Este trabalho apresenta o estudo da influência do tensionamento mecânico (strain) no efeito de abaixamento de barreira induzido pelo dreno (DIBL) em dispositivos SOI FinFETs de porta tripla com e sem crescimento seletivo epitaxial. Também é analisada a influência do uso de crescimento seletivo epitaxial nesses dispositivos em relação ao efeito de canal curto mencionado. O uso de transistores verticais de múltiplas portas tem permitido a continuidade do escalamento dos dispositivos, apresentando melhora nos níveis de corrente bem como a supressão dos efeitos de canal curto. No entanto, ao reduzir a largura do canal, aumenta-se a resistência total do transistor, diminuindo seu desempenho. A fim de melhorar essa característica, as técnicas de tensionamento mecânico e crescimento de fonte e dreno tem sido empregadas. No primeiro caso, ao se deformar mecanicamente a estrutura do canal, altera-se o arranjo das camadas eletrônicas que ocasiona o aumento da mobilidade dos portadores. Conseqüentemente, a corrente aumenta tal como a transcondutância do dispositivo. A técnica de crescimento de fonte e dreno chamada de crescimento seletivo epitaxial (SEG) tem como finalidade reduzir ainda mais a resistência elétrica total da estrutura, uma vez que a área dessas regiões aumenta, possibilitando o aumento das áreas de contato, que são responsáveis pela maior parcela da resistência total. Esse trabalho baseia-se em resultados experimentais e simulações numéricas tridimensionais que analisam o comportamento dos transistores com as tecnologias acima apresentadas em função do efeito de DIBL. / This work presents a study about the influence of strain in the drain induced barrier lowering effect (DIBL) in triple gate SOI FinFETs. Also it is analyzed the selective epitaxial growth used in that structures, comparing their behavior in relation to DIBL effect. Using the vertical multi-gate devices become possible the downscale whereas they present higher current level and suppressed short channel effects. However, reducing the channel width, the transistors total resistance increases and consequently its performance decreases. In order to improve this feature, the strained technology and the Source/Drains growth technique has been employed. In the first case, the mechanical deformation causes a change in the electron shell, which improves the carrier mobility. Consequently, the current level and the transconductance also improve. The selective epitaxial growth technique aims to reduce the devices total resistance since these regions areas increase, allowing large contacts which are responsible for the main parcel of the total resistance. This work is based on experimental results and tridimensional simulations that analyze the transistor behavior using the technologies above presented as a function of DIBL effect.

Des films minces d’oxydes de cuivre (Cu2O, Cu4O3 et CuO) ont été déposés à température ambiante sur des substrats en verre et en silicium par pulvérisation magnétron réactive. Une attention particulière a été portée à l’influence des conditions de synthèse (débit d’oxygène et pression totale) sur la structure et l’orientation préférentielle des dépôts. La pression totale est le paramètre principal influençant la texture des films de Cu2O et de Cu4O3. En revanche l’orientation préférentielle des films de CuO est contrôlée par le débit d’oxygène. Pour des films de Cu2O et de Cu4O3, un phénomène de croissance épitaxique locale (CEL) a été mis en évidence. Il résulte de l’utilisation d’une première couche qui joue le rôle d’une couche de germination lors du processus de croissance. Ainsi, les films peuvent croître avec une texture donnée indépendamment de leurs conditions de synthèse. Cet effet de CEL a été mis à profit pour élaborer des films biphasés (Cu2O + Cu4O3) qui présentent une microstructure originale. L’augmentation de la transmittance optique et du gap optique de films de Cu2O a été rendue possible par des traitements thermiques dans l’air qui permettent de diminuer la densité de défauts dans les films. Finalement, les propriétés optiques et la structure électronique des oxydes de cuivre qui ont été calculées par la méthode GW sont en accord avec des résultats expérimentaux obtenus par absorption optique, photoémission et spectroscopie de perte d’énergie des électrons. / Copper oxide (Cu2O, Cu4O3 and CuO) thin films have been deposited on unmatched substrates by sputtering at room temperature. The influence of oxygen flow rate and total pressure on the film structure and preferred orientation has been studied. The total pressure is a relevant parameter to control the texture of Cu2O and Cu4O3 films, while the oxygen flow rate is effective to tune the preferred orientation of CuO films. Local epitaxial growth, where epitaxial relationship exists in columns of sputtered films, has been observed in Cu2O and Cu4O3 films by using a seed layer. The seed layer will govern the growth orientation of top layer via the local epitaxy, independently of the deposition conditions of top layer. Unusual microstructure that both phases have the vertically aligned columnar growth has been evidenced in biphase Cu2O and Cu4O3, which may relate to the local epitaxial growth of Cu2O. The lower resistivity than that in single phase films has been observed in this biphase film. Annealing in air can increase the transmittance of Cu2O films in visible region by the reduction of the impurity scattering, while the optical band gap is enlarged due to the partial removal of defect band tail. The optical properties and electronic structure of copper oxides calculated by GW approach with an empirical on-site potential for Cu d orbital, are in good accordance with experimental results from optical absorption, photoemission and electron energy loss spectroscopies

Graphene nanoribbons (GNRs) are considered as major building blocks of future carbon-based electronics, in which the termination of the edges essentially defines the electronic properties. Theoretical predictions, such as tunable band gaps in armchair orientated GNRs, and the existence of topologically protected metallic states located at zigzag edges, make them a potential candidate for transistor applications as well as a new class of fully coherent devices. In this context, the fabrication of high-quality GNRs with precise edge geometries is of great interest. Atomistic details and the interaction with its support crucially influence and determine the charge propagation within such graphene nanostructures. Hence, the understanding of transport mechanisms on the nanoscale is indispensable in order to integrate GNRs in future nanoelectronics. This thesis presents a detailed study of the sublimation-assisted growth of different types of self-assembled GNRs on SiC crystals using scanning probe, electron microscopy, and electron diffraction experiments. First, natural SiC steps will be shown to trigger the formation of µm-long epitaxial monolayer GNRs (ML-GNRs), which laterally expand on the flat SiC(0001) surface. These ribbons can be transformed into bilayer GNRs (BL-GNRs) by annealing in air. During this process, oxygen-intercalation takes place, forming an oxide layer below the BL-GNRs. Charge transfer into the oxide layer results in strong p-type doping. Based on local multi-probe experiments, ML-GNRs and BL-GNRs revealed 1D diffusive transport characteristics inherent in the comparably high charge carrier densities in both types of ribbon. Moreover, temperature activated interlayer hopping was identified as an effective transport mechanism in BL-GNRs. Graphene nanoribbons grown on pre-processed SiC sidewalls exhibited superior crystalline and electronic quality on wafer-scales. Sidewalls aligned parallel to the [11-20] SiC direction are composed of a periodic array of mini-terraces hosting several approximately (3+-1) nm wide armchair terminated GNRs (ac-GNRs) at their step edges. By using a combined nanoprobe and conductive atomic force microscopy study, ac-GNRs revealed semi-conducting transport characteristics with band gaps of ~300 meV. Such debunching effects can be suppressed in sidewalls along the [1-100] SiC direction. Here, the graphene completely overgrows the sidewall resulting in ~40 nm wide freestanding zigzag GNRs (zz-GNRs). A robust ballistic edge channel was found to be the hallmark of zz-GNRs, which persists on µm-scales at room temperature suggesting the existence of a perfectly conducting channel. However, the roughness of the SiC and the mesa sidewalls limit the charge propagation in this edge mode due to strong short-range interactions. Moreover, ballistic transport was independently proven by utilizing non-invasive and invasive voltage probes. Tuning of the invasiveness was achieved using cleaning procedures of the tips, which lead to a subsequent decrease of contact resistance due to the removal of oxide from the tip surface. The measured resistance of the ballistic conductor was shown to be directly dependent on the invasiveness of the tips, pointing out the importance of the interplay between the probes and the GNR. Finally, spatially-resolved nanoprobe experiments with ultra-small probe spacings revealed several quantized conduction plateaus across zz-GNRs. These plateaus were attributed to edge and bulk transport channels, respectively. Based on tight-binding calculations, the occurrence of spatially-segregated ballistic channels was explained by transversal electric fields originating from asymmetric edge terminations on both sides of the GNR. These findings highlight that edge morphology is an essential parameter in order to understand electronic transport in GNRs. / Nanometerbreite Streifen aus Graphen, sogenannte Graphen-Nanoribbons (GNRs), gelten als wichtiges Bauelement in zukünftigen, kohlenstoffbasierten Elektroniken. Dabei sind die elektronischen Eigenschaften der GNRs wesentlich durch die Geometrie ihrer Kanten bestimmt. Basierend auf theoretischen Modellen, werden skalierbare Bandlücken in armchair-GNRs, sowie lokalisierte, metallische Kantenzustände in zigzag-GNRs vorhergesagt. Diese Eigenschaften könnten für Transistoranwendugen oder sogar für die Realisierung von Bauelementen, die auf kohärentem Ladungstransport basieren, genutzt werden. Dementsprechend ist die Herstellung hochwertiger GNRs mit präzisen Kantengeometrien sowie das Verständnis der zugrundeliegenden Transportmechanismen von großem Interesse. Die vorliegende Arbeit umfasst eine detaillierte Charakterisierung der strukturellen Eigenschaften verschiedener GNR-Typen, die mittels Sublimationsepitaxie auf SiC Kristallen hergestellt wurden. Es wird gezeigt, dass sich μm-lange Monolagen-GNRs (ML-GNRs) an natürlichen SiC Stufenkanten ausbilden, die durch Tempern an Luft zu Bilagen-GNRs (BL-GNRs) transformiert werden können. Während des Temperns findet die Interkalation von Sauerstoff statt, sodass sich unterhalb des BL-GNRs eine Oxidschicht bildet. Der Ladungstransfer in diese Oxidschicht führt zu einer starken p-Dotierung. Lokale Transportmessungen mittels eines 4-Spitzen STM/SEM zeigen, dass sowohl ML-GNRs als auch BL-GNRs 1D diffuse Leiter sind, deren Transporteigenschaften durch die hohen Ladungsträgerdichten dominiert werden. Darüber hinaus wird gezeigt, dass das thermisch aktivierte Tunneln zwischen Graphenlagen ein effektiver Transportmechanismus in BL-GNRs ist. Graphen-Nanoribbons, die durch präferenzielles Wachstum auf SiC-Seitenwänden hergestellt wurden, zeichnen sich durch herausragende strukturelle sowie elektronische Eigenschaften aus. Seitenwände parallel zur [11-20] Richtung wiesen hierbei eine periodische Struktur von Mini-Terrassen auf, an deren Stufen sich mehrere (3 ± 1) nm breite armchair-GNRs (ac-GNRs) ausbilden. Durch die Kombination von 4-Spitzen STM/SEM und Rasterkraftmikroskopie mit leitfähigen Spitzen wurde festgestellt, dass ac-GNRs halbleitende Eigenschaften aufweisen. Die Größe der ermittelten Bandlücken beträgt ∼ 300 meV. Das Zerfallen in Mini-Terrassen kann bei Seitenwänden entlang der [1-100] SiC Richtung unterdrückt werden. Hierbei wird die Seitenwand vollständig vom Graphen überwachsen, sodass sich ∼ 40 nm breite zigzag-GNRs (zz-GNRs) ausbilden. Diese zeichnen sich durch einen robusten, ballistischen (Kanten-) Transportkanal aus, der bei Raumtemperatur auf μm-Skalen nachweißbar ist. Lediglich Rauigkeiten des Substrats sowie der Seitenwände, die als starke Streuzentren dienen, limitieren die Ausbreitung der Ladungsträger in diesem Kantenzustand. Der ballistische Transport von Ladungsträgern in zz-GNRs wurde unabhängig, mit Hilfe von nicht-invasiven und invasiven Spannungskontakten (STM-Spitzen) nachgewiesen. Die Invasivität der Kontakte wurde durch spezielle Reinigungsverfahren der Spitzen verändert, die zu geringeren Kontaktwiderständen führten. Hierbei wird gezeigt, dass der gemessene Widerstand des ballistischen Leiters direkt von der Invasivität der Spitzen abhängt. Dies deutet darauf hin, dass die Interaktion zwischen Messspitze und GNR bezüglich der Transporteigenschaften von großer Bedeutung ist. Abschließend werden mittels ortsaufgelöster Transportmessungen mit ultrakleinen Spitzenabständen mehrere, quantisierte Leitungskanäle detektiert, die sich räumlich über die Breite der zz-GNRs verteilen. Diese Kanäle können jeweils Kanten- und Volumen-Zuständen zugeordnet werden. Gestützt durch tight-binding-Berechnungen werden die quantisierten Transportkanäle durch transversale elektrische Felder erklärt, die durch asymmetrische Bindungsverhältnisse der Kanten erzeugt werden. Diese Ergebnisse unterstreichen, dass die Kantenmorphologie ein wesentlicher Parameter ist, um den elektronischen Transport in GNRs zu verstehen.

No description available.

In this thesis, the effect of surfactants (Bi /Sb) on GaAs(111) is explored, particularly in regards to modifying the surface morphology and growth kinetics. Both molecular beam epitaxy (MBE) and metal-organic chemical vapour deposition (MOCVD) techniques are discussed in this context. InAs/GaAs(111) quantum dots (QDs) have been promoted as leading candidates for efficient entangled photon sources, owing to their high degree of symmetry (c_3v). Unfortunately, GaAs(111) suffers from a defect-ridden homoepitaxial buffer layer, and the InAs/GaAs(111) material system does not natively support Stranski{Krastanov InAs QD growth. Surfactants have been identified as effective tools to alter grown surface morphologies and growth modes, potentially overcoming these obstacles, but have yet to be studied in detail in this context. For MBE, it is shown that Bi acts as a surfactant when employed in GaAs(111) homoepitaxy, and eliminates defects/hillocks, yielding atomically-smooth surfaces with step-flow growth, and RMS roughness values of 0.13 nm. The effect is more pronounced as the Bi flux increases, and Bi is suggested to be increasing adatom diffusion. A novel reflection high energy electron diffraction (RHEED)-based experiment was also designed and performed to measure the desorption activation energy (U_Des) of Bi on GaAs(111), yielding U_Des = 1.74 ± 0.38 eV. GaAs(111) homoepitaxy was also investigated using MOCVD, with GaAs(111)B exhibiting RMS roughness values of 0.09 nm. Sb is shown to provoke a morphological transition from plastically-relaxed 2D to 3D growth for InAs/GaAs(111)B, showing promise in its ability to induce QDs. Finally, simulations for GaAs-based quantum well (QW) photoluminescence were conducted, and such QWs are shown to potentially produce very sharp linewidths of 3.9 meV. These results enhance understanding of Bi surfactant behaviour on GaAs(111) and can open up its use in many technological applications, paving the way for the realization of high efficiency/viable QD entangled photon sources. / Thesis / Master of Applied Science (MASc)

No description available.

[pt] Substratos de germânio (Ge) são utilizados para o crescimento de dispositivos optoeletrônicos III-V, como células solares. Porém, o Ge é uma matéria-prima crítica devido à sua disponibilidade limitada. Além disso, o substrato de Ge representa cerca de 30-40 por cento dos custos totais de uma célula solar de junção tripla. Neste trabalho, foram crescidas amostras e células solares III-V sobre substratos de Ge com diferentes tecnologias (tec). Três diferentes tecs foram investigadas: 1) utilizando substratos de Ge com camadas porosas para crescer materiais III-V, sendo que a camada porosa é retirada para que o substrato possa ser reutilizado; 2) utilizando substratos mais finos e com menos processos de finalização da superfície, o que a deixa mais rugosa comparada a substratos comerciais; 3) substituindo o substrato de Ge por substratos alternativos que compreendam outros elementos, como um substrato de Si onde é depositado um buffer metamórfico de SiGe, no qual o parâmetro de rede foi ajustado até o chegar no de Si0.1Ge0.9. Os substratos utilizados não são perfeitos como os substratos comerciais de Ge e podem gerar defeitos nas camadas de III-V subsequentes. Para investigar a influência desses substratos nas camadas III-V foram crescidas heteroestruturas duplas (HED) de AlGaInAs/GaInAs nos substratos das tecs 1 e 2 e HED de AlGaAs/GaAs nos substratos da tec 3. Suas propriedades foram avaliadas com AFM para obter a rugosidade média quadrática e possíveis defeitos da superfície, catodoluminescência para estimar a densidade de defeitos na estrutura e Electron Channeling Contrast Imaging para identificar os tipos de defeitos encontrados com CL. Além disso, para as amostras crescidas sobre os substratos tec 1, suas composições e espessuras foram investigadas por XRD e com fotoluminescência resolvida no tempo avaliou-se o tempo de vida dos elétrons. Nos substratos das tecs 2 e 3 também foram crescidas células solares de junção tripla, que foram processadas e caracterizadas por curvas I-V e EQE. Os resultados obtidos com todas as tecs levam a uma perspectiva otimista para um futuro com células solares mais baratas e que utilizem menos Ge. / [en] Germanium (Ge) substrates are used for the growth of III-V optoelectronic devices such as solar cells. However, Ge is a critical raw material due to its limited availability. Furthermore, Ge substrate accounts for about 30-40 percent of the total costs of a triple junction solar cell. In this work III-V samples and solar cells were grown on Ge substrates with different technologies (techs). Three different techs were investigated: 1) using Ge substrates with porous layers to grow III-V materials, in which the porous layer is removed so that the substrate can be reused; 2) using thinner substrates and with fewer surface finishing processes, which makes it rougher compared to commercial substrates; 3) replacing the Ge substrate with alternative substrates that comprise other elements, such as a Si substrate where a metamorphic SiGe buffer is deposited, in which the lattice parameter is gradually adjusted until it reaches Si0.1 Ge0.9. The substrates used are not as perfect as commercial Ge substrates and can generate defects in the subsequent III-V layers. To investigate the influence of these substrates on III-V layers, double heterostructures (DH) of AlGaInAs/GaInAs were grown on the substrates of techs 1 and 2 and DH of AlGaAs/GaAs on the substrates of tech 3. Their properties were evaluated with AFM to obtain the root mean square roughness and possible surface defects, cathodoluminescence to estimate the density of defects in the structure and Electron Channeling Contrast Imaging to identify the types of defects found with CL. Furthermore, for samples grown on tech 1 substrates, the compositions and thicknesses were evaluated by XRD, and with time-resolved photoluminescence, the lifetime of the electrons was evaluated. Triple junction solar cells were also grown on techs 2 and 3 substrates, which were processed and characterized by I-V and EQE curves. The results obtained with all tecs lead to an optimistic perspective for a future with cheaper solar cells that use less Ge.

No description available.

Le sujet de thèse s’inscrit dans le cadre des stratégies visant à organiser des nanostructures, plus particulièrement les stratégies visant à augmenté la densité d’information dans les médias magnétique. Les techniques de synthèse en chimie douce utilisés au LPCNO-INSA on permet d’élaborer des nano-bâtonnets monocristallins de cobalt dont les propriétés ferromagnétiques en termes d’anisotropie et d’aimantation présentent un grand intérêt pour des applications dans le domaine du stockage magnétique. La maitrise de la croissance de ces nano-bâtonnets de Co organisés perpendiculairement sur un substrat peut permettre de réaliser un média de forte densité. Nous avons dans un premier temps vérifié la croissance perpendiculaire de nano bâtonnets de cobalt monocristallins sur une couche continue de Pt (111) épitaxiée sur un substrat de saphir (Al2O3) et montré que cette combinaison de deux types de dépôts (physique et chimique) donne effectivement lieu à un réseau dense et perpendiculaire de bâtonnets de Co. Pour but d’organiser cette croissance et découpler physiquement les bâtonnets de Co nous avons alors étudié la croissance de ces bâtonnets de Co sur des îlots 3D métalliques de Pt et de Co.En première partie nous avons étudié la structure cristalline, La morphologie, les distributions en taille et l’état des contraintes des îlots de Pt et Co déposée sur la surface (0001) du saphir et la surface (001) du MgO par pulvérisation cathodique. Et en deuxième partie, nous avons étudié la croissance des nano bâtonnets de Co sur les ilots de Pt et de Co maitrisés dans l’étape précédente / The subject of this thesis is to be part of strategies in order to organize nanostructures, particularly strategies to increase information density in magnetic media. The synthesis techniques used in chemistry (LPCNO-INSA laboratory) is allowed to develop monocrystalline nanorods of cobalt whose ferromagnetic properties in terms of anisotropy and magnetization present a great interest for applications in the field of magnetic storage. The success in controling the growth of these nanorods arranged perpendicularly on a substrate can lead to achieve a high density media. We tested the perpendicular growth of monocrystalline nanorods of cobalt on a continuous and epitaxial layer of Pt (111) grown on a substrate of sapphire (Al2O3) and showed that this combination of two types of deposits (physical and chemical) give actually a dense and perpendicular network of Co nanorods. In the aim to organizing this growth and decoupling physically the nanorods we studied the growth of these Co nanorods on 3D metallic islands of Pt and Co. In the first part we studied the crystal structure, morphology, size distributions and the stress state of Pt and Co islands deposited on the surface (0001) of sapphire and (001) surface of MgO by sputtering. And in the second part, we studied the growth of Co nanorods on a Pt and Co islands mastered in the previous step

Cette thèse concerne une nouvelle méthode chimique de croissance par germes qui peut produire des assemblés de nanostructures métalliques epitaxiées sur des surfaces macroscopiques cristallines qui agissent comme germes. Cette approche permet d’obtenir des assemblés bien organisées en échelle centimétrique de nanofils métalliques de Co, qui sontmonocristallins, monodisperses de diamètres inferieurs à 10nm et qui ont une orientation perpendiculaire. Ils ont une anisotropie magnétique perpendiculaire et sont intéressantes pour des applications d’enregistrement magnétique à très haute densité. L’extension de cette méthode au fer donne des films nanostructurés de fer. L’orientation des nanostructures sur le support solide dépend de l’orientation cristallographique du substrat, alors que leur morphologie est dictée par la composition de la solution. Cet objectif a été atteint grâce à des études parallèles sur le mécanisme de croissance de nano-cristaux de cobalt en solution qui ont révélées une influence inattendue de la procédure de préparation de la solution mère sur la morphologie des nanocristaux. En plus,l’utilisation des germes nanoscopiques pour la croissance de Co et de Fe a rendu des nanofils longs de Co et des altères de Co-Fe et elle a contribué à la définition et l’amélioration des conditions expérimentales pour la croissance par germes de Co et de Fe sur les substrats solides. / This thesis concerns a new wet chemical seeded growth method that can produce arrays of metal nanostructures epitaxially grown on crystalline macroscopic surfaces which act as seeds. This approach produces wafer-scale organized 2D hexagonal arrays of perpendicularly oriented, monodisperse and monocrystalline metallic Co nanowires with diameters below 10 nm which exhibit perpendicular magnetic anisotropy and are interesting for applications in ultra high density magnetic recording. Extension of this approach to iron gives rise to nanostructured iron films. The orientation of the nanostructures on the solid substrate depends on the substrate crystallographic orientation, whereas their morphology is dictated by the solution composition. This objective was attained through parallel studies on the growth mechanism of cobalt nano-crystals in solution which revealed an unexpected influence of the stock solution preparation procedure on the nanocrystal morphology. In addition, the use of nanoscopicseeds for the overgrowth of cobalt and iron gave rise to long Co nanowires and Co-Fe dumbbells and contributed to the definition and the improvement of the experimental conditions for the seeded growth of Co and Fe on the solid substrates