Made available in DSpace on 2015-03-26T13:35:19Z (GMT). No. of bitstreams: 1 texto completo.pdf: 7178569 bytes, checksum: b7f915a255beb77386b9a40b7b8113cd (MD5) Previous issue date: 2012-07-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work consists of the optical characterization of CdMnTe films grown on glass substrate. The films were deposited by the technique of molecular beam epitaxy (MBE) and characterized by optical spectroscopy and ellipsometry. The energy gap for films with different manganese concentration was determined. We demonstrate the increase in gap energy as concentration of manganese increases. The pronounced interference fringes observed show the good optical quality of the films grown. By ellipsometry technique we can observe the behavior of the refractive index and extinction coefficients a function of manganese concentration. We have also obtained values of sample thickness and growth rate. / Este trabalho consiste na caracterização ótica de filmes de CdMnTe crescidos sobre substratos de vidro. Os filmes foram depositados pela técnica de epitaxia por feixe molecular (MBE) e caracterizados através de espectroscopia ótica e elipsometria. Foram determinados parâmetros como gap dos filmes em função da concentração de manganês. Podemos comprovar o aumento do gap com o aumento da concentração de manganês. As franjas de interferência nos mostram a boa qualidade dos filmes crescidos. Através da técnica de elipsometria podemos observar o comportamento do índice de refração e do coeficiente de extinção em função da concentração de manganês. Foram obtidos também os valores da espessura e taxa de crescimento dos filmes.

Nesse trabalho, foi investigado um novo tipo de fotodetector de radiação infravermelha baseado em pontos quânticos de submonocamada de InAs obtidos pela técnica de epitaxia por feixe molecular (MBE, Molecular Beam Epitaxy). Suas propriedades foram comparadas com as de fotodetectores de pontos quânticos de InAs convencionais obtidos pela mesma técnica de deposição, mas no modo de crescimento Stranski-Krastanov. Medidas de corrente de escuro, de ruído, de responsividade e de absorção mostraram que, dependendo da estrutura das amostras, os dispositivos com pontos quânticos de submonocamada podem ter um excelente desempenho. / In this work, we investigated a new type of infrared photodetector based on InAs sub-monolayer quantum dots grown by molecular beam epitaxy (MBE). Their properties were compared with those of photodetectors containing conventional InAs quantum dots obtained by the same deposition technique, but in the Stranski-Krastanov growth mode. Dark current, noise, responsivity and absorption measurements have shown that, depending on the structure of the samples, the devices with sub-monolayer quantum dots can perform very well.

Os fotodetectores infravermelhos baseados em pontos quânticos (Quantum-dot Infrared Photodetectors, QDIPs) surgiram recentemente como uma nova tecnologia para a detecção de radiação infravermelha. Comparados com fotodetectores mais convencionais baseados em poços quânticos (Quantum-well Infrared Photodetectors, QWIPs), as suas vantagens se originam no confinamento tridimensional de portadores e incluem a sensibilidade intrínseca à incidência normal de luz, um maior tempo de vida dos portadores fotoexcitados e uma baixa corrente de escuro, que devem permitir o funcionamento dos dispositivos acima das temperaturas criogênicas. No presente trabalho, a técnica de epitaxia por feixe molecular (Molecular-Beam Epitaxy - MBE) foi usada para crescer várias amostras de QDIPs de InAs/GaAs com o objetivo de estudar a inuência dos parâmetros estruturais destes dispositivos. Após o crescimento, as amostras foram processadas em pequenas mesas quadradas por técnicas de litografia convencional e, então, caracterizadas. As propriedades ópticas e eletrônicas dos dispositivos foram verificadas para temperaturas a partir de 10 K. Com o objetivo de realizar medidas eletrônicas de alta qualidade, janelas de Ge e cabos com conectores de baixo ruído para baixa temperatura foram empregados. As curvas de corrente de escuro, as curvas de responsividade com corpo negro (fotocorrente), as medições do ruído com uma analisador de sinais e as respostas espectrais por FTIR (Fourier Transform Infrared) forneceram um conjunto completo de informações sobre os dispositivos. As figuras de mérito dos nossos melhores dispositivos permitiram também, determinar a probabilidade de captura e o ganho fotocondutivo. Com o intuito de compreender a relação entre as dimensões físicas dos pontos quânticos e as características de funcionamento dos QDIPs, desenvolveu-se um cálculo dos estados eletrônicos de da função de onda de um elétron confinado em um ponto quântico de InxGa1-xAs em formato de lente, envolvido em uma matriz de GaAs, com massas efetivas dependentes da posição. Esse modelo leva em conta o efeito da tensão assim como o gradiente de In dentro do ponto quântico, resultante do forte efeito de segregação presente em um sistema de InxGa1-xAs/GaAs. Diferentes perfis de segregação foram testados com o nosso modelo teórico com vista a proporcionar o melhor ajuste os nossos dados experimentais. / Quantum-dot Infrared Photodetectors (QDIPs) recently emerged as a new technology for detecting infrared radiation. Compared to more conventional photodetectors based on quantum wells (QWIPs), their advantages originate from the three-dimensional confinement of carriers and include an intrinsic sensitivity to normal incidence of light, a longer lifetime of the photoexcited carriers and a lower dark current which should hopefully allow their operation close to room temperature. In the present work, molecular-beam epitaxy (MBE) was used to grow several InAs/GaAs QDIP samples in order to analyse the influence the structural properties of such devices. After the growth, the samples were processed into small squared mesas by conventional lithography techniques and fully characterized. The optical and electrical properties of the devices were checked as a function of temperature using Ge optical windows and all the connectors and low-temperature/low-noise cables needed to perform high quality low-level electrical measurements. Dark-current curves, Responsivity (photocurrent) data with a black body, noise measurements with a signal analyzer and spectral responses by FTIR provided a full set of information about the devices. The figures of merit of our best devices allowed us also to determine the capture probability and the photoconductive gain. In order to understand the relationship between the physical dimensions of the quantum dots and the operating characteristics of the QDIPs, we developed a position-dependent effective-mass calculation of the bound energy levels and wave function of the electrons confined in lensshaped InxGa1-xAs quantum dots embedded in GaAs, taking into account the strain as well as the In gradient inside the quantum dots which is due to the strong In segregation and intermixing present in the InxGa1-xAs/GaAs system. Different In profiles inside the quantum dots were tested with our new theoretical model in order to provide the best _t to our experimental data.

Made available in DSpace on 2014-10-09T12:44:29Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:27Z (GMT). No. of bitstreams: 1 06872.pdf: 4167574 bytes, checksum: 52f6a850bb9e5261861d1ba84fb83a28 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Dans le contexte de la protection périphérique des composants de puissance en GaN, nous avons exploré une voie originale pour réaliser l'homo-épitaxie localisée de GaN de type p, reposant sur une approche Vapeur-Liquide-Solide (VLS). Le cycle de croissance comprend 3 étapes successives. Dans un premier temps, du Ga est déposé par MOCVD, formant un réseau de gouttelettes de diamètres submicrométriques. Puis, du Mg est incorporé aux gouttelettes à partir de la phase gazeuse, en utilisant le précurseur (MeCP)2Mg. Enfin, les gouttelettes de Ga-Mg sont nitrurées à 500-700°C sous un flux de NH3 dilué dans un gaz porteur. À l'issue d'un cycle complet de croissance, on obtient systématiquement un réseau de plots et/ou d'anneaux de GaN, bien séparés. L'augmentation de la teneur en Mg dans les gouttes favorise un mécanisme de croissance purement VLS, à l'interface Liq/Sol (formation de plots), plutôt qu'une croissance le long de la ligne triple (formation d'anneaux). Ces structures de GaN présentent un caractère homo-épitaxial, mais une plus forte défectuosité que leur germe. En utilisant une approche multi-cycles, nous avons pu élaborer des films de GaN:Mg présentant des concentrations en Mg très élevées, contrôlables entre 3.1019 cm-3 et 8.1021 cm-3. Cependant, de fortes concentrations en impuretés C, H et O ont également été détectées dans ces films. Diverses voies ont été explorées, sans succès, pour tenter de réduire la contamination en O, d'un niveau rédhibitoire pour l'obtention d'un dopage de type p. En pratique, les films de GaN:Mg obtenus apparaissent très conducteurs de type n, pour des dopages au Mg modérés, et semi-isolants aux plus forts dopages. Différents matériaux de masques ont été testés en vue de localiser la croissance / For peripheral protection of GaN power electronics devices, we have explored a new approach for performing localized homo-epitaxy of p-doped GaN, by implementing Vapor-Liquid-Solid (VLS) transport. The growth cycle includes three successive steps. At first, Ga is deposited onto the seed surface by MOCVD from TEG, resulting in an array of Ga droplets with submicrometric diameters. Then, Mg is incorporated into the droplets from the gas phase, using (MeCP)2Mg precursor. In the last step, Ga-Mg droplets are nitridated at 500-700°C in flowing ammonia diluted in a carrier gas.After one complete growth cycle, a network of well separated submicrometric GaN dots or ring-shaped features is systematically obtained. Increasing the Mg incorporation into the droplets drastically influences the growth mode, promoting a pure VLS growth mechanism, at the Liquid/Solid interface, versus growth at the triple line. Such GaN structures show a homo-epitaxial relationship with the seed, but a higher crystalline imperfection. Using a multi-cycles approach, GaN films could be obtained, with very high Mg concentrations tunable from 3.1019 to 8.1021 cm-3. Nevertheless, O, C and H impurities are also incorporated at high levels. Various approaches have been vainly investigated to try reducing O contamination level, prohibitive for obtaining p-type material. Actually, as-grown GaN:Mg films are n-type and highly conductive, for moderate Mg concentrations, and become semi-insulating at highest doping levels. Various masking materials have been tested for growth localization purpose

Die Bedeutung von keramischen Materialien mit funktionalen Eigenschaften ist über die letzten Jahrzehnte kontinuierlich gestiegen. Ein besonderes Interesse liegt dabei in der elektronischen Speicherung von Informationen. Die Realisierung war jedoch lange Zeit problematisch, da die erforderlichen Feldstärken, die notwendig sind, um die Polarisation zu schalten, für Massivmaterialien zu hoch sind. Heutzutage ist dies dank moderner Dünnschichttechnologien kein Problem mehr, so dass nichtflüchtige ferroelektrische Datenspeicher kommerziell verfügbar sind. Aufgrund der ausgezeichneten dielektrischen und elektromechanischen Eigenschaften von ferroelektrischen Materialien werden diese auch für Anwendungen in Aktuatoren, Kondensatoren oder mikro-elektro-mechanischen Systemen verwendet. Neben den klassischen Ferroelektrika wie Pb(Zr,Ti)O3 spielen dabei vor allem Relaxor-Ferroelektrika wie Pb(Mg1/3Nb2/3O3-PbTiO3 (PMN-PT) eine entscheidende Rolle. Eine weitere sehr interessante funktionale Eigenschaft von ferroelektrischen Materialien, die besonders in den letzten zehn Jahren das Forschungsinteresse geweckt hat, ist der elektrokalorische Effekt (electro caloric effect, ECE). Besonders hohe ECE konnten in der Vergangenheit mit Blei-basierenden Materialien, wie beispielsweise PMN-PT, erzielt werden. Um den Einfluss der Struktur auf die funktionalen Eigenschaften zu untersuchen ist es vorteilhaft, mit texturierten Schichten zu arbeiten. Als Materialsystem wurde in dieser Arbeit PMN-PT verwendet, da dieses besonders gute ferroelektrische und elektrokalorischen Eigenschaften zeigt und es aufgrund der vielfältigen veröffentlichten Untersuchungen als Modellsystem genutzt werden kann. Als geeignete Herstellungsmethode von Dünnschichten komplexer Oxide hat sich die gepulste Laserabscheidung herausgestellt, die auch in dieser Arbeit genutzt wurde. Die Schwerpunkte der strukturellen Untersuchungen beschäftigen sich mit der Stabilisierung der Perowskit-Phase des PMN-PT, der detaillierten Aufklärung des Gefüges sowie der Realisierung von Schichten mit unterschiedlicher Orientierung und auf verschiedenen Substratmaterialien. Hinsichtlich der funktionalen Eigenschaften wird auf den Einfluss der Pyrochlor-Phase auf die Ferroelektrizität, die Anisotropie der ferroelektrischen und elektrokalorischen Eigenschaften sowie auf eine Möglichkeit der direkten Messung der elektrokalorischen Temperaturänderung von PMN-PT Dünnschichten eingegangen.

No description available.

Ce travail de thèse porte sur l’étude de la croissance de nitrure d’éléments V sur des substrats de silicium (Si) (111) micro et nano-structuré. Son but est de simplifier l’hétéroépitaxie de GaN sur Si tout en gardant une qualité de matériau à l’état de l’art. L’originalité de ce travail repose sur la combinaison avantageuse de deux techniques de croissance : NH3-EJM et EPVOM. Nous avons d’abord évalué l’intérêt du silicium poreux (SiP) pour confiner les fissures et l’utiliser comme couche compliante. Malgré les changements structuraux s’opérant dans le SiP lorsqu’il est porté aux hautes températures nécessaires pour la croissance épitaxiale, nous avons pu démontrer la croissance de GaN de bonne qualité en ajoutant une couche de Si épitaxiée avant la croissance des nitrures d’éléments V. Puis, nous avons étudié la croissance de GaN dans des ouvertures réalisées dans un masque diélectrique déposé sur le substrat de Si. Cette approche a permis d’obtenir des motifs de GaN non fissurés et de bonne qualité cristalline en utilisant des conditions de croissance optimisées. L’analyse des contraintes sur les motifs de GaN indique une distribution en U où le maximum de la contrainte en tension est mesuré au centre des motifs ; cette contrainte se relaxe graduellement vers les bords libres des motifs. Enfin, une comparaison avec la croissance sur des mesas de Si gravé est proposée. Nous montrons que la croissance dans des ouvertures permet à la fois d’obtenir une couche de GaN uniformément épitaxiée sur les motifs ainsi que d’obtenir une plus faible courbure des substrats après croissance. Enfin, des LEDs ont pu être fabriquées à partir de GaN épitaxié sur substrat masqué. / This work deals with the growth of III-Nitrides on micro and nano-patterned silicon (111) substrates. The main goal is to simplify the heteroepitaxy of GaN on Si while keeping state of the art III-nitride materials. The originality of this work is to combine the advantages of both NH3-MBE and MOCVD growth techniques. We firstly evaluated the interest of porous silicon to confine cracks and to behave as a compliant substrate. Despite the issues regarding the structural changes of the porous silicon with the high temperatures necessary for the epitaxial growth of GaN, we demonstrated the growth of high quality GaN layers by growing a silicon layer of few tens of nanometers prior to III-nitride layers. Then, we studied the windowed growth of GaN on silicon substrates masked with dielectric films. We found that this approach can produce high quality crack free GaN (2µm thick) patterns with size up to 500x500 µm² with a dislocation density of few 108cm-2. Furthermore, crack statistics reveal that a large amount of crack free patterns can be obtained using optimized conditions. Stress analyses of GaN patterns demonstrate a “U-shape” stress distribution where the maximum tensile stress is found in the middle of the patterns and gradually decreases towards the pattern edges. Finally, a comparison with mesa patterned silicon substrates is proposed with identical grown structures. We found that windowed growth is more advantageous regarding growth uniformity and substrate bowing. As a result of this work, LEDs have been fabricated using GaN grown on masked substrates.

abstract: III-V-bismide semiconductor alloys are a class of materials with applications in the mid and long wave infrared spectrum. The quaternary alloy InAsSbBi is attractive because it can be grown lattice-matched to commercially available GaSb substrates, and the adjustment of the Bi and Sb mole fractions enables both lattice constant and bandgap to be tuned independently. This dissertation provides a comprehensive study of the surface morphology and the structural and chemical properties of InAsSbBi alloys grown by molecular beam epitaxy. 210 nm thick InAsSbBi layers grown at temperatures from 280 °C to 430 °C on (100) on-axis, (100) offcut 1° to (011), and (100) offcut 4° to (111)A GaSb substrates are investigated using Rutherford back scattering, X-ray diffraction, transmission electron microscopy, Nomarski optical microscopy, atomic force microscopy, and photoluminescence spectroscopy. The results indicate that the layers are coherently strained and contain dilute Bi mole fractions. Large surface droplets with diameters and densities on the order of 3 µm and 106 cm-2 are observed when the growth is performed with As overpressures around 1%. Preferential orientation of the droplets occurs along the [011 ̅] step edges offcut (100) 1° to (011) substrate. The surface droplets are not observed when the As overpressure is increased to 4%. Small crystalline droplets with diameters and densities on the order of 70 nm and 1010 cm-2 are observed between the large droplets for the growth at 430°C. Analysis of one of the small droplets indicates a misoriented zinc blende structure composed of In, Sb, and Bi, with a 6.543 ± 0.038 Å lattice constant. Lateral variation in the Bi mole fraction is observed in InAsSbBi grown at high temperature (400 °C, 420 °C) on (100) on-axis and (100) offcut 4° to (111)A substrates, but is not observed for growth at 280 °C or on (100) substrates that are offcut 1° to (011). Improved crystal and optical quality is observed in the high temperature grown InAsSbBi and CuPtB type atomic ordering on the {111}B planes is observed in the low temperature grown InAsSbBi. Strain induced tilt is observed in coherently strained InAsSbBi grown on offcut substrates. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22449号 / 工博第4710号 / 新制||工||1736(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 川上 養一, 教授 野田 進, 教授 山田 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM