée de trois parties : développement d'une technologie de fabrication, étude des courants de fuite, amélioration du pouvoir isolant de la barrière et recherche d'un comportement "normally off". La réalisation de contacts ohmiques peu résistifs est l'étape cruciale de la fabrication des HEMTs AlGaN/GaN de puissance. Une optimisation de l'empilement des métaux utilisés, de la température et du temps de recuit ainsi que la recherche d'un compromis sur la distance métallisation - gaz d'électrons, nous a permis de réaliser des contacts ohmiques proches de l'état de l'art (0,5 Ohm.mm). L'origine des courants de fuite a été systématiquement étudiée sur cinq types d'épitaxies différentes. La distance grille - drain et les courants de fuites ont été identifiés comme étant les deux facteurs limitant la tension de claquage. Selon la structure, les courants de fuite ont lieu soit à travers la grille (~e-8 A/mm à 210V), soit en parallèle au canal (e-5 A/mm). Dans les deux cas, ces courants sont comparables aux courants de fuite au travers du tampon (i.e. courants mesurés entre deux mésas). Ces courants de fuite, ont été attribués aux couches de transition nécessaires à l'adaptation de l'épitaxie des couches de nitrure sur le substrat de silicium. La réalisation de HEMT AlGaN/GaN sur silicium pour les applications à haute tension passera donc par une amélioration de ces couches tampons.Nous avons démontré qu'il est possible d'améliorer l'isolation de la barrière en AlGaN grâce à une hydrogénation du matériau. En effet un traitement de surface des transistors par un plasma hydrogène permet, par diffusion, d'y incorporer de l'hydrogène qui passive les dislocations traversantes. Après traitement, les courants de fuite de grille sont réduits et la tension de claquage est repoussée à 400V avec des courants de fuite de l'ordre de e-6 A/mm. Dans ces conditions, le claquage a alors lieu en surface de l'échantillon, il n'est plus limité que par la distance grille-drain. Ce résultat ouvre la voie à la réalisation de HEMT à forte tension de claquage (V~600V).L'effet du plasma fluoré SF6 sur les caractéristiques électriques des HEMT (AlN/GaN)/GaN (la barrière est en super-réseaux AlN/GaN) a été étudié pour la première fois dans cette thèse. Les ions fluor incorporés dans cette barrière agissent comme des donneurs qui font augmenter la densité du gaz bi-dimensionnel d'électrons et décaler la tension de pincement vers les tensions négatives. Cet effet est à l'opposé de celui observé dans les HEMT à barrière en AlGaN. Ce résultat élimine la possibilité de réaliser les HEMT (AlN/GaN)/GaN "normally off" par un dopage au fluor, une technique simple et efficace qui donne de bons résultats sur les HEMT à barrière AlGaN. D'autre part, il apporte quelques réponses expérimentales aux prévisions théoriques d'utiliser le fluor pour les dopages de type n ou p dans les nitrures d'éléments III.

Les travaux présentés dans ce mémoire d'habilitation portent sur l'impact du bruit de fond électrique sur les technologies des composants actifs, les circuits et les systèmes des hautes fréquences. Durant nos 12 dernières années de recherche, nous nous sommes notamment intéressés à des filières émergentes à fort potentiel d'intégration (BiCMOS Silicium-Germanium) ou encore à forte puissance (GaN) : nous avons ainsi développé des modèles électriques (petit signal et fort signal) et en bruit (basse fréquence et haute fréquence) des composants actifs pour identifier les pistes d'améliorations technologiques, pour localiser les défauts structurels ou pour étudier le comportement de ces mêmes défauts après l'application de contraintes simulant un vieillissement accéléré. Sur la base de la connaissance des composants actifs (transistor bipolaire à hétérojonction et transistors à effet de champ), nous avons développé des circuits intégrés MMIC faible bruit à 10 GHz et 20 GHz (amplificateurs et oscillateurs) dont certains se positionnent à l'état de l'art : des comparaisons de topologies ont notamment été réalisées sur différentes versions intégrées d'oscillateurs contrôlés en tension de type MMIC SiGe. Nous proposons également une discussion sur la pertinence des facteurs de mérite usuellement employés. D'autres études sur des atténuateurs programmables MMIC SiGe ont fait l'objet de brevets. La troisième partie, orientée système, aborde l'étude du bruit d'un récepteur : nous traitons ainsi le cas d'un étage de réception affecté par la chaîne d'émission, en proposant différentes parades permettant de limiter les dégradations de son plancher de bruit ; une technique de filtre compact intégré à l'amplificateur faible bruit a ainsi été brevetée. Enfin, le cas d'un système de liaison hertzienne embarqué sur automobile est abordé. Diverses stratégies sont ainsi proposées pour pallier les évènements conduisant à une rupture de la liaison (diversité temporelle, diversité spatiale et diversité de polarisation). Ces études reposent sur une approche mixte de traitement de mesures par des modèles théoriques, et des simulations électromagnétiques.

Innovative electronic device concepts that use polarization charges to provide improved performance were validated. The strength of the electric fields created by polarization charges (PCs) was suggested to act as an additional design parameter in the creation of devices using III-nitride and other highly polar materials. Results indicated that polarization induced electric fields can replace conventional doping schemes to create the charge separation region of solar cells and would allow for a decoupling of device performance from doping requirements. Additionally, a model for calculating current through polarization induced tunnel diodes was proposed. The model was found to agree well with experimental current values. Several polarization induced tunnel junction (PTJ) designs were analyzed. A novel double-barrier PTJ was conceived that would allow for the creation of a multi-junction solar cell using strained InGaN absorption layers. Future research would include the fabrication of these devices and the inclusion of thermal effects in the model for calculating current through PTJs.

No description available.