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Wide bandgap semiconductors have entered into Naval radar use and will eventually replace vacuum tube and conventional solid-state amplifiers for all modern military radar and communications applications. Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) are on the leading edge of wide bandgap technology and have the performance characteristics to dominate in high power â high bandwidth applications. The Defense Advanced Research Projects Agency (DARPA), Office of Naval Research (ONR) and Missile Defense Agency (MDA) are all sponsoring research projects to apply wide bandgap technology. This thesis studies the effects of changing the substrate material of an existing GaN HEMT from sapphire to diamond through the use of commercially available Silvaco software for modeling and simulation. The unparalleled thermal properties of diamond are expected to dramatically decrease device temperatures and increase component lifetimes and reliability.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Afin de développer des méthodes alternatives à l'activation de systèmes Pi en catalyse homogène par des métaux nobles coûteux et toxiques, nous nous sommes focalisés sur des complexes métalliques et plus particulièrement ceux de la colonne du group XIII. Cette thèse approche une contribution à ce champ d'études, et nous nous sommes particulièrement concentrés sur la chimie de gallium.Trois principaux aspects ont été étudiés dans ce manuscrit: la réactivité des halogénures de gallium(III), des complexes bien définis de gallium (III) portant carbènes N- hétérocycliques (NHCs), et leur activation de systèmes en catalyse.La thèse est divisée en trois chapitres. Le premier chapitre donne un aperçu des travaux effectués dans le domaine de la synthèse organique faisant intervenir des composés de gallium (III) , en se concentrant sur ​​leur utilisation en tant qu’ acides de Lewis et .Dans le deuxième chapitre, nous avons tenté d'exploiter le potentiel catalytique de GaCl3 dans une nouvelle réaction de cycloisomérisation/Friedel-Crafts en tandem. Une section dédiée à l'étude sur l’hydratation d’alcyne catalysée par GaCl3 est également fournie.Le troisième chapitre commence par une description de la synthèse d'une série de complexes de gallium (III) portant diverses NHCs comme ligands pour surmonter les limites des halogénures de gallium(III) en catalyse. Ensuite, des études de méthodologie sur le processus de tandem impliquant arenynes-1,6 avec les gallium(III) complexes neutres et cationiques ont été décrits. Une évaluation cinétique pour des catalyseurs, des divers substrats et l'influence de contreanions sont discutés. En outre, les efforts dans la version asymétrique de cette tandem transformation et des autres cyclisations sont également présentés.Le dernier chapitre reprend les résultats les plus importants obtenus dans la thèse. Et les orientations futures de la recherche sur l'utilisation des complexes NHC- gallium (III) sont discutées. / Recently, in order to develop alternative activation methods for Pi-systems in homogeneous catalysis instead of employing expensive and toxic noble metal catalysts, first row transition metals and main group metal complexes have attracted great attention. This thesis is a contribution to it, and we focus on gallium chemistry. There are three main aspects dominating this thesis: gallium(III) halides, well-defined gallium(III) complexes bearing N-heterocyclic carbenes (NHCs), and -systems activation in catalysis.The thesis is divided into three chapters. Chapter I provides an overview of the field of organic synthesis involving gallium(III) compounds, focusing on their use as - or -Lewis acids.In Chapter II, we expose our attempts to exploit the catalytic potential of gallium(III) chloride in a novel tandem cycloisomerization/Friedel-Crafts reaction. A section dedicated to the study on GaCl3-catalyzed alkyne hydration is also provided.Chapter III begins with a description of the synthesis of a series of gallium(III) complexes bearing various NHCs as ligands in order to overcome the limitations of gallium(III) halides in catalysis. Next, methodology studies on the tandem process involving 1,6-arenynes with the neutral and cationic gallium(III) complexes are described. The evaluation of scission kinetics for catalysts, substrates variation and influence of counteranions are discussed. In addition, efforts towards the asymmetric version of this tandem transformation and some other cyclizations are also presented.The concluding chapter reiterates the most important results obtained in the body chapters of the thesis. To conclude, the future directions for the research on the use of the NHC-gallium(III) complexes are discussed.

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

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

Graduation date: 1992

Graduation date: 1992

This research is related to the molecular beam epitaxy (MBE ) to grow GaSb . The fabrication of GaSb/InGaSb strained quantum well and superlattice structures are used for photodetection . They are carefully investigated to obtain high quality of GaSb films. The growth mechanisms related to the major factors of (1) Subtrate temperature (2) Beam flux ratio(V/III). The properties of GaSb epilayers are characterized by different methods such as the X-ray diffraction , I-V curve and Raman spectra . The optimum growth conditions 500¢J of substrate temperature and the V/III flux ratio about 2~3 have been obtained. On the basis of structure, the best growth conditions is identified by the peak intensity and FWHM related to the quality of the GaSb films by the X-ray diffraction. On the basis of electrical property, the best growth conditions is identified by the lowest leakage current for the p-n junction related to the quality of the GaSb films by the I-V curve. On the basis of optical property, the best growth conditions is identified by the LO mode phonon intensity related to the quality of the GaSb films by the Raman spectra. Based on the GaSb growth studied here, the study will be focused in the quantum well and quantum dot laser devices furtherly by us.

Thesis (Ph. D.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xvii, 161 p. : ill. Includes abstract. Includes bibliographical references (p. 154-161).