The increased power consumption and power density demands of modern technologies have increased the technical requirements of DC/DC and AC/DC power supplies. In this regard, the primary objective of the power supply researcher/engineer is to build energy efficient, high power density converters by reducing the losses and increasing the switching frequency of converters respectively. Operating the converter circuits at higher switching frequencies reduces the size of the passive components such as transformers, inductors, and capacitors, which results in a compact size, weight, and increased power density of the converter. Therefore, the thesis work is focussed on the design, analysis and evaluation of isolated converters operating in the 1 - 5MHz frequency region with the assistance of the latest semi conductor devices, both coreless and core based planar power transformers designed in Mid Sweden University and which are suitable for consumer applications of varying power levels ranging from 1 – 60W. In high frequency converter circuits, since the MOSFET gate driver plays a prominent role, different commercially available MOSFET gate drivers were evaluated in the frequency range of 1 - 5MHz in terms of gate drive power consumption, rise/fall times and electromagnetic interference (EMI) and a suitable driver was proposed. Initially, the research was focused on the design and evaluation of a quasi resonant flyback converter using a multilayered coreless PCB step down transformer in the frequency range of 2.7 – 4MHz up to the power level of 10W. The energy efficiency of this converter is found to be 72 - 84% under zero voltage switching conditions (ZVS). In order to further improve the energy efficiency of the converter in the MHz frequency region, the new material device GaN HEMT was considered. The comparisons were made on a quasi resonant flyback DC-DC converter using both the Si and GaN technology and it was found that an energy efficiency improvement of 8 – 10% was obtained with the GaN device in the frequency range of 3.2 – 5MHz. In order to minimize the gate drive power consumption, switching losses and to increase the frequency of the converter in some applications such as laptop adapters, set top box (STB) etc., a cascode flyback converter using a low voltage GaN HEMT and a high voltage Si MOSFET was designed and evaluated using a multi-layered coreless PCB transformer in the MHz frequency region. Both the simulation and experimental results have shown that, with the assistance of the cascode flyback converter, the switching speeds of the converter can be increased with the benefit of obtaining a significant improvement in the energy efficiency as compared to that for the single switch flyback converter. In order to further maximize the utilization of the transformer, to reduce the voltage stress on MOSFETs and to obtain the maximum power density from the converter circuit, double ended topologies were considered. Due to the lack of high voltage high side gate drivers in the MHz frequency region, a gate drive circuitry utilizing the multi-layered coreless PCB signal transformer was designed and evaluated in both a half-bridge and series resonant converter (SRC). It was found that the gate drive power consumption using this transformer was around 0.66W for the frequency range of 1.5 - v 3.75 MHz. In addition, by using this gate drive circuitry, the maximum energy efficiency of the SRC using multilayered coreless PCB power transformer was found to be 86.5% with an output power of 36.5W in the switching frequency range of 2 – 3MHz. In order to further enhance the energy efficiency of the converter to more than 90%, investigations were carried out by using the multiresonant converter topology (LCC and LLC), novel hybrid core high frequency planar power transformer and the GaN HEMTs. The simulated and experimental results of the designed LCC resonant converter show that it is feasible to obtain higher energy efficiency isolated DC/DC converters in the MHz frequency region. The peak energy efficiency of the LCC converter at 3.5MHz is reported to be 92% using synchronous rectification. Different modulation techniques were implemented to regulate the converter for both line and load variations using a digital controller. In order to realize an AC/DC converter suitable for a laptop adapter application, consideration was given to the low line of the universal input voltage range due to the GaN switch limitation. The energy efficiency of the regulated converter operating in the frequency range of 2.8 – 3.5MHz is reported to be more than 90% with a load power of 45W and an output voltage of 22V dc. In order to determine an efficient power processing method on the secondary side of the converter, a comparison was made between diode rectification and synchronous rectification and optimal rectification was proposed for the converters operating in the MHz frequency range for a given power transfer application. In order to maintain high energy efficiency for a wide load range and to maintain the narrow switching frequency range for the given input voltage specifications, the LLC resonant converter has been designed and evaluated for the adapter application. From the observed results, the energy efficiency of the LLC resonant converter is maintained at a high level for a wide load range as compared to that for the LCC resonant converter. Investigations were also carried out on isolated class E resonant DC-DC converter with the assistance of GaN HEMT and a high performance planar power transformer at the switching frequency of 5MHz. The simulated energy efficiency of the converter for the output power level of 16W is obtained as 88.5% which makes it feasible to utilize the designed isolated converter for various applications that require light weight and low profile converters. In conclusion, the research in this dissertation has addressed various issues related to high frequency isolated converters and has proposed solution by designing highly energy efficient converters to meet the current industrial trends by using coreless and core based planar transformer technologies along with the assistance of GaN HEMTs. With the provided solution, in the near future, it is feasible to realize low profile, high power density DC/DC and AC/DC converters operating in MHz frequency region suitable for various applications. / High Frequency Switch Mode Power Supplies

In this thesis, we address two major problems in Generative Adversarial Networks (GAN), an important sub-field in deep learning. The first problem that we address is the instability in the training process that happens in many real-world problems and the second problem that we address is the lack of a good evaluation metric for the performance of GAN algorithms. To understand and address the first problem, three approaches are developed. Namely, we introduce randomness to the training process; we investigate various normalization methods; most importantly we develop a better parameter initialization strategy to help stabilize training. In the randomness techniques part of the thesis, we developed two randomness approaches, namely the addition of gradient noise and the batch random flipping of the results from the discrimination section of a GAN. In the normalization part of the thesis, we compared the performances of the z-score transform, the min-max normalization, affine transformations and batch normalization. In the most novel and important part of this thesis, we developed techniques to initialize the GAN generator section with parameters that can produce a uniform distribution on the range of the training data. As far as we are aware, this seemingly simple idea has not yet appeared in the extant literature, and the empirical results we obtain on 2-dimensional synthetic data show marked improvement. As to better evaluation metrics, we demonstrate a simple yet effective way to evaluate the effectiveness of the generator using a novel "overlap loss".

In this thesis, we address two major problems in Generative Adversarial Networks (GAN), an important sub-field in deep learning. The first problem that we address is the instability in the training process that happens in many real-world problems and the second problem that we address is the lack of a good evaluation metric for the performance of GAN algorithms. To understand and address the first problem, three approaches are developed. Namely, we introduce randomness to the training process; we investigate various normalization methods; most importantly we develop a better parameter initialization strategy to help stabilize training. In the randomness techniques part of the thesis, we developed two randomness approaches, namely the addition of gradient noise and the batch random flipping of the results from the discrimination section of a GAN. In the normalization part of the thesis, we compared the performances of the z-score transform, the min-max normalization, affine transformations and batch normalization. In the most novel and important part of this thesis, we developed techniques to initialize the GAN generator section with parameters that can produce a uniform distribution on the range of the training data. As far as we are aware, this seemingly simple idea has not yet appeared in the extant literature, and the empirical results we obtain on 2-dimensional synthetic data show marked improvement. As to better evaluation metrics, we demonstrate a simple yet effective way to evaluate the effectiveness of the generator using a novel "overlap loss".

GaN is a monocrystalline material that can be grown using metallo-organic chemical vapour deposition (MOCVD), and has desirable mechanical and semiconducting properties for operating as a sensor. It has a Young’s modulus of 250 to 350 GPa, which shows little decrease with respect to temperature beyond 400°C. GaN also exhibits piezoelectric and piezoresistive effects, meaning that it will generate a charge and its electrical resistance will change when the material is strained respectively. In this PhD, GaN has been used as the base material for pressure sensors that potentially can be used in excess of 400°C and at a pressure in excess of 50 bar (5 MPa), with potential applications in aerospace and oil exploration. The pressure sensor is a circular diaphragm created from a GaN/sapphire wafer, and was designed and tested in order to determine if GaN can act as a sensing material in these environments. In addition to the diaphragm sensor, GaN templates that can potentially be used for sensors were grown using an epitaxial layer overgrowth (ELOG) method. These sensors are potentially more mechanically robust than similar templates etched out of GaN/sapphire wafers because they will have less inbuilt strain due to lower dislocation densities. It was possible to release beams and cantilevers from GaN ELOG templates. Mechanical probe tests were undertaken on these devices to see if they were fully released and robust. GaN single crystal growth requires a substrate material, such as (111) silicon or (0001) sapphire, meaning that the thermal properties of the substrate are important for a device operating in excess of 400°C. GaN high electron mobility transistors are heat sensitive, experiencing a decrease in current between the drain and source terminals as the temperature increases. Therefore a GaN-based sensor needs a substrate with the highest possible thermal conductivity to act as a heat sink, which means removing as much heat as possible from the GaN sensor. Diamond has superior thermal conductivity to both sapphire and silicon, so a novel silicon/polycrystalline diamond composite substrate has been developed as a potential GaN substrate. Polycrystalline diamond (PD) can be grown on 4 inch diameter wafers using hot filament chemical vapour deposition (CVD), on (111) silicon (Si) from which single crystal GaN epitaxy can also be grown. In order for the (111) Si/PD composite substrates to be useful heat sinks, the Si layer needs to be less than 2 m. PD was initially grown on 525 to 625 m thick Si wafers that required thinning to 2 m. Achieving this Si layer thickness is difficult due to the presence of tensile stress in the Si caused by a mismatch in the coefficients of thermal expansion (CTEs) between Si and PD. This stress causes the wafer to bow significantly and has been modelled using ANSYS FE software. The models show that the bow of the wafer increases when it is thinned, which will eventually cause the Si layer to delaminate at the Si/PD interface due to poor adhesion and a build up for shear stress. When the Si layer is mechanically thinned, the Si layer can crack due to clamping. The experimental wafer bow and micro-Raman measurements validate the model for when the silicon layer is thicker than 100 m and these results show that an alternative processing route is required.

La spintronique utilisant des matériaux semi-conducteurs est un sujet de recherche très actif. Elle permet de combiner le potentiel des semi-conducteurs avec le potentiel des matériaux magnétiques. Le GaN pourrait être un bon candidat pour des applications en spintronique car le temps de relaxation de spin est très long. La spintronique organique est également un domaine de recherche en plein essor en raison de la longue durée de vie de spin des porteurs de charge ainsi que de leur coût relativement bas, de leur flexibilité et de leur diversité chimique. Dans un premier temps, nous montrerons que la polarisation circulaire de la lumière émise par une LED contenant une couche unique de points quantiques InAs / GaAs (QD) InAs / GaAs dopés p peut atteindre environ 18% sans champ magnétique extérieur. Une corrélation claire est établie entre le degré de polarisation de la lumière émise et l’aimantation perpendiculaire de l’injecteur. La polarisation atteint un maximum pour une polarisation appliquée de 2.5 V à 10 K, ce qui correspond à un courant injecté de 6 µA. En outre, nous observons un comportement remarquable de la polarisation pour un température comprise entre 60K et 80K. L’évolution de la polarisation en fonction de la température est discutée à la lumière de la compétition entre le temps de vie de recombinaison radiative τr et le temps de relaxation de spin τs. De plus, nous avons développé un injecteur de spin présentant une anisotropie magnétique perpendiculaire sur GaN. Nous avons d’abord optimisé la croissance de MgO pour différentes températures du substrat. Nous avons ensuite étudié la croissance de Fe puis de Co sur MgO/GaN. L’injecteur de spin Co(0001)/MgO(111) a été retenu car celui-ci permet d’obtenir un anisotropie magnétique perpendiculaire. De plus, les calculs ab initio ont également montré que l’interface Co/MgO(111) présente une grande anisotropie magnétique. Finalement, nous étudions les MFTJ basés sur une barrière de PVDF organique dopée avec des nano-particules de Fe3O4. Nous avons fabriqué avec succès une multicouche de La0.6Sr0.4MnO3/PVDF:Fe3O4/Co, dans laquelle la barrière organique en poly (fluorure de vinylidène) (PVDF) a été dopée avec des nanoparticules ferromagnétiques de Fe3O4. En modifiant la polarisation du PVDF, l’effet tunnel dans la jonction multiferroïque peut être commuté via la partie LSMO/PVDF/Co (polarisation positive) ou via la partie Fe3O4/PVDF/Co (polarisation négative). Cela correspond à une inversion de la magnétorésistance à effet tunnel (TMR) de + 10% à -50%, respectivement. Notre étude montre que les jonctions tunnel multiferroïques organiques dopées avec des particules magnétiques pourraient créer de nouvelles fonctionnalités en jouant sur l’interaction du magnétisme des nanoparticules avec la ferroélectricité de la barrière organique. / Spintronics with semiconductors is very attractive as it can combine the potential of semiconductors with the potential of the magnetic materials. GaN has a long spin relaxation time, which could be of potential interest for spintronics applications. Organic spintronics is also very appealing because of the long spin lifetime of charge carriers in addition to their relatively low cost, flexibility, and chemical diversity. In this thesis, we investigate spin injection in spin LEDs containing either InAs/GaAs quantum dots or InGaN/GaN quantum wells. Moreover, we further study spin polarized transport in organic multiferroic tunnel junctions (OMFTJs). Firstly, we will show that the circular polarization of the light emitted by a LED containing a single layer of p-doped InAs/GaAs quantum dots (QDs) can reach about 18% under zero applied magnetic field. A clear correlation is established between the polarization degree of the emitted light and the perpendicular magnetization of the injector layer. The polarization reaches a maximum for an applied bias of 2.5V at 10K, which corresponds to an injected current of 6 µA. Also, we report a remarkable behavior of the polarization in the temperature region 60-80K. The interpretation of the bias and temperature dependence of the polarization is discussed in light of the competition between radiative recombination time τr and the spin relaxation time τs. In addition, significant efforts have been devoted to developing a perpendicular spin injector on GaN based materials to achieve spin injection without applying a magnetic field. Firstly, the growth of MgO has been investigated at various growth temperatures. Then, we studied the growth of either Fe or Co on MgO/GaN. In contrast to Fe/MgO, the Co/MgO spin injector yields a clear perpendicular magnetic anisotropy. In addition, ab-initio calculations have been performed to understand the origin of the perpendicular magnetic anisotropy at the Co/MgO(111) interface. Finally, we investigate multiferroic tunnel junctions (MFTJs) based on organic PVDF barriers doped with Fe3O4 nano particles. The organic MFTJs have recently attracted much attention since they can combine advantages of spintronics, organic and ferroelectric electronics. We report on the successful fabrication of La0.6Sr0.4MnO3/PVDF:Fe3O4/Co OMFTJ, where the poly(vinylidene fluoride) (PVDF) organic barrier has been doped with ferromagnetic Fe3O4 nanoparticles. By changing the polarization of the ferroelectric PVDF, the tunneling process in OMFTJ can be switched either through the LSMO/PVDF/Co part (positive polarization) or through the Fe3O4/PVDF/Co part (negative polarization). This corresponds to a reversal of tunneling magnetoresistance (TMR) from +10% to -50%, respectively. Our study shows that the doping of OMFTJs with magnetic nanoparticles can create new functionalities of organic spintronic devices by the interplay of nanoparticle magnetism with the ferroelectricity of the organic barrier.

L’amplificateur haute puissance d’un radar, qui est l’un des éléments définissant les performances du système, est un sujet constant de rechecherche afin d’améliorer sa puissance et son rendement. Des améliorations des performances peuvent être apportées par la combinaison d’une technologie relativement nouvelle, le HEMT GaN et de classes de fonctionnement d’amplificateur à haut rendement telles les classes de commutation. Ces dernières faisant usage des harmoniques du signal complexe émis par l’amplificateur en compression, une caracterisation non linéaire est requise. Ce type de caractérisation existe déjà en mode CW et pulsé périodique. Cependant, le mode pulsé périodique n’apporte qu’une approximation du train d’impulsions radar réel excitant l’amplificateur, négligeant les effets causés par le train de pulse. Cela concerne particulièrement la technologie HEMT GaN qui est susceptible à des effets thermique et de mémoire. Ce travail propose une nouvelle technique de mesure reposant sur un prototype de NVNA basé sur des mélangeurs capable de mesurer trois fréquences simultanément, permettant la caractérisation non linéaire d’un amplificateur en condition radar réelle en terme de train d’impulsions. Cet instrument a été validé par des mesures CW et pulsée périodique en utilisant un appareil type LSNA et un VNA disponible sur le marché. La technique mesure, optimisée dans ce travail jusqu’à 12GHz, permet de visualiser des effets causés par le train d’impulsions sur l’amplificateur de puissance tout en mesurant les trois premiers tons du signal complexe au meilleur rapport signal à bruit disponible grâce à l’architecture de l’instrument. / Radar high power amplifier, that is one of the performance defining elements of a radar system, is under constant investigation to improve its power and efficiency. Improvement can be provided through the combination of relatively new transistor technology such as HEMT GaN and the use of high efficiency functioning class such as commutation classes. Commutation classes making use of harmonic tones of the complex signal of the amplifier at compression, non- linear characterization is required. Such characterization already available for CW and periodic pulse signal. However periodic pulse only provide an approximation of the actual radar pulse train the amplifier will be submitted to, overlooking effects cause by the pulse train. This affect especially on HEMT GaN which is prone to thermal and memory effects. This work propose a new measurement technique relying on a developed mixer based NVNA prototype able to measure three frequencies simultaneously, allowing the non linear characterization of a power amplifier in actual non periodic radar pulse train. The instrument was validated in CW and periodic pulse condition using commercially available NVNA and a LSNA. The measurement technique, optimized in this work to be performed up to 12GHz, allowed to see effects caused by the radar pulse train on a power amplifier performance while recording all three tones at best signal to noise ratio available thanks to the instrument architecture.

L'objectif de cette thèse est la réalisation d'une source de puissance pulsée à transistors GaN. Après une étude d'applications des micro-ondes de forte puissance, ainsi qu'un état de l'art des sources, nous avons réalisé deux prototypes de modules élémentaires d'amplification (bande large et bande étroite). Le module bande large délivre 70 W CW de 1 à 2,5 GHz et le module bande étroite délivre une puissance supérieure à 550 W de 1,1 à 1,3 GHz, avec un pic de 750 W à 1,1 GHz, dans des impulsions de 500 µs avec un rapport cyclique de 10 %. Une difficulté est que les transistors GaN ont des impédance d'entrée et de sortie faibles, entre 1 et 5 Ω, difficile à adapter vers le standard 50 Ω sur une large bande, et qu'il faut combiner les puissances de plusieurs transistors entre eux pour atteindre des puissances élevées, tout en assurant leur isolation mutuelle pour éviter la propagation de pannes et des oscillations. Nous avons développé un combineur de puissance utilisant une préadaptation d'impédance avec un plan de masse fendu permettant d'avoir une impédance d'entréee basse, 2,5 Ω, et utilisant un absorbant micro-ondes afin d'éviter de réfléchir les modes impairs, ce qui permet d'isoler les transistors entre eux. / The goal of this thesis is to realize a pulsed power source with GaN transistors. After a study of the applications of high power microwaves, and a state of the art of the sources, we realized two prototypes of elementary amplifier modules (wide and narrow band). The wideband module produces 70 W CW from 1 to 2.5 GHz, and the narrowband module produces a power higher than 550 W from 1.1 to 1.3 GHz, with a 750 W peak at 1.1 GHz, in 500 µs pulses with 10 % duty cycle. One difficulty is that GaN transistors have low input and output impedances, from 1 to 5 Ω, difficult to adapt towards the 50 Ω standard on a wide bandwidth, and that several transistors need to be combined to reach high input powers, ensuring their mutual isolation to avoid failure propagation and oscillations. We developpes a power combiner using an impedance pre-adaptation with a deffective ground plane allowing to reach a 2.5 Ω low input impedance, and using a microwave absorber to avoid odd mode reflections, which allows the mutual isolation of the transistors.

Depuis quelques années, nous assistons à l’essor d’une nouvelle filière d’électronique basée sur des supports flexibles. De nombreuses applications difficilement atteignables par l’électronique classique sont visées, c’est notamment le cas des tags RFID, des capteurs mobiles, des écrans flexibles…. Cette électronique est essentiellement basée sur des matériaux organiques pour lesquels la faible mobilité (<1cm2 /V.s) limite considérablement les performances hyperfréquences des composants. Dans ce contexte, l’intégration hétérogène de composants des filières GaN et graphène sur substrat flexible apparait comme une solution prometteuse pour des applications de puissance hyperfréquence où la conformabilité sur surface non plane est souhaitée. Ces travaux présentent d’une part, une méthode de transfert de composants HEMTs AlGaN/GaN sur ruban flexible et d’autre part, une technique de manipulation du substrat souple et de fabrication directe des composants à base de graphène sur celui-ci. Des HEMTs AlGaN/GaN à faible longueur de grille (LG = 100nm) ont été transférés sur ruban flexible et ont permis d’atteindre des résultats à l’état de l’art en termes de puissance hyperfréquence avec un gain de puissance linéaire (Gp) de 15,8 dB, une densité de puissance de sortie (Pout) de 420 mW / mm et une puissance ajoutée (PAE) de 29,6%. Pour les composants à base de graphène, une technique de manipulation du substrat flexible a été développée et a permis de fiabiliser le procédé technologique de fabrication. Une fréquence de coupure ft de 1GHz et une fréquence maximale d’oscillation fmax de 3 GHz ont été obtenues. / In recent years, the field of flexible electronics has been expanding. Many applications difficult to achieve by conventional electronics are targeted as RFID tags, mobile sensors, flexible screens… This field is essentially based on organic material for which the poor mobility (<1cm2 /V.s) limits considerably the device performances. In this context, the heterogeneous integration of GaN and graphene devices on a flexible substrate appears to be a promising solution for microwave power applications where conformability on a non-planar surface is needed. This work presents, on the one hand, a method to transfer AlGaN/GaN HEMTs onto flexible tape and, on the other hand, a technique for handling and manufacturing graphene-based components directly on the flexible substrate. HEMTs with short-gate length (LG = 100 nm) have been transferred onto flexible tape and showed state of the art results in terms of microwave power with a linear power gain (Gp) of 15.8 dB, an output power density (Pout) of 420 mW/ mm and an added power efficiency (PAE) of 29.6%. Concerning graphene-based devices, a flexible substrate handling technique has been developed making the manufacturing process more reliable. A cut-off frequency ft of 1 GHz and a maximum oscillation frequency fmax of 3 GHz were obtained.

Ce travail est porté sur les propriétés structurales et optiques de structures à boîtes quantiques III-nitrures dopées avec des terres rares réalisées par épitaxie à jets moléculaires.<br />Pendant la croissance, les terres rares ont une influence drastique sur les boîtes, expliquée par les propriétés surfactantes des atomes de terres rares.<br />La caractérisation optique et structurale montre que les boîtes sont dopées efficacement avec les ions de Eu, Tm et Tb. D'autres localisations des terres rares ont été trouvées, par exemple, pour le Tm, à l'interface du GaN des boîtes et de l'AlN.<br />Ce travail s'intéresse aussi à la dynamique d'excitation de boîtes quantiques dopées aux terres rares. La photoluminescence de couleurs intéressantes est stable de la température de l'hélium liquide jusque la température ambiante.<br />Des structures à boîtes quantiques plus complexes sont aussi abordées : des boîtes InGaN:Eu QDs et des boîtes GaN co-dopées, importante pour la réalisation de composants.<br />Une attention particulière a été mise sur les couches de GaN dopé Eu, où différents sites pour l'Eu ont été mis en évidence près de surface et à l'intérieur de matériau.

Une méthode originale de croissance non catalysée a été développée pour faire croître des fils auto-assemblés de GaN sur des substrats de saphir par épitaxie en phase gazeuse d'organo-métalliques (MOVPE). Cette approche, basée sur le dépôt et le perçage, in situ, d'une fine couche de SiNx (~2 nm), permet la croissance épitaxiale de fils orientés le long de l'axe c sur des substrats de saphir. L'étude détaillée des mécanismes de croissances montre qu'une combinaison de paramètres clés est nécessaire pour obtenir la croissance verticale des fils. En particulier, la durée du dépôt de SiNx avant la croissance des fils est critique pour contrôler l'épitaxie avec le substrat. Le temps de nucléation des germes de GaN détermine la taille moyenne et la qualité structurale, enfin une forte concentration de dopant Si permet d'obtenir la croissance verticale. Les fils obtenus ont une émission UV centrée sur environ 350 nm et une faible bande jaune de défaut (~550 nm) à basse température. Cette approche fournit une méthode rapide et reproductible pour faire croître des fils de GaN en MOVPE et a permis d'explorer les paramètres de croissance sans avoir à préparer spécifiquement les surfaces comme c'est le cas dans les croissances sélectives. La croissance d'hétérostructures dopées longitudinales de type n-u et n-p a été démontrée en utilisant des précurseurs de Si et de Mg. De plus les fils ont été utilisés comme gabarits pour faire croître des structures cœur/coquille de puits quantiques InGaN/GaN. Ces structures ont été étudiées par cathodo- et photo-luminescence pour avoir une caractérisation spatiale et spectrale de l'émission lumineuse. Cette croissance se fait notamment sur les plans m non-polaires ce qui modifie les contributions des champs électriques sur l'émission de lumière. Les briques technologiques pour obtenir une diode électroluminescente bleue à base de fils ont donc été démontrées. La réalisation de composants nécessite un contrôle plus poussé de la qualité du matériau et des contacts pour une injection électrique.