Ces dernières années, le nombre de circuits intégrés micro-ondes utilisés dans les systèmes de télécommunications a fortement augmenté suite à l'utilisation de fréquences porteuses de plus en plus élevées. Ce type de circuits intégrés est très fréquemment utilisé dans les équipements pour la téléphonie mobile et pour les communications satellitaires. Le développement, la mise au point et l'optimisation des circuits intégrés nécessitent l'usage d'outils de mesure et de simulation performants. Ces outils permettent par exemple de localiser les points critiques de la conception. Considérant le nombre limité d'entrées et de sorties d'un circuit intégré, l'information sur les signaux électriques à l'intérieur même du circuit intégré est difficilement accessible. Plusieurs techniques de mesure permettant d'accéder à une mesure des champs électromagnétiques à l'intérieur des circuits ont donc été proposées ou sont en développement. Cette thèse est centrée sur le sondage des circuits micro-onde monolithiques intégrés (MMIC) à base d'Arséniure de Gallium. L'idée sous-jacente est d'exploiter les propriétés électro-optiques du substrat semi-conducteur. Un faisceau laser est focalisé sur le circuit à tester. Considérant que l'Arséniure de Gallium est "transparent" pour la longueur d'onde choisie, le faisceau entre dans le composant et il se réfléchit sur la face arrière. Le faisceau réfléchi est modulé par le signal micro-onde en vertu de l'effet Pockels qui impose une modification de l'indice de réfraction optique du matériau sous l'effet d'un champ électrique. Cette modulation, qui peut être mesurée, permet de déduire l'intensité du champ électrique le long du parcours de l'onde optique dans le circuit intégré. L'objectif de cette thèse est la construction d'un prototype à partir de travaux préliminaires réalisés dans le laboratoire du groupe de télécommunications optiques de Télécom Paris. Le but recherché est une conception simple, permettant une utilisation aisée de l'outil à des coûts de matériel réduits. Par conséquent, les composants utilisés sont tous des composants standards du commerce. La réalisation majeure de ce travail correspond à la mise au point d'un instrument entièrement automatisé amenant des mesures très fiables grâce l'utilisation d'équipements nouveaux nettement plus performants. En particulier avec l'utilisation de fibres à maintien de polarisation, toutes les manipulations du faisceau laser en espace libre sont évitées. Les logiciels d'acquisition de donnée ont été intégralement renouvelés et adaptés au produit. Un certain nombre de problèmes théoriques négligés dans les travaux précédents sont de plus réglés comme par exemple celui concernant la validité des résultats de sondage si la direction du champ électrique n'est pas connue exactement. Le problème de l'adéquation de la focalisation du faisceau laser sur le circuit intégré et de la résolution spatiale qui en découle a été analysé. Dans cette thèse, nous décrivons le développement de l'outil et les résultats correspondants. Nous démontrons que les résultats mesurés correspondent à la description théorique. Une sensibilité d'environ 2[mV/

<p><p>In this work growth of cubic GaN in the selective area (SA) MOVPE process is</p><p>simulated. The simulations are restricted to small pattern SA MOVPE growth.</p><p>In this case the traditional MOVPE growth and the enhanced growth caused by</p><p>surface diffusion are important growth factors. The lateral vapor phase diffusion</p><p>is ignored while this process only has a small impact on the enhanced growth in</p><p>the small pattern SA growth. The model is build for simulation of anisotropic</p><p>growth. It has been shown that different type of anisotropic growth occurs when</p><p>the mask pattern are orientated in different directions on the substrate. While</p><p>the anisotropic growth is not well understood two different models are studied in</p><p>this work.</p><p>The simulation is restricted to the geometrical growth characteristics such</p><p>as mask and crystal width, mask alignment and surface diffusion on the crystal.</p><p>The reactor geometry, pressure and growth temperature are not investigated that</p><p>closely and are only treated as constants in the model.</p><p>The model used in this simulation gives good results for short time simulations</p><p>for some certain cases. The model shows that the fill factor has a greater</p><p>impact on the grown shapes than the individual mask and crystal width. But</p><p>there are problems with the anisotropic and flux from mask modeling while some</p><p>facets do not appear and the lateral growth along the mask show doubtful results.</p><p>The model show good results in short time growth and predict some important</p><p>characteristics in SA MOVPE.</p></p>

Graduation date: 1996

Uniformly distributed ZnO nanorods with diameter 70-100 nm and 1-2μm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip (needle shape) to flat tip (rod shape). These kinds of structure are useful in laser and field emission application. / Singapore-MIT Alliance (SMA)

High density, uniform GaN nanodot arrays with controllable size have been synthesized by using template-assisted selective growth. The GaN nanodots with average diameter 40nm, 80nm and 120nm were selectively grown by metalorganic chemical vapor deposition (MOCVD) on a nano-patterned SiO2/GaN template. The nanoporous SiO2 on GaN surface was created by inductively coupled plasma etching (ICP) using anodic aluminum oxide (AAO) template as a mask. This selective regrowth results in highly crystalline GaN nanodots confirmed by high resolution transmission electron microscopy. The narrow size distribution and uniform spatial position of the nanoscale dots offer potential advantages over self-assembled dots grown by the Stranski–Krastanow mode. / Singapore-MIT Alliance (SMA)

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

In this work growth of cubic GaN in the selective area (SA) MOVPE process is simulated. The simulations are restricted to small pattern SA MOVPE growth. In this case the traditional MOVPE growth and the enhanced growth caused by surface diffusion are important growth factors. The lateral vapor phase diffusion is ignored while this process only has a small impact on the enhanced growth in the small pattern SA growth. The model is build for simulation of anisotropic growth. It has been shown that different type of anisotropic growth occurs when the mask pattern are orientated in different directions on the substrate. While the anisotropic growth is not well understood two different models are studied in this work. The simulation is restricted to the geometrical growth characteristics such as mask and crystal width, mask alignment and surface diffusion on the crystal. The reactor geometry, pressure and growth temperature are not investigated that closely and are only treated as constants in the model. The model used in this simulation gives good results for short time simulations for some certain cases. The model shows that the fill factor has a greater impact on the grown shapes than the individual mask and crystal width. But there are problems with the anisotropic and flux from mask modeling while some facets do not appear and the lateral growth along the mask show doubtful results. The model show good results in short time growth and predict some important characteristics in SA MOVPE.

<p>Graphene is a novel carbon material with great promise for a range of applications due to its electronic and mechanical properties. Its two-dimensional nature translates to a high sensitivity to surface chemical interactions thereby making it an ideal platform for sensors. Graphene's electronic properties are not degraded due to mechanical flexing or strain (Kim, K. S., et al. nature 07719, 2009) offering another advantage for flexible sensors integrated into numerous systems including fabrics, etc. </p><p>We have demonstrated a graphene NO2 sensor on a solid substrate (100nm SiO2/heavily doped silicon). Three different methods were used to synthesize graphene and the sensor fabrication process was optimized accordingly. Water is used as a controllable p-type dopant in graphene to study the relationship between doping and graphene's response to NO2. Experimental results show that interface water between graphene and the supporting SiO2 substrate induces higher p-doping in graphene, leading to a higher sensitivity to NO2, consistent with theoretical predications (Zhang, Y. et al., Nanotechnology 20(2009) 185504). </p><p>We have also demonstrated a flexible and stretchable graphene-based sensor. Few layer graphene, grown on a Ni substrate, is etched and transferred to a highly stretchable polymer substrate (VHB from 3M) with preloaded stress, followed by metal contact formation to construct a flexible, stretchable sensor. With up to 500% deformation caused by compressive stress, graphene still shows stable electrical response to NO2. Our results suggest that higher compressive stress results in smaller sheet resistance and higher sensitivity to NO2. </p><p>A possible molecular detection sensor utilizing Surface Enhanced Raman Spectrum (SERS) based on a graphene/gallium nanoparticles platform is also studied. By correlating the enhancement of the graphene Raman modes with metal coverage, we propose that the Ga transfers electrons to the graphene creating local regions of enhanced electron concentration modifying the Raman scattering in graphene.</p> / Dissertation

This thesis reports on the growth and characterization of p-type pseudomorphic A1GaAs /InGaAs /GaAs modulation doped field effect transistor (MODFET) structures. A series of different p-type MODFET structures were grown with a systematic variation of the indium mole fraction and quantum well width of the InGaAs channel region. Extensive characterization of these samples using van der Pauw Hall and photoluminescence measurements showed clear trends in carrier mobility and quantum well quality with respect to the structure of the InGaAs region. From this an optimal indium mole fraction and quantum well width were obtained. Subsequent to material characterization, MODFET devices were fabricated and characterized. The measured DC device performance was reasonable and suggests that high quality p-type MODFETS should be obtainable with a properly optimized device structure and fabrication process. / Graduation date: 1993

The semiconductor gallium arsenide (GaAs) has many potential advantages over the more widely used semiconductor silicon (Si). These include higher low field mobility, semi-insulating substrates, a direct band-gap, and greater radiation hardness. All these advantages offer distinct opportunities for implementation of new circuit functions or extension of the operating conditions of similar circuits in silicon based technology. However, full exploitation of these advantages has not been realized. This study examines the limitations imposed on conventional GaAs metal-semiconductor field effect transistor (MESFET) technology by deviations of the semi-insulating substrate material from ideal behavior. The interaction of the active device with defects in the semi-insulating GaAs substrate is examined and the resulting deviations in MESFET performance from ideal behavior are analyzed. A p-well MESFET technology is successfully implemented which acts to shield the active device from defects in the substrate. Improvements in the operating characteristics include elimination of drain current transients with long time constants, elimination of the frequency dependence of g[subscript ds] at low frequencies, and the elimination of sidegating. These results demonstrate that control of the channel to substrate junction results in a dramatic improvement in the functionality of the GaAs MESFET. The p-well MESFET RF characteristics are examined for different p-well doping levels. Performance comparable with the conventional GaAs MESFET technology is demonstrated. Results indicate that optimization of the p-well MESFET doping levels will result in devices with uniform characteristics from DC to the highest operating frequency. / Graduation date: 1991