Le nitrure de gallium (GaN) est un matériau semi-conducteur dont la filière est en plein essor. Ses propriétés ont permis d’en faire le deuxième matériau semi-conducteur le plus utilisé pour les composants optiques et électroniques, après le silicium. Cependant, comparativement à ces domaines, peu d’études ont été menées quant à la réalisation de microsystèmes électromécaniques (MEMS) malgré des propriétés mécaniques favorables. Dans ce contexte, ces travaux présentent le développement de premiers accéléromètres MEMS résonants en filière GaN. Ces derniers reposent sur l’utilisation de poutres vibrantes possédant une forte contrainte mécanique en tension, avec un actionnement et une détection électriques intégrés. La présence de contrainte modifie significativement les performances de l’accéléromètre. Une étude théorique analytique de l’impact de la contrainte démontre ses bénéfices, notamment en termes de facteur de qualité et d’étendue de mesure. Les étapes du procédé de fabrication des composants ont été développées. Enfin, la caractérisation des accéléromètres démontre de très bonnes performances par rapport à l’état de l’art des autres filières technologiques et en accord avec les modèles préalablement établis. / The gallium nitride (GaN) is a semiconductor material for which the sector is rapidly expanding. Thanks to its properties, it have become the second most used semiconductor material for optic and electronic components, after the silicon. However, relatively to those sectors, few studies have been performed about the production of microelectromechanical systems (MEMS) despite the favorable mechanical properties. In this frame, this work presents the development of first resonant MEMS accelerometer in GaN. They are based on the use of vibrating beams which have a high tensile stress, with an integrated electrical actuation and detection. The existence of stress results in a significant modification of the performances of the accelerometer. An analytical theoretical study of the impact of the stress demonstrates its benefits, particularly for the quality factor and the measuring range. The process flow for the fabrication of the component has been developed. Finally, the characterization of the accelerometers shows very good performances compared to the state of the art of the other technologies and in agreement with the models previously established.

Le développement de composants de puissance pour les applications hyperfréquence représente un formidable défi qui doit conduire à l’amélioration des systèmes radars, spatiales ou de télécommunications existants. Les transistors de type HEMT AlGaN/GaN ont démontré leurs potentialités pour répondre à cet enjeu. Cependant, l’augmentation des performances des systèmes s’accompagne d’une miniaturisation de plus en plus poussée des transistors entrainant une augmentation de leur température de fonctionnement. Dans ce contexte, la gestion thermique des composants est très importante. Une température de fonctionnement élevée a en effet pour conséquence de dégrader les performances et la fiabilité des composants. Plusieurs voies, comme la fabrication de composants sur substrat diamant ou encore l’intégration de micro-canaux au plus près des transistors, sont en développement pour améliorer la dissipation thermique des transistors de la filière GaN. Ainsi, il a été mis en évidence que la gestion thermique des transistors est un enjeu majeur pour obtenir des systèmes performants et fiable. Afin d’optimiser la gestion thermique des composants, il est important de déterminer avec précision la température de fonctionnement des composants en temps réel. Ce travail de thèse a pour objectif le développement d’une méthode permettant de mesurer en temps réel la température de fonctionnement de transistors de type AlGaN/GaN en régime hyperfréquence. Cette mesure permettrait d’étudier la fiabilité des composants, de contrôler leur température en fonctionnement et d’assurer une maintenance préventive et non curative de systèmes. Plusieurs méthodes de la littérature permettent d’extraire la température de fonctionnement de composants. Cependant, ces méthodes ne sont pas adaptées pour mesurer la température en temps réel de composants packagés. La solution proposée ici consiste à intégrer un capteur de température résistif directement au niveau de la zone active des transistors. Un design permettant l’intégration des capteurs dans des composants compatibles pour des applications de puissance hyperfréquence au-delàs de 10 GHZ a été développé. Une partie conséquente du travail de thèse a consisté à fabriquer les dispositifs (transistors et capteurs intégrés) en central technologique. Des caractérisations thermiques des transistors fabriqués ont ensuite été menées en régime statique et hyperfréquence. / Power microwave devices development is a challenge which leads to improve radars, spatial or telecommunications systems. AlGaN/GaN HEMTs have demonstrated their capabilities to be used in such systems. However, systems performances improvement leads to miniaturize size of transistors. Consequently, the transistors operating temperature increases. As a result, thermal management is very important. A high device operating temperature will deteriorate device performances and device reliability. Several methods such as the use of diamond substrate or the integration of micro-channel lead to improve component thermal dissipation. It has been highlighted that the proper thermal management of the transistor thermal behavior is necessary to obtain performant and reliable systems. In order to improve devices thermal management, transistors’ operating temperature must be determined accurately in real time. The thesis goal consists in developing a method to measure in real time AlGaN/GaN HEMT operating temperature under microwave power condition. This method will permit to study component reliability, to control device operating temperature and to assure systems preventive maintenance purpose. According to the literature, several methods are used to determine HEMT operating temperature. However, these methods cannot be employed to determined packaged components operating temperature. To solve this problem, the proposed method in this work consists in integrating a resistive temperature sensor in the HEMT active area. A design has been developed which permits to integrate a sensor in components for microwave power applications above that 10 GHz. An important part of the thesis work consisted in fabricating the devices (transistors and sensors) in clean room. After fabrication thermal characterizations have been performed under microwave power conditions.

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Abstract In this literary, we discuss with structure and morphology improvement of GaN epilayer on c-sapphire by multi-step method in molecular-beam epitaxy. Our research is caused for the critical results of defect in GaN epilayer and rough surface morphology. In order to solve these problems we used a novel technique which we called multi-step method. In this thesis, the results of X-ray, SEM, AFM all demonstrated the achievement in our composition. However, we obtained the results of full width of half maxima (FWHM) of (0002) and (10 2) XRD rocking curves with 60~120 arcseconds and 700~ 1200 arcseconds from a series of multi-step samples respectively. Comparing with previous measurement, multi-step method is relatively superior, and the measurement of AFM roughness is under 2 nm from the series of multi-step samples. If we discuss the flat area further, we can get smoother surface which roughness is about 0.4 nm. It is obviously to recognize the flat and rough regions, but in SEM image we made sure that the flat region occupied the greater part of surface. So, in this literary we verified that the method of multi-step can improve the structure and morphology of GaN by molecular-beam epitaxy.

As the progress of the precision of optical analysis material, Raman spectra is developed as a popular optical and material analysis method. The samples of Raman spectra are low population and prepared easily and fast. Raman spectra would not destroy the samples. GaN is an ideal blue light substrate and a popular nitrogen compound of semi-conductor in III-V group . The character of the GaN is it has a wild direct band gas, high thermal conductivity and high chemical stability. This study is focus on analyzing if there is any difference of the structure of GaN growing on the different substrates. It is compared with photoluminescence spectrum to make sure the accuracy of the result of Raman spectra.

With the growth of smart phones, the demand for more broadband, data centric technologies are being driven higher. As mobile operators worldwide plan and deploy 4th generation (4G) networks such as LTE to support the relentless growth in mobile data demand, the need for strategically positioned pico-sized cellular base stations known as ‘pico-cells’ are gaining traction. In addition to having to design a transceiver in a much compact footprint, pico-cells must still face the technical challenges presented by the new 4G systems, such as reduced power consumptions and linear amplification of the signals. The RF power amplifier (PA) that amplifies the output signals of 4G pico-cell systems face challenges to minimize size, achieve high average efficiencies and broader bandwidths while maintaining linearity and operating at higher frequencies. 4G standards as LTE use non-constant envelope modulation techniques with high peak to average ratios. Power amplifiers implemented in such applications are forced to operate at a backed off region from saturation. Therefore, in order to reduce power consumption, a design of a high efficiency PA that can maintain the efficiency for a wider range of radio frequency signals is required. The primary focus of this thesis is to enhance the efficiency of a compact RF amplifier suitable for a 4G pico-cell base station. For this aim, an integrated two way Doherty amplifier design in a compact 10mm x 11.5mm monolithic microwave integrated circuit using GaN device technology is presented. Using non-linear GaN HFETs models, the design achieves high effi-ciencies of over 50% at both back-off and peak power regions without compromising on the stringent linearity requirements of 4G LTE standards. This demonstrates a 17% increase in power added efficiency at 6 dB back off from peak power compared to conventional Class AB amplifier performance. Performance optimization techniques to select between high efficiency and high linearity operation are also presented. Overall, this thesis demonstrates the feasibility of an integrated HFET Doherty amplifier for LTE band 7 which entails the frequencies from 2.62-2.69GHz. The realization of the layout and various issues related to the PA design is discussed and attempted to be solved.

¡@¡@In this thesis, the formation of m-plane (10-10) Gallium nitride (GaN) on the surface of a-plane (100) lithium gallate (LiGaO2, LGO) substrates via nitridation with ammonia (NH3) at high temperature. The parameters in this research were mainly focus on temperature, ammonia flow rate, reaction pressure, and growth time. ¡@¡@Specimens were analyzed with various instruments. X-ray Diffraction patterns showed that the nitridation process on LGO substrate resulted in the formation of the GaN single crystalline films. The crystalline quality of the GaN film could be improved by changing parameters of nitridation process. Scanning electron microscope image showed that the structure of GaN films was nanoporous. A red shift in the E2(high) phonon peak of GaN from micro-Raman indicates a compressive stress in the porous GaN with respect to the single crystalline epitaxial GaN. PL intensity ratio (INBE/IYL) of the porous GaN was found to be increased as changing parameters of nitridation process, namely the optical and crystalline quality of porous GaN was improved. Hall measurement showed that the porous GaN was p-type, and it had high hole concentration, good mobility, and low resistivity. Analyses of the elements depth profile by Auger electron spectroscopy. Transmission electron microscopy was used to observe the high resolution cross-section of porous GaN. From the selected area electron diffraction patterns, the orientation relationship between porous and LGO was determined as [100]LGO//[10-10]GaN and [0-10]LGO//[11-20]GaN when zone axis was [0001].

Electroreflectance spectra of AlGaN/GaN heteostructure were measured for various biased voltage (Vbias). There are Franz-Keldysh oscillations (FKOs) exhibiting above band gap of AlGaN, and strength of electric field of AlGaN (FAlGaN) can be evaluated from periods of the FKOs. A positive polarization charge

We have studied the electronic properties of AlxGa1-xN/GaN heterostructures by using Shubnikov¡Vde Haas(SdH) measurement. Two SdH oscillations were detected on the sample of x=0.31, due to the population of the first two subbands with the energy separations of 94.2 meV. For the samples of x=0.22 and x=0.23, two SdH oscillations beat each other, probably due to a finite zero-field spin splitting. The spin-splitting energies are equal to 1.4~5.3 and 4.5 meV . The samples also showed a persistent photoconductivity effect after illuminating by blue light-emitting diode.

The goal of this thesis is to grow InGaN at different temperatures in the form of GaN/InGaN double-heterojunction nanorods. XRD is used to analyze the In composition of film. PL, £g-PL, and CL are used to study the luminescence of InGaN and GaN, and calculation of In composition. For nanorods, the TEM and EDS are the tools to study the In composition and InGaN thickness. SEM is used to study the sample morphology. The work of EL has also been done in this thesis.