4H-SiC-based bipolar junction transistors (BJTs) are attractive devices for high-voltage and high-temperature operations due to their high current capability, low specific on-resistance, and process simplicity. To extend the potential of SiC BJTs to power electronic industrial applications, it is essential to realize high-efficient devices with high-current and low-loss by a reliable and wafer-scale fabrication process. In this thesis, we focus on the improvement of the 4H-SiC BJT performance, including the device optimization and process development. To optimize the 4H-SiC BJT design, a comprehensive study in terms of cell geometries, device scaling, and device layout is performed. The hexagon-cell geometry shows 42% higher current density and 21% lower specific on-resistance at a given maximum current gain compared to the interdigitated finger design. Also, a layout design, called intertwined, is used for 100% usage of the conducting area. A higher current is achieved by saving the inactive portion of the conducting area. Different multi-step etched edge termination techniques with an efficiency of &gt;92% are realized. Regarding the process development, an improved surface passivation is used to reduce the surface recombination and improve the maximum current gain of 4H-SiC BJTs. Moreover, wafer-scale lift-off-free processes for the n- and p-Ohmic contact technologies to 4H-SiC are successfully developed. Both Ohmic metal technologies are based on a self-aligned Ni-silicide (Ni-SALICIDE) process. Regarding the device characterization, a maximum current gain of 40, a specific on-resistance of 20 mΩ·cm2, and a maximum breakdown voltage of 5.85 kV for the 4H-SiC BJTs are measured. By employing the enhanced surface passivation, a maximum current gain of 139 and a specific on-resistance of 579 mΩ·cm2 at the current density of 89 A/cm2 for the 15-kV class BJTs are obtained. Moreover, low-voltage 4H-SiC lateral BJTs and Darlington pair with output current of 1−15 A for high-temperature operations up to 500 °C were fabricated. This thesis focuses on the improvement of the 4H-SiC BJT performance in terms of the device optimization and process development for high-voltage and high-temperature applications. The epilayer design and the device structure and topology are optimized to realize high-efficient BJTs. Also, wafer-scale fabrication process steps are developed to enable realization of high-current devices for the real applications. / <p>QC 20170810</p>

This paper reports a novel and remarkably facile approach towards vertically aligned nanosheets on three-dimensional (3D) Ni foams. Conducting polypyrrole (PPy) sheets were grown on Ni foam through the volatilization of the environmentally friendly solvent from an ethanol–water solution of pyrrole (Py), followed by the polymerization of the coated Py in ammonium persulfate (APS) solution. The PPy-decorated Ni foams and commercial activated carbon (AC) modified Ni foams were employed as the two electrodes for the assembly of flexible all-solid-state asymmetric supercapacitors. The sheet-like structure of PPy and the macroporous feature of the Ni foam, which render large electrode–electrolyte interfaces, resulted in good capacitive performance of the supercapacitors. Moreover, a high energy density of ca. 14 Wh kg−1 and a high power density of 6.2 kW kg−1 were achieved for the all-solid-state asymmetric supercapacitors due to the wide cell voltage window.

This paper reports a novel and remarkably facile approach towards vertically aligned nanosheets on three-dimensional (3D) Ni foams. Conducting polypyrrole (PPy) sheets were grown on Ni foam through the volatilization of the environmentally friendly solvent from an ethanol–water solution of pyrrole (Py), followed by the polymerization of the coated Py in ammonium persulfate (APS) solution. The PPy-decorated Ni foams and commercial activated carbon (AC) modified Ni foams were employed as the two electrodes for the assembly of flexible all-solid-state asymmetric supercapacitors. The sheet-like structure of PPy and the macroporous feature of the Ni foam, which render large electrode–electrolyte interfaces, resulted in good capacitive performance of the supercapacitors. Moreover, a high energy density of ca. 14 Wh kg−1 and a high power density of 6.2 kW kg−1 were achieved for the all-solid-state asymmetric supercapacitors due to the wide cell voltage window.

Les travaux de cette thèse ont porté sur l'élaboration, l'optimisation et l'étude d'électrodes composites de nanotubes de carbone verticalement alignés (VACNT) sur un collecteur d'aluminium et modifiés par l'oxyde de manganèse (MnO₂). Les VACNT synthétisés par voir CVD à basse température (580°C:) directement sur le collecteur ont permis d'obtenir des tapis de NTC parfaitement alignés d'une épaisseur allant de 20 à 80 µm et possédant des densités de 10¹¹ NTC.cm² et dont le taux de catalyseur (Fe) est inférieur à 1%. Leur modification par du MnO2 permet d’accroître leur capacité de stockage électrochimique. Afin de réaliser un enrobage optimal des VACNT par le MnO₂, différents précurseurs de l'oxyde ainsi que diverses méthodes(dépôts électrochimiques, chimiques, CVD) ont été utilisées et optimisées. Les composites élaborés ont ensuite été étudiées en tant que matériau d'électrode pour la réalisation de supercondensateurs asymétriques eu milieux aqueux. / This thesis was focused on the development, optimization and study of composite electrodes of vertically aligned carbon nanotubes (VACNT) on an aluminum collector and modified with manganese oxide (MnO₂).VACNT were synthesized by a CVD process at low temperature (580° C) directly on the collector. Perfectly aligned CNT forest with a thickness of 20 to 80 μm were obtained with high densities of 10¹¹ NTC.cm² and whose catalyst (Fe) content is less than 1%. Their modification with MnO₂ increase their electrochemical storage capacity. In order to achiew optimal coating of VACNT by MnO₂, different precursors of the oxide and various methods ( electrochemical, chemical, CVD) were used and optimized. Composites were studied as electrode material for the realization of asymmetric supercapacitors in aqueous media. In addition, structurals, morphologicals and electrochemicals analyzes carried out on the different materials allowed a better understanding of the role of the elaboration's conditions on the properties of the VACNT/MnO₂ composites obtained.

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<p dir="ltr">Metamaterials are artificially engineered nanoscale systems with a three-dimensional repetitive arrangement of certain components, and present exceptional optical properties for applications in nanophotonics, solar cells, plasmonic devices, and more. Self-assembled oxide-metal vertically aligned nanocomposites (VANs), with metallic phase as nanopillars embedded in the matrix oxide, have been recently proposed as a promising candidate for metamaterial applications. However, precise microstructural control and the structure-property relationships in VANs are still in high demand. Thus, by employing multiple approaches for structural design, this dissertation attempts to investigate the mechanisms of nanostructure evolutions and the corresponding optical responses.</p><p dir="ltr">In this dissertation, the precise control over the nanostructures has been demonstrated through morphology tuning, nanopillar orderings, and strain engineering. Firstly, Au, a well-known plasmonic mediator, has been selected as the metallic phase that forms nanopillars. Based on the previously proposed strain compensation model which describes the basic formation mechanism of VAN morphology, two oxides were then considered: La_0.7Sr_0.3MnO₃(LSMO) and CeO₂. In the first two chapters of this dissertation, LSMO was considered due to its similar lattice (a_LSMO= 3.87 Å, a_Au= 4.08 Å) and its enormous potential in nanoelectronics and spintronics. Deposited on SrTiO₃ (001) substrate through pulsed laser deposition (PLD), LSMO-Au nanocomposites exhibit ideal VAN morphology as well as promising hyperbolic dispersions in response to the incident illuminations. By substrate surface treatment of annealing at 1000°C, and variation of STO substate orientations from (001), to (111) and (110), the improved and tunable in-plan orderings of Au nanopillars have been successfully achieved. In the third chapter, a new oxide-metal VAN system of <a href="" target="_blank">CeO₂</a>-Au (a_CeO2= 5.411 Å, and a_CeO2/= 3.83 Å) has been deposited. The intriguing 45° rotated in-plan epitaxy presents an unexpected update to the strain compensation model, and tuning of Au morphology from nanopillars, nanoantennas, to nanoparticles also shows an effective modulation of the LSPR responses. COMSOL simulations have been exploited to reveal the relationships between Au morphologies and optical responses. In the last chapter, the two VAN systems of LSMO-Au and CeO₂-Au have been combined to form a complex layered VAN thin film. Investigations into the strain states, the nature of complex interfaces, and the according hybrid properties, show dramatic possibilities for further strain engineering. In summary, this dissertation has provided multiple routes for highly tailorable oxide-metal nanocomposite designs. And the two proposed material systems present great potential in optical metamaterial applications including biosensors, photovoltaics, super lenses, and more.</p>

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Idag finns det omkring 5 000 operativa satelliter i omloppsbana runt jorden. Bland dessa finns MATS, DMSP-17/18 och Swarm-A/B/C. De tre satellitprogrammen ger olika data från jordens övre atmosfär där MATS bland annat observerar infraröd emission, DMSP mäter elektron- och jonnedfall från rymden och Swarm bland annat mäter variationer i jordens geomagnetiska fält. Dessa data ger möjlighet att analysera aurora. Aurora, även känt som polarsken, är ett fantastiskt ljusfenomen som kan urskiljas i olika färger och som har forskats på under flera decennier. Till följd av detta finns även möjligheten att göra gymnasieelever mer intresserade av rymden. När elever deltar i autentiskt lärande kan det bidra till ökat intresse inom naturvetenskap. Studien syftar till att undersöka auroraregionerna och jämföra data mellan MATS, DMSP och Swarm för att skapa en helhetsbild av fenomenet. Dessutom utvecklas ett lektionsmaterial som syftar till att öka intresset för rymden och fysik i allmänhet bland gymnasieelever. Metoden för den tekniska delen innefattade att finna konjunktioner mellan MATS och en annan satellit eftersom satelliterna ska ge data för samma fenomen. Under en konjunktion behövde banorna stämma överens samtidigt som satelliterna skulle ha tillgänglig data vid tidpunkten. För den pedagogiska delen har en enkätstudie använts för att samla in lärares åsikter om utveckling och utvärdering av lektionsmaterialet. Fem konjunktioner undersöktes och resultaten visade på en ökning av elektron och jonenergi samt flöde i auroraregioner. Ett fall visade en svag uppåtriktad ström som en potentiell förklaring till den ökade energin, vilket möjligtvis tillåter elektronerna att accelerera mot jorden och därav ökar flödet. Enkätstudien visade att det fanns ett intresse för ett lektionsmaterial. Fokus skulle ligga på att skapa ett autentiskt material där eleverna fick en genomgång om hur polarsken uppstår och därefter diskutera frågor kopplade till materialet. Utvärderingen visade att syftet och lärandemålen för lektionen hade uppfyllts. Eleverna deltog aktivt i diskussioner, ställde följdfrågor och ansågs vara intresserade av materialet. / Today there are around 5 000 operative satellites currently in orbit. MATS,DMSP-17/18 and Swarm-A/B/C are just a few among them. These three satellite programs produce different data from Earth’s upper atmosphere. MATS observe infrared emission, DMSP measure electron- and ion precipitation and Swarm measure variations in Earth’s geomagnetic field. This data provides the opportunity to analyze aurora. Aurora, also known as polar lights, is a fantasticlight phenomenon that can be observed in different colors and has been researched for decades. As a result, there is also a possibility to increase the interest among high school students to learn about space. A contribution to their interest can be seen when the students are allowed to participate in authentic learning.The study aimed to investigate aurora regions and compare data between MATS, DMSP and Swarm in order to create a comprehensive picture of the phenomenon. Additionally, an educational material was developed with the aim of increasing interest in space and physics in general among high school students. The methodology for the technical part consisted of finding conjunctions between MATS and one other satellite. This was because of the fact that the satellites were required to give data from the same phenomenon. During a conjunction the orbits of the satellites had to correspond and the satellites also needed to have available data from the time period. A survey study was conducted for the pedagogical part in order to collect opinions from teachers about the development and evaluation of the educational material. Five conjunctions were examined, and the results indicated an increase in electron and ion energy as well as flux in auroral regions. One case showed a weak upward current as a potential explanation for the increase in energy, possibly allowing electrons to accelerate towards the Earth and thus increasing the flux. The survey study showed that there was an interest in the educational material. The focus would be to create an authentic material where students were given an overview of how aurora occur followed by questions to discuss related to the material. The evaluation showed that the purpose and learning objectives of the lesson had been fulfilled. Students actively participated in discussions, asked follow-up questions and were considered to be interested in the material.

Les travaux réalisés dans le cadre de cette thèse ont porté sur la réalisation de matériaux composites nanostructurés à base de nanotubes de carbone verticalement alignés (NTC alignés) et de polymères π-conjugués en vue de leur utilisation en tant que matériaux d’électrodes dans des dispositifs de stockage d’énergie de type supercondensateurs. Dans une première partie, les travaux se sont focalisés sur la croissance par CVD d’aérosol de NTC sur des substrats d’acier inoxydable via le dépôt préalable d’une sous-couche céramique SiOx. Grâce à l’optimisation de ce procédé, des tapis de NTC longs, denses et alignés pouvant directement servir de supports à l’électrodépôt de polymères π-conjugués ont pu être obtenus. Dans une seconde partie, les travaux se sont concentrés sur l’électrodépôt de poly(3-méthylthiophène) (P3MT) en milieu liquide ionique EMITFSI sur les tapis de NTC alignés à partir d’une méthode chronopotentiométrique « séquencée » permettant de réaliser des dépôts homogènes dans la profondeur des tapis. Une composition massique optimale de 70 % de P3MT permettant d’atteindre des capacitances spécifiques de 170 F.g-1 de polymère tout en conservant des cinétiques de charge-décharges élevées, comparativement à des composites NTC/P3MT enchevêtrés, a pu être déterminée. A partir des matériaux composites optimisés, des dispositifs symétriques NTC/P3MT // P3MT/NTC et hybrides CA // P3MT/NTC ont été assemblés. Le dispositif hybride à notamment permis d’atteindre une tension de 2,7 V et une capacitance de système de 26 F.g-1 en milieu EMITFSI à 25 °C. Par ailleurs, une énergie maximale de 23 Wh.kg-1 et une puissance maximale de 6,9 kW.kg-1 ont été obtenues avec une perte de seulement 7 % après 4000 cycles. Pour finir, l’électrodépôt de polypyrrole (Ppy) a été étudié dans différents milieux liquides ioniques protiques et aprotiques. Après des études réalisées par microbalance à cristal de quartz permettant de mieux comprendre les mécanismes d’insertion des espèces ioniques lors de la croissance du polymère conjugué et lors de son dopage positif réversible, des dépôt de Ppy ont été réalisés et optimisés dans la profondeur des tapis de NTC alignés. Des nanocomposites NTC alignés/Ppy présentant des capacitances spécifiques comprises entre 100 et 130 F.g-1 ont ainsi pu être obtenus. / This thesis focused on the elaboration of nanostructured composite materials based on vertically aligned carbon nanotubes (aligned CNT) and π-conjugated polymers and their use as electrode materials in supercapacitor-type energy storage devices. The first part focused on aligned CNT growth by aerosol-assisted CVD on stainless steel substrates and the deposition of a SiOx ceramic sublayer. Thanks to the optimization of this growth process, long, dense, and aligned CNT carpets which can directly act as support for the electrodeposition of π-conjugated polymers were obtained. The second part focused on the electrodeposition of poly (3-methylthiophene) (P3MT) in EMITFSI ionic liquid medium on aligned CNT carpets using a “pulsed” chronopotentiometric method to produce homogeneous deposits in the depth of the carpets. An optimal P3MT mass composition of 70 %, which helped achieve a specific capacitance of 170 F.g-1 of polymer while maintaining high charge-discharge kinetics, compared with NTC/P3MT entangled composites, was determined. NTC/P3MT // P3MT/NTC symmetrical devices and CA // P3MT/NTC hybrid devices were assembled using the optimized composite materials. The hybrid device reached a voltage of 2.7 V and a system capacitance of 26 F.g-1 in EMITFSI at 25 ° C. Furthermore, a maximum energy of 23 Wh.kg-1 and a maximum power of 6.9 kW.kg-1 were obtained with only a 7 % loss after 4000 cycles. Finally, the electrodeposition of polypyrrole (Ppy) was investigated in different protic and aprotic ionic liquids. After quartz crystal microbalance studies in order to better understand the insertion mechanisms of ionic species during conjugated polymer growth and during its reversible positive doping, the electrodeposition of Ppy within the deepness of the aligned CNT carpets was optimized. Aligned CNT/Ppy nanocomposites with specific capacitances ranging between 100 and 130 F.g-1 were obtained.