Thesis (Ph. D.)--University of Missouri-Columbia, 1996. / Typescript. Vita. Includes bibliographical references (leaves 97-102). Also available on the Internet.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Nov. 20, 2008). PDF text: xvii, 187 p. : ill. (some col.) ; 11 Mb. UMI publication number: AAT 3311304. Includes bibliographical references. Also available in microfilm and microfiche formats.

Cette thèse porte sur la fabrication de diodes Schottky sur diamant pour des applications hautes puissances. La croissance du diamant et son dopage sont aujourd'hui bien maîtrisés. La passivation de la surface du diamant (surface à terminaison oxygène) requise pour minimiser les états d'interface et obtenir des contacts redresseurs sur diamant, est également bien maîtrisé. L'apparition des architectures verticales (couche active des diodes épitaxiée sur un substrat de diamant fortement dopée) et pseudo-vertical (épitaxie d'un empilement comprenant la couche active et une couche fortement dopée sur un substrat diamant isolant) ont permis de minimiser la résistance série élevée des diodes sur diamant (énergie d'ionisation élevée des principaux dopants du diamant). Malgré le fait que ces configurations géométriques favorisent courants directs élevés, les performances diodes Schottky verticales ou pseudo verticales sur diamant sont à ce jour limitées par: i) la qualité de la couche active altérée par la propagation de défauts issues de la couche fortement dopée conduisant à de faible champ critiques (environ 3 MV / cm au lieu des 10MV/cm théorique), ii) les contacts Schottky sélectionnés, la stabilité thermique et chimique des interfaces formées avec une surface de diamant à terminaison oxygène. La sélection du métal Schottky et le prétraitement de la surface sont cruciaux pour obtenir de faibles hauteurs barrières (faible chute de tension à l'état passant), une faible densité de défauts au niveau des interfaces (faible courants de fuite), et une interface thermiquement stable (température de fonctionnement élevée). Dans cette thèse, nous avons démontré qu'une diode Schottky diamant pseudo verticale basée sur l'utilisation d'une surface à terminaison oxygène couverte par un métal facilement oxydable comme le zirconium (Zr), et une couche fortement dopée avec une épaisseur optimale, permettent de surmonter ces limitations et de fabriquer des diodes de meilleurs performances que l'état de l'art actuel. Un compromis entre l'épaisseur de la couche fortement dopée et son niveau de dopage à été d'abord établit afin de minimiser la génération de défauts et par conséquent d'améliorer la qualité de la couche active. Le métal (Zr) sélectionné comme contact Schottky donnait lieu à la formation d'une fine couche d'oxyde de zirconium thermiquement stable entre le Zr et le diamant. Les redresseurs fabriqués avaient: une forte densité de courant direct (1000 A par centimètre carré à 6 V), un champ critique supérieur à 7.7 MV /cm (tension de blocage 1000 V avec un courant de fuite inférieur à 1 pA), un facteur de mérite de Baliga supérieur à 244 MW par centimètre carré (la valeur la plus élevée signalée), une bonne reproductibilité indépendamment de la taille des diodes et des échantillons, la possibilité d'obtenir une hauteur de barrière inférieure à 1 eV après recuit, et une stabilité thermique supérieure à 500 ° C. / This thesis was focused on high power diamond Schottky diodes fabrication. Diamond growth and its doping are today well mastered. The advent of vertical architectures (diode active layer grown on heavily doped diamond substrate) and pseudo-vertical (stack of diode active layer and heavily doped layer grown on insulating substrate) allowed minimizing the high serial resistance, which was induced by the high ionization energy of acceptor-type dopants (boron doped diamond) preferably used in rectifiers fabrications.Besides these geometrical configurations favoring high forward currents, diamond Schottky diodes (pseudo vertical or vertical structures) were limited by: I) the quality of diode active layer altered by defects propagation from heavily doped layer thus leading to lower blocking voltage (maximum critical field of 3 MV/cm reported) than the theoretical values (theoretical values of critical field of 10 MV/cm), II) Schottky electrodes selected and the thermal and chemical stability of interfaces formed with oxygen-terminated diamond surface (required getting a Schottky contact and reducing as much as possible the interface states). Schottky metal selection and diamond surface pretreatment are crucial to get low barrier heights (low forward voltage drop and so low losses), low defects density at interfaces (low leakage current), and a thermally stable interface (high operating temperature). In this thesis, we demonstrated that a pseudo vertical diamond Schottky diode based on an oxygen-terminated surface covered by an easily oxidizable metal like zirconium (Zr) combined with an optimal heavily doped layer, allows overcoming these limitations. We first found a trade-off between the thickness of heavily doped layer and its doping level in order to minimize defects generations and thus improve the quality of diode active layer grown on the heavily doped layer (Less defects propagations). On a second hand, the Zr metallic electrodes selected gave rise to a thin zirconia interface layer which was thermally stable thus preventing the oxygen layer desorption. Zr/oxidized diamond rectifiers exhibited better features than the current state of art: a high forward current density (1000 A/cm2 at 6 V), a high critical field above 7 MV/cm (1000 V blocking voltage with a leakage current less than 1 pA), a Baliga's power figure of merit above 244 MW/cm2 (the highest value reported), a good reproducibility regardless of diodes and samples, the possibility to get a barrier heights below 1 eV by annealing, and a thermal stability higher than 500°C.

Plus de deux décennies de progrès technologiques dans le contrôle de la qualité de la croissance, du dopage et dans la conception de composants ont conduit à l'émergence de nouvelles potentialités pour des applications d'électronique de puissance. Comme le diamant représente le semi-conducteur ultime en raison de ses propriétés physiques supérieures, des efforts ont été réalisés pour développer divers dispositifs électroniques, tels que des diodes Schottky, des transistors à effet de champ (MOSFET), transistor bipolaire, jonctions pin ...Le développement d'outils de simulation capables d'anticiper les propriétés électriques des dispositifs électroniques ainsi que leur architecture pour profiter pleinement des propriétés physiques du diamant est une condition préalable à la mise au point de nouveaux composants de puissance. D'autre part, l'étude expérimentale du contact de grille, la deuxième brique élémentaire du transistor, est fondamentale en vue de développer des dispositifs de haute performance. À cet égard, on peut considérer plusieurs questions ouvertes: (i) Les outils de simulation sont-ils capables de prendre en compte les spécificités du diamant pour modéliser les composants électroniques? (ii) L'oxyde d'aluminium est-il approprié pour développer un contact de grille de transistor? (iii) Si oui, l'interface oxyde/diamant est-elle d'assez bonne qualité? (iv) La fabrication d'un MOSFET en diamant est-elle un obstacle technologique?Ce projet de doctorat, vise à répondre à ces questions et à ouvrir la voie vers la réalisation du MOSFET à canal d'inversion.Les propriétés physiques du diamant seront soulignées et aideront à comprendre pourquoi ce matériau est le semi-conducteur ultime. L'état de l'art des dispositifs en diamant sera présenté en se concentrant sur des transistors à effet de champ. L'anticipation des propriétés électriques et de l'architecture grâce à des logiciels de simulation basés sur la méthode des éléments finis constitue un sujet complémentaire. Ainsi, le besoin d'outils de simulation fiables sera présenté.D'une part, les principaux modèles mis en œuvre dans les outils de simulation seront présentés en insistant sur les propriétés électriques du diamant. Pour la simulation du MOSFET diamant, l'étude de deux briques élémentaires est nécessaire: la jonction pn et le contact de grille. Les propriétés idéales de la grille seront présentées tandis que la jonction pn servira de base pour le calibrage des paramètres physiques mises en œuvre dans le logiciel de simulation. L'influence des modèles de génération-recombinaison sur les propriétés électriques simulée de jonction pn sera discutée. Enfin, la simulation des propriétés électriques d'un MOSFET en diamant sera présentée.D'autre part, l'accent sera mis sur la fabrication et la caractérisation électrique du condensateur diamant métal-oxyde-semi-conducteur (MOSCAP). Plus précisément, le raccordement des bandes à l'interface Al2O3/diamant à terminaison oxygène (O-diamant) a été étudiée en utilisant la méthode de spectroscopie photoélectronique à rayons X. Les résultats ont permis l'établissement du diagramme de bande de l'hétérostructure Al2O3/O-diamant et démontre que l'Al2O3 est utilisable en tant qu'oxyde de grille. Ensuite, l'étude de la densité des états d'interface a révélé l'ancrage du niveau de Fermi à l'interface entre l'Al2O3 et le diamant. En outre, les courants de fuite à travers la couche d'Al2O3 seront discutés en termes d'effet tunnel assisté par pièges de trous de la couche de diamant au contact de grille. Enfin, la caractérisation électrique du premier MOSFET en diamant, effectuée au National Institute for Advanced Industrial Science and Technology (AIST) au Japon, sera présentée. Cette première tentative s'est révélée infructueuse. Néanmoins, les résultats sont très prometteurs pour le développement de diamant MOSFET étant donné que la démonstration de la réalisation du composant est clairement établie. / Over two decades of technological progresses in growth quality, doping control and device processing have led to the emergence of new potentialities for power electronic applications. As diamond represents the ultimate semiconductor owing to its superior physical properties, efforts have been conducted to develop various electronic devices, such as Schottky diodes, field effect transistors, bipolar transistor, p-i-n junctions...As a prerequisite to the development of new generation diamond power devices, on one side, is the development of simulation tools able to anticipate the device electrical properties as well as its architecture in order to take full advantage of the material physical properties. On the other hand, experimental study of the gate contact, the second building block of the transistor, is fundamental in order to develop high performance devices. In this regard, one can consider several open questions: (i) Are the simulation tools able to take into account the specificities of diamond to model electrical devices? (ii) Is the aluminum oxide suitable to develop a MOSFET gate contact? (iii) If so, is the oxide/diamond interface of good enough quality? (iv) Is the fabrication of a diamond MOSFET a technological issue?This PhD project, attend to answer these questions and pave the way towards the inversion mode MOSFET.Emphasize on the diamond physical properties will help to understand why this material is the ultimate WBG semiconductor. State of the art diamond devices will be presented focusing on field effect transistors. A complementary topic for the development of new generation diamond power device is the anticipation of device electrical properties and architecture through finite element base simulation software. Thus the need for reliable simulation tools will be presented.On one hand, the main models implemented in the simulation tools will be presented and emphasize on the diamond electrical properties will be given. For the simulation of diamond metal-oxide-semiconductor field effect transistor (MOSFET), the study of two building blocks is required: the p-n junction and the gate contact. The later ideal properties will be presented while the former will serve as a basis for the calibration of the physical parameters implemented in the finite element based software. Generation-recombination models influence on the simulated p-n junction electrical properties will be discussed. Finally, the simulation of the electrical properties of a diamond metal-oxide-semiconductor field effect transistor (MOSFET) will be shown.On the other hand, focus will be made on diamond metal-oxide-semiconductor capacitor (MOSCAP) fabrication and electrical characterization. Specifically, the interfacial band configuration of the Al2O3/oxygen-terminated diamond (O-diamond) has been investigated using X-ray photoelectron spectroscopy. The results allowed establishing the band diagram of the Al2O3/O-diamond heterostructure. Then, the electrical properties of the diamond MOSCAP will be shown. Specifically, investigation of the interface states density revealed the pinning of the Fermi level at the interface between the Al2O3 and the O-diamond. Moreover, the leakage currents through the Al2O3 layer will be discussed in terms of temperature dependent trap assisted tunneling of holes from the diamond layer to the top gate contact. Finally, the electrical characterization of the first diamond MOSFET, performed at the National Institute for Advanced Industrial Science and Technology (AIST) in Japan, will be presented. Even if this first attempt was unsuccessful, it is promising for the development of diamond MOSFET since the demonstration of the actual realization of the device is clearly established.

Orientador: Teófilo Miguel de Souza / Banca: Celso Eduardo Tuna / Banca: Osiris Canciglieri Junior / Resumo: Visando o conforto e a economia, a ciência, hoje, desenvolve tecnologias capazes de preservar o meio ambiente, diminuindo a perda de energia no processo e na utilização dessas novas técnicas, de forma a garantir um manuseio ecologicamente correto, sem deixar de atender as necessidades do homem. Uma técnica alternativa é o aproveitamento da energia proveniente do sol, que ainda é pouco explorada, podendo ser mais utilizada em coletores solares através do uso de novos materiais. Para isso, o objetivo deste trabalho é comparar o rendimento térmico e o coeficiente global de transferência de calor de materiais como cobre, alumínio e do filme de diamante CVD sobre o silício, pois essas grandezas são essenciais para a caracterização de um bom trocador de calor. Mediante pesquisa experimental foi possível observar que o filme de diamante CVD sobre o silício, mesmo com uma camada muito fina de deposição de filme, mostrou-se mais eficiente no processo de transmissão de calor quando comparado com o cobre e o alumínio / Abstract: To ensure the comfort and economy, science now develops technologies to preserve the environment by reducing energy loss process and the use of these new techniques, to ensure an environmentally friendly handling, while meeting the needs of man. An alternative technique is the use of energy from the sun, which is not explored and may be used in most solar collectors through the use of new materials. For this, the objective is to compare the thermal efficiency and overall coefficient of heat transfer materials such as copper, aluminum and CVD diamond film on silicon, since these quantities are essential for the proper characterization of a heat exchanger. Through experimental research we observed that the CVD diamond film on silicon, even with a very thin film deposition, was more efficient for heat transfer when compared with copper and aluminum / Mestre

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-08-01Bitstream added on 2014-06-13T19:39:26Z : No. of bitstreams: 1 dornelas_ln_me_guara.pdf: 431530 bytes, checksum: 5d8aa30beba39823f5403bbf59a82048 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Visando o conforto e a economia, a ciência, hoje, desenvolve tecnologias capazes de preservar o meio ambiente, diminuindo a perda de energia no processo e na utilização dessas novas técnicas, de forma a garantir um manuseio ecologicamente correto, sem deixar de atender as necessidades do homem. Uma técnica alternativa é o aproveitamento da energia proveniente do sol, que ainda é pouco explorada, podendo ser mais utilizada em coletores solares através do uso de novos materiais. Para isso, o objetivo deste trabalho é comparar o rendimento térmico e o coeficiente global de transferência de calor de materiais como cobre, alumínio e do filme de diamante CVD sobre o silício, pois essas grandezas são essenciais para a caracterização de um bom trocador de calor. Mediante pesquisa experimental foi possível observar que o filme de diamante CVD sobre o silício, mesmo com uma camada muito fina de deposição de filme, mostrou-se mais eficiente no processo de transmissão de calor quando comparado com o cobre e o alumínio / To ensure the comfort and economy, science now develops technologies to preserve the environment by reducing energy loss process and the use of these new techniques, to ensure an environmentally friendly handling, while meeting the needs of man. An alternative technique is the use of energy from the sun, which is not explored and may be used in most solar collectors through the use of new materials. For this, the objective is to compare the thermal efficiency and overall coefficient of heat transfer materials such as copper, aluminum and CVD diamond film on silicon, since these quantities are essential for the proper characterization of a heat exchanger. Through experimental research we observed that the CVD diamond film on silicon, even with a very thin film deposition, was more efficient for heat transfer when compared with copper and aluminum

The origin of diamonds, their preservation and transport to the surface have been important issues over the last decades after the acknowledgement that diamonds are xenocrysts in the host kimberlites and after the discovery of new transport media such as lamproites. Different types of diamonds -E-type diamonds, P-type diamonds- and different types of hosts - Eclogites, Peridotites- have been distinguished. Each type corresponds to particular formation criteria. Ecogitic Diamonds are mostly related to subduction processes, whereas more uncertainties remain regarding the formation of Peridotitic Diamonds. Komatiite extraction and subduction of graphite-bearing serpentinites have been proposed as the more likely processes involved in their formation. A typical mantle signature for diamonds implies a thick, cool, reduced lithosphere. The keel-shape model is the most popular. Archaean cratons are therefore the most promising exploration target and area selection will expect to follow the Clifford's Rule. However, the evidence of cratonic areas hidden under younger formations · through seismic profiles and the discovery of diamond structurally trapped outside their stability field, have increased the potential of diamondiferous areas. Preservation of diamonds inside the lithosphere requires that the mantleroot remains insulated against excessive reheating and tectonic reworking. Mantle-root friendly and mantle-root destructive structures are distinguished. Small-size cratons are usually the most promising exploration targets. Transport of diamonds to the surface is dependant on' the same criteria of preservation. Only kimberlites and lamproites have been recognized as efficient transport media. Their ascent to the surface is conditioned by a multitude of parameters, amongst them the nature of the magma, the speed of ascent, the presence of pre-existing structures in the crust and the availability of ground water in the near-surface environment. The origin of kimberlite magma probably lies near the transition zone. Mixtures of depleted asthenospheric · sources and metasomatically enriched and possibly subducted materials are likely to be at the origin of the different kimberlite magmas. Kimberlite magmatism correlates generally in time with global tectonic events, triggered by either plume activity or by subduction processes, depending of the tectonic school of thought. Kimberlite alignments have been interpreted as hotspot tracks, and kimberlite magmas as volatile-rich melts issued from the remaining plume tail. The plume head produces flood-basalts in an adjacent "thinspot" of the lithosphere, generally on the edges of the cratons. Kimberlite and lamproite ascent to the surface are unconditionally influenced by regional structures. Rift structures, ring structures, transform faults, suture zones and deep-seated faults have been mentioned as controlling or accompanying features of kimberlite magmatism. Nearsurface emplacement constraints are better understood and the ultimate shape of the intrusion(s) depends on the nature of the country rocks, the availability of ground water and the near-surface faulting pattern. The recent discovery of "fissure" kimberlites is one of the more important breakthroughs of the last decade. With a better understanding of the processes involved in diamond formation, preservation and of kimberlite emplacement, major diamond discoveries have recently increased on all the continents. Successful diamond exploration requires today an integration of all geophysical, petrologic, geochemical and structural information available. The particular study of the northwestern Australian lamproite and kimberlite fields, the Brazilian kimberlites, the easternNorth American kimberlite fields, the Lac de Gras kimberlite field, the South African rich kimberlite provinces, and the Yakutian kimberlite fields provide concrete examples of the geotectonic controls on primary diamond deposits. Area selection criteria based on the previous models and examples, are expected to yield to many more discoveries in the coming years. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

The alluvial diamond deposits along the Vaal River, between Barkly West and the Vaal-Harts confluence, have been worked for more than one century by thousands of private diggers. The diamonds are recovered from two sedimentary units of Cenozoic age, the Older Gravels and the Younger Gravels. These rest on a basement of Ventersdorp Supergroup andesites and Karoo Sequence sediments, which have been intruded by Cretaceous kimberlites. The gravels are, in turn, overlain by the Riverton Formation and the Hutton Sand. On a large scale, tectonic setting, geomorphology and palaeoclimate have played a major role in the formation of diamondiferous placers in the area under investigation. A study of the sedimentology of the Younger Gravels was carried out with the aim of acquiring an understanding of the processes responsible for the economic concentration of high quality diamonds. An investigation of facies assemblages, clast composition, clast size, palaeocurrent directions external geometry, particle morphology and led to the conclusion that the Younger Gravels were deposited in a proximal braided stream environment during high discharge. A small-scale experiment was carried out to test the efficiency of different sedimentological trap sites in concentrating kimberlite indicator minerals. The results show that the concentration of indicator minerals is dependent on the size fraction chosen, bed roughness and gravel calibre. The examination of surface features on pyrope, picroilmenite and chrome diopside from kimberlite led to the conclusion that most of these minerals are locally derived. Diamond grade variations within the Younger Gravels are influenced by a combination of factors, including bed roughness, channel width and sorting process from the source. Alluvial diamond exploration programmes must take into account the tectonic setting, the palaeoclimate, the level of erosion, the stability of the drainage system in the area as well as the presence of local trap sites in the river profile. It is concluded that the diamonds are the product of a long and complex process of erosion, reworking and concentration and are derived from Cretaceous kimberlites in the area.

The subject of this thesis is the structure of the distribution channel of gem diamonds in the world market, and certain vertical stages of the channel are singled out for more detailed study. The main stages of the distribution structure are: the mining of rough diamonds, the largely centralized sorting and distribution of the rough, the manufacture of polished diamonds in a number world centres, the distribution of the polished gems at several bourses connected with the manufacturing centres, and the operations of the local wholesalers, jewellery manufacturers, and retailers. Three areas are singled out for more detailed study: the De Beers group, which, through the Central Selling Organisation (S.C.O.), dominates the distribution of rough; the Israeli diamond industry, the largest manufacturing and distributing centre of polished diamonds; and finally, the Vancouver retail market for diamonds and diamond jewellery, which is one of the many regional branches of the largely unexplored retail end of the distribution channel. Chapter II provides a base for all that follows by describing in detail the four parameters that are basic for the appraisal of a polished diamond: colour, clarity, cut and weight. An Appendix studies the increment in the price per carat of a polished diamond as the weight of the stone increases. It is found, for example, that the traditional squaring rule gives results close to, but consistently higher than, the actual prices. Chapter III studies the prevailing modes of production in the diamond-producing countries, the historical evolution and present activities of the diamond-cutting centres, and the operations of the major trading centres. It is found that certain characteristics of the diamond-cutting industry make it an ideal field for cottage industries and small firms, working in places situated far from either the mining, the distribution, or the consumer centres. Certain recurrent patterns in the creation and development of local cutting industries are discussed. Chapter IV focuses on the development of the Israeli diamond industry. Since the first years of the State of Israel, the exportation of polished diamonds was seen as one of the main sources of foreign currency, and expansion of the industry was energetically supported by the Israeli government. The main factor limiting the growth of the industry, however, was the supply of rough diamonds. The chapter studies the changing relations between the C.S.O. and the Israeli industry, governmental protection of the industry, and the export figures. The second half of the chapter is devoted to a detailed description of the actual trading at the Israel Diamond Exchange at Ramat Gan. Chapter V studies the role of the C.S.O. in the world market, in the frame provided by the history of the De Beers group. The C.S.O.'s avowed policy of stabilizing prices for. the benefit of the industry as a whole is measured against the recent and on-going developments in the world market, characterized by steeply rising prices, speculative trading and relative shortages of rough, and some tentative explanations are proposed. Chapter VI, finally, describes the Vancouver wholesale and retail diamond markets. Since diamonds are sold by retailers almost exclusively as part of pieces of jewellery, a survey was made of Vancouver jewellery stores to find out the relative popularity and average selling prices of the main types of diamond jewellery. The method employed in this survey involved appraising and counting the jewellery pieces displayed, and direct enquiries from the salesmen. The survey was complemented by sales figures and other information on the buying preferences of Vancouver jewellers, furnished by a local wholesaler. The results were tabulated and compared with published Canadian and American data, and explanations were proposed for the differences found. The chapter concludes with a list of questions for future research on the retail market for diamond jewellery. / Business, Sauder School of / Graduate

Bibliography: p. 420-430. / In this thesis the processes that produced diamond placer deposits within closed endoreic basins along the west coast of Namibia are addressed. These deposits, first discovered in 1908, and documented by Kaiser in 1926, occur in an area of wind deflation between latitudes 26 and 28 degrees South. Salt rock weathering and aeolian abrasion has eroded elongated depressions that are up to 120 m deep, that happen to be parallel with the dominant wind flow from the south and south-southeast, which governs aeolian processes in the coastal tract. The velocity of winds from the south and south-southeast frequently averages 50 to 60 km/hour between October and March, and gusts at 80 to 90 km/hour. At these velocities, grains exceeding -1 phi (2 mm) in diameter are commonly entrained into the saltation load above stone pavement surfaces, making this an extremely active aeolian environment.