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1
Gadea, Gerard. "Integration of Si/Si-Ge nanostructures in micro-thermoelectric generators." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/459243.
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Silicon and silicon-germanium nanostructures were grown, integrated, optimized and characterized for their application in thermoelectric generation. Specifically two kinds of nanostructures were worked: silicon and silicon-germanium nanowire arrays (Si/Si-Ge NW) and polycrystalline silicon nanotube fabrics (pSi NT).
The results are dived in four chapters. Chapters 3, 4 and 5 deal with Si/Si-Ge NWs, while chapter 6 presents the pSi NT fabrics.
In Chapter 3 the growth and integration of Si/Si-Ge NWs was studied, in order to optimize their properties for thermoelectric application in micro-thermoelectric generators (µTEG). First, the methods for depositing gold nanoparticles prior to NW growth were studied. Second, the growth of NWs from the gold nanoparticles in a Chemical Vapour Deposition (CVD) process was comprehensively studied and optimized for subsequent integration of NWs in µTEGs, both of Si and Si-Ge. All important properties – NW length, diameter, density, doping and alignment
– could be controlled by tuning the seeding gold nanoparticles and the process conditions, namely temperature, pressure, flows of reactants and growth time. Finally, integration was demonstrated in micro-structures for thermoelectric generation and characterization. The optimization process yielded to fully integrated thermoelectric Si/Si-Ge NW arrays with diameters and densities of ~100 nm and 5 NW/µm2 respectively.
In Chapter 4 the Si NWs were thermoelectrically characterized. The Seebeck coefficient, electrical conductivity and thermal conductivity of arrays and single Si-NWs were measured in microstructures devoted to characterization comprising NWs integrated as in final µTEG application. Additionally a novel atomic force microscope based method for determination of thermal conductivity was explored. Then the results were discussed comparing them with existing literature. A ZT of 0.022 was found at room temperature, revealing an improvement of factor 2-3 with respect to bulk.
In Chapter 5 The harvesting capabilities of µTEGs with integrated Si/Si-Ge NWs was assessed. The thermal gradient and the power of the µTEGs was assessed for two generation of devices and for two thermoelectric materials, namely Si and Si-Ge NWs, which were integrated for the first time in functional generators. Also a study on heat sinking and convection effects was conducted adding insight towards further device improvement. Finally, the results were discussed and compared with literature. The maximum power densities attained were 4.5
µW/cm2 for the Si NWs and 4.9 µW/cm2 for the Si-Ge NWs while harvesting over surfaces at
350 ºC.
Chapter 6 deals with pSi NT fibers. First this new material concept and the growth route are presented, showing the fabrication steps and the control of the resulting properties by CVD method. Then the material is thermoelectrically characterized, by measuring its Seebeck coefficient and electrical and thermal conductivities up to 450 ºC. A ZT of 0.12 was found, doubling the optimally doped bulk at this temperature. Finally a proof of concept was demonstrated by assessing the thermal harvesting capabilities of the material on top of hot surfaces. A maximum of 3.5 mW/cm2 was attained at 650 ºC.Los materiales termoeléctricos permiten la conversión de calor a electricidad y viceversa. Esto permite explotar el efecto termoeléctrico en generadores termoeléctricos, capaces de extraer energía térmica de fuentes calientes y convertirla a electricidad útil. Estos generadores presentan grandes ventajas, como su falta de piezas móviles – y por ende necesidad de mantenimiento alguna – y su total escalabilidad, que permite cambiar su tamaño sin afectar su rendimiento. Esto los hace obvios candidatos para la alimentación y carga de dispositivos portátiles y situados lugares de difícil acceso. A pesar de ello, su uso no está muy extendido debido a que su relación eficiencia-coste es baja en comparación a otros métodos capaces de suplir las funciones de alimentación – como la sustitución periódica de baterías – o de conversión térmica-eléctrica – como las turbinas de vapor. Los materiales termoeléctricos suelen ser o eficientes y caros (como el Bi2Te3 usado en los módulos comerciales) o ineficientes y de bajo coste (como el silicio, barato por su abundancia ya que supone un 28% de la corteza terrestre). En este trabajo se han crecido nanostructuras de silicio y silicio-germano, con dimensiones en el orden de los 100 nm. Los nanomateriales presentan propiedades termoeléctricas mejoradas respecto a sus contrapartes macroscópicas. Gracias a la nanoestructuración pues, se ha abordado del problema de eficiencia-coste por dos vertientes: • En el caso del silicio – normalmente un mal termoeléctrico debido a su alta conductividad térmica – se ha habilitado su uso como termoeléctrico al crecerlo en forma de nanohilos cristalinos y nanotubos de silicio policristalino. • En el caso de silicio-germano – que ya es un buen termoeléctrico para uso en altas temperaturas – se ha aumentado su eficiencia aún más, creciéndolo en forma de nanohilos. Yendo más allá de la síntesis, los nanohilos de silicio/silicio-germano se han optimizado, caracterizado en integrado en gran número micro-generadores termoeléctricos de 1 mm2 de superficie, pensados para la alimentación de pequeños dispositivos y circuitos integrados. Respecto a los nanotubos de Si, estos se han obtenido en densas fibras macroscópicas aptas para su aplicación directa como generadores termoeléctricos de gran área. Cabe mencionar que ambos nanomateriales – así como los microgeneradores basados en nanohilos – fueron obtenidos mediante técnicas actualmente utilizadas para la fabricación de circuitos integrados, pensando en la escalabilidad del proceso para su aplicación. El trabajo presentado en esta tesis consiste en el crecimiento, optimización, estudio e integración de nanostructuras de Si/Si-Ge para su aplicación en generación termoeléctrica. En los Capítulos 1 y 2 se pone un marco a los materiales tratados y su aplicación y se describen los métodos utilizados, respectivamente. Los resultados se han dividido en cuatro capítulos. En los Capítulos 3, 4 y 5 se tratan los nanohilos abordando su crecimiento, caracterización y aplicación en microgeneradores, respectivamente. En el Capítulo 6 se tratan las fibras de nanotubos, integrando todo el estudio en el mismo capítulo. Finalmente en el Capítulo 7 se muestran las conclusiones, resumiendo los resultados e indicando la relevancia del trabajo.
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Elfving, Anders. "Near-infrared photodetectors based on Si/SiGe nanostructures." Doctoral thesis, Linköping : Surface and Semiconductor Physics, Linköping University, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-5909.
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Pascale, Alina Mihaela. "Evolution morphologique des nanostructures Si(1-x)Ge(x) pendant la croissance par EJM." Aix-Marseille 2, 2003. https://tel.archives-ouvertes.fr/tel-00504903.
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Dans ce travail nous avons étudié l'auto-organisation d'îlots de Ge sur des substrats vicinaux de Si nanostructurés en utilisant un processus à deux étapes qui consiste en :1) l'auto-structuration naturelle du substrat et 2) la nucléation préférentielle des îlots de Ge sur les motifs créés. Après des rappels bibliographiques dans les trois premiers chapitres, nous présentons les résultats, à la fois théoriques et expérimentaux, dans les deux derniers chapitres. En particulier, nous avons mis en évidence : a) une pseudo-barrière Ehrlich-Schwoebel inverse implicite à l'origine de l'instabilité cinétique qui se développe durant l'homoépitaxie Si/Si(001), avec des exposants critiques en bon accord avec la théorie et b) une réduction importante de l'énergie élastique d'un système comprenant un îlot de Ge, une couche de mouillage de Ge et un substrat à motifs de Si (où chaque motif est représenté par des marches) lorsque le motif possède au moins trois marchesIn this work we studied the Ge dots self-organization on vicinal Si substrates nanostructured by using a two stages process which consists of: i) substrate natural self-structuration and ii) Ge dots preferential nucleation on the created patterns. After bibliographical recalls in the first three chapters, we present the theoretical and experimental results in the two last chapters. In particular, we have evidenced: a) an implicit inverse Ehrlich-Schwoebel pseudo-barrier at the origin of the kinetic instability which develops during the homoepitaxial growth Si/Si(001), with scaling exponents in good agreement with the theory and b) an important reduction of the elastic energy of a system including a Ge dot, a Ge wetting layer and a Si patterned substrate (where each pattern is represented by steps) when the pattern is constitued of three steps at least
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Portavoce, Alain. "Mécanismes élémentaires de redistribution de l'antimoine au cours de la croissance d'hétérostructure Si/Si(1-x)Ge(x) : Diffusion, ségrégation, désorption et effet surfactant." Aix-Marseille 3, 2002. http://www.theses.fr/2002AIX30060.
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Les nouvelles structures micro et nano-électroniques à base SiGe imposent un contrôle rigoureux du dopage et pour certaines un confinement 3D. Nous avons analysé les phénomènes de redistribution de dopants (B, Sb) pendant la croissance par MBE de couches SiGe en épitaxie sur Si: diffusion, ségrégation, désorption, effet surfactant. Notre approche (couches sous divers états de contrainte) permet de séparer l'effet de la teneur en Ge de celui de la contrainte. La diffusion du Sb augmente avec la teneur en Ge et avec une compression biaxiale, celle du B suit le comportement inverse. Nous montrons que ces variations sont en accord avec un mécanisme principalement lacunaire pour le Sb et interstitiel pour le B. La ségrégation en cours de croissance varie de façon identique à la diffusion, montrant la prédominance de la cinétique. Le contrôle de la concentration superficielle de Sb permet de faire croître des couches de Ge planes ou de réduire la taille et d'augmenter la densité des îlots de GeThe future SiGe structures for micro and nano-electronic impose a strict doping control and for some of them a 3D confinement. We have analysed the dopant (B, Sb) redistribution phenomena during the MBE growth of SiGe layers in epitaxy on Si: diffusion, segregation, desorption, surfactant effect. Our approach (layers under various states of stress) permits to separate the Ge concentration effect from the strain effect. Sb diffusion increases with Ge concentration and with biaxial compression, while the B diffusion follows the opposite behaviour. We show that these variations are in agreement with a mechanism using principally vacancies for Sb and interstitials for B. Surface segregation during growth follows the same variations as diffusion, showing the prevalence of kinetics. The control of the superficial Sb coverage allows either the growth of thicker flat Ge layers or to reduce the size and to increase the density of Ge islands
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Moontragoon, Pairot. "Band structure calculation of Si-Ge-Sn binary and ternary alloys, nanostructures and devices." Thesis, University of Leeds, 2009. http://etheses.whiterose.ac.uk/5850/.
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Alloys of silicon (Si), germanium (Ge) and tin (Sn) are continuously attracting research attention as possible direct band gap semiconductors with prospective applications in optoelectronics. The direct gap property may be brought about by the alloy composition alone or combined with the influence of strain, when an alloy layer is grown on a virtual substrate of different composition. Si-GeSn nanostructures are also promising materials because they are compatible with Si-based technology, and have a high potential in many optoelectronic applications, such as silicon-based Ge/SiGeSn band-to-band and inter-subband lasers. In search for direct gap materials, the electronic structure of relaxed or strained Gel-xSnx and Si1-xSnx alloys, and of strained Ge grown on relaxed Gel_x_ySixSny, were calculated by the self-consistent pseudo-potential plane wave method, within the mixed-atom supercell model of alloys, which was found to offer a much better accuracy than the virtual crystal approximation. Expressions are given for the direct and indirect band gaps in relaxed Gel-xSnx, strained Ge grown on relaxed SixGel-x_ySny, and for strained Gel-xSnx grown on a relaxed Gel_ySny substrate, and these constitute the criteria for achieving a direct band gap semiconductor, by using appropriate tensile strain. In particular, strained Ge on relaxed SixGel_x_ySny has a direct gap for y > 0.12 + 0.20x, while strained Gel-xSnx on relaxed Gel_ySny has a direct gap for y > 3.2x2 - 0.07x + 0.09. In contrast, within the mixed-atom approach the SnxSi1- x alloys never show a finite direct band gap (while the VCA calculation does predict it). Self-assembled quantum dots in Si-Ge-Sn system attract research attention as possible direct band gap materials, compatible with Si-based technology, with potential applications in optoelectronics. In this work, the electronic structure near the f-point and interband optical matrix elements of strained Sn and SnGe quantum dots in Si or Ge matrix are calculated using the eightband k· p method, and the competing L-valley conduction band states were found by the effective mass method. The strain distribution in the dots was found with the continuum mechanical model. The parameters required for the k· p or effective mass calculation for Sn were extracted by fitting to the energy band structure calculated by the nonlocal empirical pseudopotential method (EPM). The calculations show that the self-assembled Sn/Si dots, sized between 4 nm and 12 nm, have indirect interband transition energies between 0.8 to 0.4 eV and direct interband transitions between 2.5 to 2.0 eV. In particular, the actually grown, approximately cylindrical Sn dots in Si with a diameter and height of about 5 nm are calculated to have an indirect transition (to the L valley) of about 0.7 eV, which agrees very well with experimental results. Similar good agreement with experiment was also found for SnGe dots grown on Si. However, neither of these are predicted to be direct band gap materials, in contrast to some earlier expectations. In order to extend a creativity in developing a complete suite of Si-base optoelectronic devices, SiGeSn alloys are considered as promising materials for optoelectronic applications because they offer the possibility for a direct band gap and are compatible with Si-based technology, therefore having a perspective of applications for interband lasers and detectors, solar cells, etc. In this work, another possible application of nanostructures based on these materials was considered: to extend the suite of Si-based optoelectronic devices, namely for interband electro-absorption modulators. Using the 8-band k.p method asymmetric double quantum wells have been designed and optimized, by varying the well and barrier widths and material composition, to show large optical transmission sensitivity to the applied bias. Generally, these structures are useful for electro-absorption modulators in the mid-infrared spectral range.
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Ruh, Elisabeth Margrit. "Investigation of the local Ge concentration in Si/SiGe nanostructures by convergent-beam electron diffraction /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17908.
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Bohorquez, Ballen Jaime. "Thermal transport in low dimensional semiconductor nanostructures." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/dissertations/798.
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We have performed a first principles density functional theory (DFT) calculations to study the thermal conductivity in ZnO nanotubes, ZnO nanowires, and Si/Ge shell-core nanowires. We found the equilibrium configuration and the electric band structure of each nanostructure using DFT, the interatomic force constants and the phonon dispersion relations were calculated using DFPT as implemented in Quantum Espresso. In order to fundamentally understand the effect of atomic arrangements, we calculated the phonon conductance in a ballistic approach using a Green's function method. All ZnO nanostructures studied exhibit semiconducting behavior, with direct bandgap at the Gamma point. The calculated values for the bandgaps were larger than the value of the bandgap of the bulk ZnO. We were able to identify phonon modes in which the motion of Zn atoms is significant when it is compared with the motion of oxygen atoms. The thermal conductivity depends on the diameter of the nanowires and nanotubes and it is dramatically affected when the nanowire or nanotube is doped with Ga. For Si/Ge nanowires, the slope and the curvature of acoustic modes in the phonon dispersion relation increases when the diameter increases. For nanowires with the same number of atoms, the slope and curvature of acoustic modes depends on the concentration of Si atoms. We were able to identify phonon modes in which the motion of core atoms is significant when it is compared with motion of atoms on the nanowire's shell. The thermal conductivity in these nanostructures depends on the nanowire's diameter and on the Si atoms concentration.
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Kozlowski, Grzegorz [Verfasser], and Thomas [Akademischer Betreuer] Schröder. "On the compliant behaviour of free-standing Si nanostructures on Si(001) for Ge nanoheteroepitaxy / Grzegorz Kozlowski. Betreuer: Thomas Schröder." Cottbus : Universitätsbibliothek der BTU Cottbus, 2012. http://d-nb.info/1022561456/34.
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Cariou, Romain. "Epitaxial growth of Si(Ge) materials on Si and GaAs by low temperature PECVD: towards tandem devices." Palaiseau, Ecole polytechnique, 2014. https://theses.hal.science/tel-01113794/document.
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Cette thèse s'intéresse à la croissance épitaxiale de Si et SiGe à basse température (200°C) par dépôt chimique en phase vapeur assistée par plasma (PECVD), et à l'utilisation de ces matériaux cristallins dans les cellules solaires en couches minces. L'objectif était de mieux comprendre cette croissance inattendue et d'étudier le potentiel de ces matériaux pour les cellules simples et multijonctions. Nous avons d'abord démontré qu'il est possible d'effectuer, avec un réacteur PECVD standard, un nettoyage efficace de la surface du c-Si et de poursuivre par une croissance épitaxiale de couches de Si jusqu'à 8µm d'épaisseur. L'impact des paramètres du procédé tels que la dilution du SiH4 dans l'H2, l'énergie des ions ou encore la pression totale, sur la qualité des couches a été mis en évidence. Les propriétés électriques et structurelles des couches ont été analysées, et nous avons démontré une amélioration de la qualité cristalline avec l'épaisseur de la couche. La croissance épitaxiale de Ge et SiGe sur c-Si dans des conditions similaires a également été établie. Ensuite, par une séquence d'étapes à moins de 200°C, des hétérojonctions PIN sur substrats très dopés, avec une couche absorbante épitaxiée de 1-4µm ont été réalisées, atteignant 8. 8% de rendement (sans piégeage optique) et 80% de FF. Le remplacement du Si par du Si0:73Ge0:27 a permis un gain de 11% sur le Jsc. Le contrôle de l'interface wafer/épi et des contraintes permet de favoriser le décollement : des couches epi-Si de 1. 5µm/10cm^2 ont été reportées sur verre avec succés. Nous avons également analysé l'influence de nanostructures photoniques sur les propriétés des dispositifs. L'étude conjointe de la croissance, du transfert et du piégeage optique ouvre la voie aux cellules c-Si ultra-minces (<10µm) bas côut. Enffin, contrairement au scénario classique de dépôt des matériaux III-V sur Si, nous avons étudié l'hétéroépitaxie de Si sur III-V. Avec cette approche, une bonne qualité cristalline de Si déposé directement sur GaAs est obtenue grâce aux faibles contraintes thermiques et à l'absence de problèmes de polarité à l'interface. Nous avons fabriqué des cellules GaAs avec 20% d'efficacité et des jonctions tunnel atteignant 55A/cm^2 par dépôt MOVPE. Une augmentation du courant tunnel par exposition au plasma d'hydrogène a aussi été démontrée. Ces résultats de croissance, cellule et jonction tunnel, couplés aux techniques de report, valident les briques élémentaires pour atteindre une cellule tandem AlGaAs(MOVPE)/SiGe(PECVD) à haut rendementThis thesis focuses on epitaxial growth of Si and SiGe at low temperature (200°C) by Plasma Enhanced Chemical Vapor Deposition (PECVD), and its application in thin film crystalline solar cells. Our goal is to gain insight into this unusual growth process, as well as to investigate the potential of such low temperaturedeposited material for single and multi-junction solar cells. First, we have proposed a one pump-down plasma process to clean out-of-the-box c-Si wafer surface and grow epitaxial layers of up to 8µm thick, without ultra-high vacuum, in a standard RF-PECVD reactor. By exploring the experimental parameters space, the link between layer quality and important physical variables, such as silane dilution, ion energy, or deposition pressure, has been confirmed. Both material and electrical properties were analyzed, and we found that epitaxial quality improves with film thickness. Furthermore, we could bring evidence of SiGe and Ge epitaxial growth under similar conditions. Then, with the whole process steps <200°C, we have achieved PIN heterojunction solar cells on highly doped substrates with 1-4µm epitaxial absorber, reaching 8. 8% efficiency (without light trapping) and 80. 5% FF. Replacing Si absorber by epitaxial Si0:73Ge0:27 resulted in 11% boost in Jsc. The use of an engineered wafer/epitaxial layer interface and stress enables easy lift-off: e. G. We successfully bonded 1. 5µm thick 10cm^2 epi-Si to glass. Additionally, we have considered the impact of photonic nanostructures on device properties. Together, the control of growth, transfer and advanced light trapping are paving the way toward highly efficient, ultrathin (<10µm) and low cost c-Si cells. Finally, in contrast with general trend of growing III-V semiconductors on Si, we have studied the hetero-epitaxial growth of Si on III-V. Good crystal quality was achieved by direct Si deposition on GaAs, thanks to reduced thermal load and suppressed polarity issues in this approach. Using MOCVD, we could build GaAs cells with 20% efficiency and III-V tunnel junctions reaching 55A/cm^2. Tunneling improvement upon H-plasma exposure was shown. Those results, combined with III-V layer lift-off, validate milestones toward high efficiency tandem AlGaAs(MOVD)/SiGe(PECVD) metamorphic solar cells
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Lin, Zhen. "AFM electrical mode development for nanostructure semiconductor study : application on Ge / Si nanostructure." Lyon, INSA, 2010. http://theses.insa-lyon.fr/publication/2010ISAL0135/these.pdf.
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Aujourd'hui, la technologie des semi-conducteurs est confrontée au défi de la réduction ultime de la taille des composants pour augmenter la performance des appareillages électroniques en les miniaturisant. Cette forte réduction d'échelle provoque un développement considérable des techniques de microscopie pour révéler de nouvelles caractéristiques physiques à l'échelle nanométrique. La compréhension de ces nouvelles propriétés à l'échelle du nanomètre est donc de première importance. Dans ce travail, l’utilisation et l’application des techniques de caractérisation des propriétés électriques par microscopie à force atomique à pointes conductrices sont développées vis-à-vis de l’application aux semi-conducteurs. Les modes électriques spécifiques, comprenant la mesure de capacité par microscopie AFM (SCM) et la spectroscopie associée (SCS), la microscopie à force électrostatique (EFM) et la microscopie à sonde locale de Kelvin (KPFM) sont utilisées à température ambiante pour étudier les propriétés électroniques de nanostructures de germanium sur silicium qui ont été fabriquées par un procédé de démouillage. Il ressort que les mesures SCM, SCS, EFM et KPFM sont bien adaptées pour la caractérisation de nanostructures semi-conductrices, en particulier pour l'étude des nanocristaux à l'échelle du nanomètre. Ces travaux de caractérisation par AFM à modes électriques sont d'une importance primordiale dans le développement de dispositifs électroniques, en particulier pour l'application de transistors à mémoire utilisant des nanoilots de Ge / SiNowadays, the semiconductor technology is facing a great challenge to increase the device performance while reducing its dimension. This downscaling in microelectronics industry causes a drastic development of microscopy to reveal new physical characteristics at nanoscale. The understanding of these new properties in nanometer scale is of prime importance. In this work, the AFM fundamental working principle and some typical electric property characterization techniques in semiconductor industry were introduced. The electrical AFM modes including scanning capacitance microscopy (SCM) and spectroscopy (SCS), electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM) were developed at room temperature to study the properties of the promising replacement of the conventional poly-silicon floating gate, Germanium nanocrystals local Ge/Si nanostructures, which were fabricated by dewetting process. SCM, SCS, EFM and KPFM were proved to be available methodologies for semiconductor nanostructures characterizations, especially the nanocrystal study in nanometer scale. These characterisation works with developed AFM electrical mode are of prime importance in developing electronic devices application, especially the memory transistors application using Ge/Si nanocrystal
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Khovaylo, V., A. Usenko, M. Gorshenkov, and S. Kaloshkin. "Optimization of Ball-Milling Process for Preparation of Si-Ge Nanostructured Thermoelectric Materials." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35302.
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Here we report on technical details of preparation of Si-Ge-based nanostructured thermoelectic materials
by a mechnical alloying method. It has been shown that for a milling speed of 350 rpm a single Si-Ge
phase is formed after milling time less than 6 h.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35302
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Wang, Xiaowei. "Thermoelectric property studies on nanostructured N-type Si-Ge Bulk Materials." Thesis, Boston College, 2009. http://hdl.handle.net/2345/2504.
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Thesis advisor: Zhifeng RenSiGe alloys are the only proven thermoelectric materials in power generation devices operating above 600 °C and up to 1000 °C in heat conversion into electricity using a radioisotope as the heat source. In addition to radioisotope applications, SiGe thermoelectric materials have many other potential applications, for example, solar thermal to electricity energy conversion and waste heat recovery. However, traditional SiGe alloy material shows low ZT values of about 0.93 at 900 °C, thus, 8% is the highest device efficiency for commercial SiGe thermoelectric devices. Recently, many efforts have been made to enhance the dimensionless thermoelectric figure-of-merit (ZT) of SiGe alloys. Among them, the nano approach has been recognized as an effective mechanism to obtain thermoelectric materials with good performance. In this approach, dense bulk samples with random nanostructures with high interface densities are synthesized through ball milling and a direct current hot press, leading to an enhancement ZT through reduced phonon thermal conductivity. Such a practical technique produced samples of nanostructured p-type dense bulk bismuth antimony telluride with a peak ZT of 1.4 at 1000 °C from either alloy ingot or elemental chunks. However, the generality of this approach has not been demonstrated. Here, we applied the same technique in SiGe system in order to fabricate a nanostructured n-type SiGe alloy with enhanced thermoelectric properties. In this thesis, numerous nanostructured n-type SiGe alloy samples were successfully pressed. The structure of these nanostructured samples was investigated via XRD, EDS, and TEM. It has been confirmed that many nano grains exist in our nanostructured samples
Thesis (PhD) — Boston College, 2009
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Voronin, A. I., A. A. Usenko, A. V. Korotitsky, D. U. Karpenkov, O. N. Maradudina, and V. V. Khovaylo. "Thermoelectric Properties of Si-Ge Nanostructured Thermoelectric Materials Synthesized by Mechanical Alloying." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35515.
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Silicon-germanium alloys is one of the best thermoelectric materials in power generation devices operating
in 600-1000 C range in heat conversion into electricity directly. The enhancement of efficiency comes
mainly from a significant reduction in the thermal conductivity caused by the enhanced phonon scattering
off the increased density of nanograin boundaries.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35515
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Mortada, Hussein. "Croissance et caractérisation de nanostructures de Ge et Si déposées sur des substrats d'oxyde cristallin à forte permittivité LaA1O3." Phd thesis, Université de Haute Alsace - Mulhouse, 2009. http://tel.archives-ouvertes.fr/tel-00584121.
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Les mémoires flash non volatiles - utilisées dans les ordinateurs, téléphones portables ou clés USB - peuvent être constituées de nanocristaux semiconducteurs (SC) insérées dans une matrice isolante. Elles nécessitent l'élaboration d'hétérostructures de type "oxyde/SC/oxyde/Si(00l)" et la maîtrise de chaque interface. Dans ce cadre, nous avons étudié les mécanismes de croissance initiale du Si et du Ge (SC) sur des substrats d'oxyde cristallins LaA1O3(001) à forte permittivité (high-k). Les propriétés chimiques et structurales ont été déterminées in-situ par photoémission X (XPS et XPD) et par diffraction d'électrons (RHEED et LEED) puis ex-situ par microscopies en champ proche (AFM) et en transmission (HRTEM). Le substrat LaAlO3(001) propre présente une reconstruction de surface c(2x2) attribuée à des lacunes d'O en surface. Les croissances de Si et Ge ont été réalisées par épitaxie par jet moléculaire (MBE), soit à température ambiante suivies de recuits, soit à haute température. L'épitaxie requiert des températures de dépôt supérieures à 550°C. Le mode de croissance est de type Volmer Weber caractérisé par la formation d'îlots cristallins de dimensions nanométriques et de forte densité. Ces îlots sont relaxés et présentent une interface abrupte avec le substrat. Quant aux îlots de Ge, ils ont majoritairement des orientations aléatoires avec néanmoins une relation d'épitaxie privilégiée, la même que celle du Si.
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Usenko, A., V. V. Khovaylo, A. I. Voronin, A. V. Korotitsky, D. Yu Karpenkov, and O. N. Maradudina. "Study of Compacting Methods for Nanostructured Thermoelectric Materials Based on Si-Ge and Half -Heusler Alloys." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35514.
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Recent methods of compacting nanopowders of thermoelectric materials of silicon germanium and
Half-Heusler (HH) compounds based on Ni(Ti,Zr,Hf)Sn are presented. Half-Heusler alloys are known to be
intermetallic compounds with quite large Seebeck coefficient and semiconducting transport properties.
This makes them a potential candidate for thermoelectric applications. In this study we compare compacting
methods applied to raw materials as a function of crystal structure. The results suggest that the thermal
conductivity can be reduced by increasing the phonon scattering via nanostructuring. The effect of
spark plasma sintering (SPS) and hot pressing on Gleeble system was analyzed by TEM and SEM methods.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35514
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Dujardin, Romain. "Epitaxie par jets moléculaires de nanostructures isolées de germanium sur silicium." Phd thesis, Université Joseph Fourier (Grenoble), 2006. http://tel.archives-ouvertes.fr/tel-00133594.
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Les travaux présentés dans ce manuscrit sont consacrés à la croissance par épitaxie par jets moléculaires (EJM) de nanostructures isolées de Ge sur Si. Nous nous sommes intéressés à trois types de nanostructures; des boîtes quantiques isoléees de Ge avec une forte densité, des boîtes de Ge auto organisées sur des îlots de Si et des nanostructures de Ge incorporées dans des nanofils de Si. Un effort important a été porté sur l'élaboration de ces nanostructures par la voie EJM et sur la caractérisation de leurs propriétés structurales et chimiques. Nous avons mis en évidence par une étude de diffraction X en incidence rasante (GID) et par spectroscopie d'absorption X (EXAFS) que les boîtes quantiques de Ge épitaxiées à travers une fine couche d'oxyde étaient fortement contraintes par rapport au substrat de Si et sont presque pures Ge. La structure cristalline des boites de Ge encapsulées dans le Si a été étudiée par microscopie électronique en haute résolution (MET) et une étude par photoluminescence à basse température a montré une émission de ces boîtes dans le spectre visible. Cette luminescence a été attribuée à la présence deliaison résiduelle Ge-O à l'interface entre les boîtes et le Si d'encapsulation. La croissance d'îlots de Si par épitaxie latérale à travers la couche d'oxyde a permis de supprimer ces liaisons et d'obtenir une luminescence des boîtes de Ge dans l'infra rouge avec une très faible largeur de raie. Ce phénomène est attribué à une faible dispersion en taille des boites
de Ge élaborées sur ces ilots de Si. Le dernier volet de ces travaux a porté sur l'élaboration de nanofils de Si par la voie VLS et sur l'incorporation de couches fines de Ge dans ces nanofils. L'interdiffusion du silicium dans ces couches de Ge a été quantifié par diffraction anomale et la structure cristalline des fils a été étudiée par MET.
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Garchery, Laurent. "Fabrication et étude des propriétés physiques des nanostructures Si/SiGe : application aux nouveaux dispositifs." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10232.
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La technologie de la microelectronique silicium beneficie aujourd'hui d'investissements massifs et continus. Tout porte a croire que les excellentes proprietes du systeme si/sio#2 assureront la perennite du si pendant encore de nombreuses annees. Le developpement de nouveaux materiaux pouvant ameliorer les performances des dispositifs a base de si est donc encourage. En particulier, l'heterosysteme si/sige apparait comme le meilleur candidat pour le developpement d'une technologie a heterojonction a base de si. De tels materiaux doivent cependant etre compatibles avec les temperatures de recuit utilisees dans la technologie si. Les deux principaux dispositifs electroniques dans lesquels l'utilisation du sige est envisagee sont le transistor bipolaire et le transistor a effet de champ. Dans le cas du transistor a effet de champ, l'interet du sige est d'ameliorer les proprietes de transport parallele au plan des couches. Cette these est consacree a l'etude experimentale de ces proprietes ainsi qu'a l'analyse et a la comprehension du fonctionnement des heteronjonctions si/sige. Nous rappelons tout d'abord les proprietes de structure de bandes des heterosystemes contraints si/sige ainsi que la methode de mesure par effet hall que nous avons utilisee. Une etude de l'evolution thermique des proprietes de transport et de confinement de modulations de dopage si/sige de type p est ensuite presentee. Puis, nous analysons les proprietes de transport electronique des heterostructures si/sige elaborees sur un pseudo-substrat de sige relaxe. Le principe de fonctionnement specifique des dispositifs mos a canal enterre en sige est ensuite mis en evidence experimentalement. Nous constaterons finalement que les caracteristiques electriques des dispositifs mos a base de si peuvent etre ameliorees par l'introduction d'un canal enterre en sige
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Joshi, Giri Raj. "Study of Thermoelectric Properties of Nanostructured P-Type Si-Ge, Bi-Te, Bi-Sb, and Half-Heusler Bulk Materials." Thesis, Boston College, 2010. http://hdl.handle.net/2345/2463.
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Thesis advisor: Zhifeng RenSilicon germanium alloys (SiGe) have long been used in thermoelectric modules for deep-space missions to convert radio-isotope heat into electricity. They also hold promise in terrestrial applications such as waste heat recovery. The performance of these materials depends on the dimensionless figure-of-merit ZT (= S2σ T/ κ), where S is the Seebeck coefficient, σ the electrical conductivity, κ the thermal conductivity, and T is the absolute temperature. Since 1960 efforts have been made to improve the ZT of SiGe alloys, with the peak ZT of n-type SiGe reaching 1 at 900 - 950 C. However, the ZT of p-type SiGe has remained low. Current space-flights run on p-type materials with a peak ZT ~ 0.5 and the best reported p-type material has a peak ZT of about 0.65. In recent years, many studies have shown a significant enhancement of ZT in other material systems by utilizing a nanostructuring approach to reduce the thermal conductivity by scattering phonons more effectively than electrons. Here we show, using a low-cost and mass-production ball milling and direct-current induced hot press compaction nanocomposite process, that a 50% improvement in the peak ZT, from 0.65 to 0.95 at 800 - 900C is achieved in p-type nanostructured SiGe bulk alloys. The ZT enhancement mainly comes from a large reduction in the thermal conductivity due to the increased phonon scattering at the grain boundaries and crystal defects formed by lattice distortion, with some contribution from the increased electron power factor at high temperatures. Moreover, nanocomposite approaches have been used to study the thermoelectric properties of other material systems such as bismuth telluride (Bi-Te), bismuth antimony (Bi-Sb), and half-Heusler phases. We observed a significant improvement in peak ZT of nanostructured p- and n-type half-Heusler compounds from 0.5 to 0.8 and 0.8 to 1.0 respectively. The ZT improvement is mainly due to the reduction of thermal conductivity. This nanostructure approach is applicable to many other thermoelectric materials that are useful for automotive, industrial waste heat recovery, space power generation, or solar power conversion applications
Thesis (PhD) — Boston College, 2010
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Poydenot, Valier. "BOÎTES ET FILS DE GE SUR SI(001) ORDONNÉS À LONGUE DISTANCE PAR DES RÉSEAUX DE DISLOCATIONS DE FLEXION." Phd thesis, Université Joseph Fourier (Grenoble), 2005. http://tel.archives-ouvertes.fr/tel-00134942.
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L'élaboration de nanostructures semi-conductrices ordonnées, contrôlées en taille et en position, est un enjeu technologique important pour satisfaire les besoins de miniaturisation des circuits actuels de la micro/nano-électronique. Dans cette thèse, une méthode originale d'organisation latérale de nanostructures a été explorée et appliquée au cas de nanostructures de germanium épitaxiées sur silicium (001). Cette technique utilise un réseau de dislocations de flexion proche de la surface libre du substrat, obtenu par collage moléculaire. Un champ de déformation élastique, périodique, se propageant de l'interface de collage jusqu'à la surface des échantillons, nous avons pu obtenir une croissance organisée de nanostructures de germanium.
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Kallel, Houssem. "Étude des propriétés optiques de nanofils individuels de Si, de Ge, et d'alliages et hétérostructures SiGe pour le contrôle de l'absorption et de la diffusion de la lumière." Toulouse 3, 2014. http://thesesups.ups-tlse.fr/2438/.
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Cette thèse porte sur l'étude de la réponse optique de nanofils semiconducteurs individuels afin de déterminer les paramètres clefs contrôlant l'interaction de la lumière avec un nanofil. L'objectif est d'exalter l'absorption pour des applications photovoltaïques ou la diffusion pour le contrôle de l'émission de lumière. Dans un premier temps, des calculs de la réponse optique de nanofils individuels d'alliages Si_{1-x}Ge_{x} effectués dans le cadre de la théorie analytique de Lorenz-Mie, montrent des résonances optiques ajustables dans la gamme du spectre solaire en fonction de la composition x en germanium et du diamètre du nanofil. Ces calculs sont confrontés aux spectres de diffusion élastique obtenus par microscopie optique confocale en champ sombre sur des nanofils isolés de différents diamètres et compositions. Dans un deuxième temps, l'étude théorique de la réponse optique est élargie à des structures complexes de type cœur/gaine Ge/Si et Si/Ge pour optimiser l'efficacité d'absorption par rapport à des nanofils simples, les hétérostructures radiales étant intéressantes dans une cellule solaire à base de nanofils. Enfin, l'optimisation de la diffusion de la lumière et l'exaltation du champ électromagnétique au voisinage du nanofil sont mis en évidence par l'exaltation de la photoluminescence d'un plan de nanocristaux de Si placé dans le champ proche d'un nanofil de Si qui se comporte comme une antenne, par analogie avec les nanostructures plasmoniques. De plus, nous établissons une corrélation entre l'augmentation de l'intensité du champ électrique local induite par la présence du nanofil, calculée par simulations numériques, et l'exaltation de la photoluminescence des nanocristauxIn this thesis is presented a study of the optical response of individual semiconductor nanowires in order to determine the key parameters controlling the interaction of light with a nanowire. The main objective is to enhance either the absorption efficiency for photovoltaic applications or the scattering efficiency for the control of light emission. In a first step, calculations of the optical response of single Si_{1-x}Ge_{x} nanowires performed using the analytical Mie theory, show that optical resonances occur in the solar sun wavelength range. Such resonances can be tuned by changing the nanowire diameter and Ge composition. The calculations are compared to light scattering experiments performed using dark field confocal optical microscopy on single nanowires of different diameter and Ge composition. In a second step, the theoretical study is extended to complex structures such as core-sheath Ge/Si structures to optimize the absorption efficiency compared to simple nanowires. At last, the nanowire-light emitter interaction is evidenced by the polarization dependent photoluminescence enhancement of a Si nanocrystal plane positioned in the near field of a Si nanowire, which one behaves as an optical antenna by analogy with plasmonic nanostructures. Furthermore, we show a correlation between the increase of the local electromagnetic field intensity, obtained by numerical simulations, and the Si nanocrystal photoluminescence enhancement
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Luan, Hsin-Chiao 1969. "Ge photodetectors for Si microphotonics." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8782.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001.Includes bibliographical references (p. 143-157).
This thesis demonstrates the integration of pure Ge near-infrared photodetectors on Si. Ge epilayers were grown directly on Si by a two-step ultra-high-vacuum/chemical-vapor-deposition (UHV/CVD) process. This work conclusively proves that threading-dislocation densities in the Ge epilayers, measured both by plan-view transmission electron microscopy and etch-pit-density (EPD) counting, were reduced by cyclic thermal annealing. Additionally, Ge mesas with no threading dislocations as measured by EPD were also demonstrated. The removal of threading-dislocations can be attributed to the thermal stress induced dislocation glide and reactions. Using the annealed Ge epilayers grown on Si, p-i-n Ge photodetectors with maximum responsivities of 770 mA/W at 1.3 μm were fabricated. Finally, to allow the integration of Ge epilayers in Si microelectronic processing, the protection and passivation of Ge was investigated. The passivation was provided by the oxidation of Si epilayers grown on Ge. Capacitance-voltage characteristics of metal-oxide-semiconductor devices demonstrated the high quality of the passivation with the measured interface state density of 4 x 1011 cm-2eV- 1.
by Hsin-Chiao Luan.
Ph.D.
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Aubel, Dominique. "Apport des techniques de photoémission à la connaissance des hétérostructures Ge/Si(001), Si/Ge(001), Si1-xGex/Si(001) et Si1-xGex/Ge(001)." Mulhouse, 1995. http://www.theses.fr/1995MULH0412.
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Les premières phases de la croissance à température ambiante (TA) et 400°C des deux hétérostructures Si/Ge(001) et Ge/Si(001) ont été étudiées par des techniques de surface comme la spectroscopie de photoélectrons X(XPS) et UV(UPS) et la diffraction d'électrons lents (LEED). Un effort particulier a été fait pour développer la dernière née des méthodes d'investigations structurales dérivée de l'XPS à savoir la diffraction de photoélectrons X(XPD). L'analyse fine de l'émergence des signatures XFD et la mesure des contrastes sur les pics de diffusion vers l'avant en fonction du recouvrement, apportent des renseignements précis concernant l'empilement des atomes dans les couches et donc les modes de croissance initiaux. En second lieu, nous avons élaboré par voie MBE des hétérostructures d'alliages Si1-xGex sur Si(001) pour x faible et Si1-xGex sur Ge(001) pour x fort. Ces couches ont été fabriquées à 400°C par co-évaporation et analysées in situ par XPS, UPS, LEED et par XPD, avant d'être analysées ex situ par XRD, RBS, Raman dans le cadre de différentes collaborations. La conjonction de ces caractérisations ex situ avec nos études de surface in situ, nous a permis de déterminer la qualité cristallographique, la composition en Ge et l'état de contrainte de ces alliages Si1-xGex. La terminaison de surface de ces alliages Si1-xGex a été sondée in situ par des expériences de nitruration initiale qui ont revélé une forte ségrégation du Ge à la surface de ceux-ci. En troisième lieu, des résultats exploratoires sont présentés sur la nitruration thermique des alliages Si1-xGex soulignant la sélectivité de nitruration thermique entre Si et Ge. Contrairement au processus thermique, la nitruration assistée par plasma permet d'obtenir une nitruration simultanée des deux éléments de l'alliage
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Yang, Chih Meng Atwater Harry Albert. "Manipulation of Si and Ge crystallization /." Diss., Pasadena, Calif. : California Institute of Technology, 1997. http://resolver.caltech.edu/CaltechETD:etd-01162008-112621.
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Дубина, В. М. "Термодинамічні властивості розплавів потрійних систем Ge(Si)-Mn-AI, Ge(Si)-Ga-Y та Al-Ga-Y." Diss. of Candidate of Chemical Sciences, КНУТШ, 2004.
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Teichmann, Marc. "Musterbildung auf Si- und Ge-Oberflächen durch niederenergetische Ionenstrahlerosion: Musterbildung auf Si- und Ge-Oberflächen durch niederenergetische Ionenstrahlerosion." Doctoral thesis, Leibniz-Institut für Oberflächenmodifizierung e. V, 2014. https://ul.qucosa.de/id/qucosa%3A13404.
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Die vorliegende Arbeit beschäftigt sich mit der Oberflächenglättung und selbstorganisierten Musterbildung auf Si(100) und Ge(100) durch Beschuss mit niederenergetischen Edelgasionen (Ne, Ar, Kr, Xe). Die Untersuchungen wurden für Ionenenergien zwischen 400 eV und 2000 eV für Ioneneinfallswinkel von 0° bis 85° durchgeführt. Zudem wurde die zeitliche Entwicklung spezifischer Erosionsformen durch die Variation der Fluenz über zwei Größenordnungen analysiert. In den Experimenten finden sich deutliche Anzeichen einer Facettierung sowie einer Vergröberung der Strukturen mit zunehmender Erosionszeit. Diese Beobachtungen deuten darauf hin, dass von Beginn an gradientenabhängiges Zerstäuben und die Reflexion von Primärionen einen wesentlichen Einfluss auf die Strukturentwicklung haben. Die Ergebnisse werden im Kontext bestehender Musterbildungsmodelle diskutiert.
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Ferrando, Villalba Pablo. "Thermal characterization of Si-based nanostructures." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/399339.
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La termoelectricitat és una tecnologia prometedora per recol·lectar energia a partir de diferències de temperatura ambientals. El desenvolupament de materials més eficients que converteixin calor en electricitat d’aquesta manera és necessari per obrir nous espais d’aplicació. S’ha demostrat que nanoestructurar un material és una bona manera d’augmentar la figura de mèrit termoelèctrica a materials cristal·lins per mitjà d’una reducció en la conductivitat tèrmica a causa d’un nombre major de col·lisions de fonons. Aquesta tesi té com a objectiu entendre millor processos que afecten el transport tèrmic a materials basats en silici. Al Capítol 1, una introducció general exposa la necessitat de reduir el consum de combustibles fòssils i en general de fer ús d’energies renovables. També, es raona el benefici de poder alterar les propietats tèrmiques d’un material per millorar l’administració de calor en certs sistemes. Al Capítol 2 es fa un resum de la teoria rere el transport tèrmic. Primer, es deriva l‘equació del calor a través del marc de la termodinàmica clàssica i s’introdueixen els fonons com a quasipartícules que transporten calor. L’aplicació de l’equació de transport de Boltzmann sobre electrons i fonons permet entendre l’efecte de diferents mecanismes de col·lisió a la figura de mèrit dels materials, la qual cosa permet raonar vàries estratègies per millorar-la. Al Capítol 3 es desenvolupen les eines necessàries per mesurar la conductivitat tèrmica de nanomaterials. Primer es preparen 2 criòstats i els seus sistemes de control i després s’explica el desenvolupament de 3 sensors. Les estructures suspeses permeten mesurar la conductivitat en membranes i nanofils. S’explica la seva fabricació i es fa un anàlisi exhaustiu de funcionament i d’incerteses. El mètode 3ω s’introdueix per mesurar la conductivitat a capes primes (en direcció perpendicular al pla) i a materials macroscòpics. Es demostra l’origen del voltatge 3ω i es relaciona amb aquestes conductivitats. Finalment es desenvolupa el sensor de 3ω-Völklein per caracteritzar la conductivitat en el pla de capes primes mentre s’estan creixent. Al Capítol 4 es mesura la conductivitat tèrmica de membranes de Si i es troba la reducció esperada pels efectes de mida, així com efectes de confinament a la membrana de 17.5 nm de gruix. A més s’optimitza la nanolitografia per FIB sobre les membranes amb un estudi sistemàtic, tot trobant una resolució de 200 nm amb una dosi de 50 μC/cm2. Al Capítol 5 s’estudia la conductivitat tèrmica de nanofils porosos de Si amb diferents porositats, longituds i mides. Es troba una tendència de la conductivitat amb el diàmetre dels fils que suggereix que el nucli dels fils és menys porós que la closca. La conductivitat del silici estructural resulta ser 50 vegades menor que la del Si macroscòpic, prometent una bona figura de mèrit. Al Capítol 6 es mesura la conductivitat tèrmica d’unes superxarxes de SiGe novedoses, les quals consten de períodes amb gradients de concentració. Mostren conductivitats molt reduïdes, per sota de la capa prima d’aliatge. La mesura de la superxarxa més gruixuda confirma l’absència d’efectes de coherència dels fonons. Al Capítol 7 es mesura la conductivitat tèrmica d’una membrana de nitrur de silici mentre es dipositen capes de TPD (vidre orgànic) i Indi. Els resultats mostren una reducció inicial en la conductància que no es pot explicar per la llei de Fourier, i que és deguda a l’augment de col·lisions difusives entre els fonons i les vores de la capa. Aquest efecte pot ser extrapolat a altres nanomaterials termoelèctrics, reduïnt la seva conductivitat. També es monitoritza la dinàmica de creixement d’ambdós materials a través de la seva senyal en conductància.Thermoelectricity is a promising technology for scavenging energy from environmental temperature differences. The development of materials that transform heat into electricity in a more efficient way making use of this principle is necessary for opening new application niches. Nanostructuring a material has been demonstrated to increase the thermoelectric figure of merit of crystalline materials via a thermal conductivity reduction driven by enhanced phonon scattering. This thesis is committed to give a better insight into the processes that affect thermal transport in potential Si-based nanomaterials for thermoelectric generation. In Chapter 1, a general introduction exposes the need for reducing fossil fuel consumption and generally using renewable energies. Also, the benefit of tuning the thermal conductivity of materials for thermal management applications is discussed. Chapter 2 provides an overview of the theory behind thermal transport. First, the heat equation is derived from the classical irreversible thermodynamics framework. Then, phonons are introduced as heat carrying quasiparticles. The application of the Boltzmann Transport Equation to both phonons and electrons allows understanding the effect of different scattering mechanisms on the thermoelectric properties of materials. Finally, several strategies for enhancing the figure of merit of materials are reviewed. In Chapter 3, the necessary tools for measuring the thermal conductivity of nanomaterials are developed. Two cryostats are set up along with the temperature control systems that allow measuring at stable temperatures. Later, three sensors are developed for measuring the thermal conductivity of different materials. First, suspended structures intended for measuring the in-plane thermal conductivity of suspended membranes and nanowires are fabricated, and the errors and uncertainties produced in such measurements are characterized. Second, the 3ω method is introduced, allowing the measurement of the out-of-plane thermal conductivity in thin films. The emergence of the 3ω voltage is demonstrated, and the relation between this voltage and the thermal conductivity of the substrate and the thin-film is found. Finally, a sensor for the 3ω-Völklein method is developed, which allows characterizing the in-plane thermal conductivity of thin-films during the layer growth. In Chapter 4, the thermal conductivity of suspended Si membranes is measured, finding the expected reduction in thermal conductivity due to phonon surface scattering, as well as confinement effects in the 17.5 nm thick membrane. Moreover, the nanopatterning of these Si membranes with focused ion beam (FIB) is optimized through a systematic study of its amorphization finding an optimal spatial resolution of 200 nm when using 50 μC/cm2. In Chapter 5, the thermal conductivity of porous Si nanowires is studied for wires with different porosity, length and diameters, showing an unexpected dependence on its diameter that suggests that the wire core is generally less porous than the shell. The structural Si thermal conductivity is found to be one fiftieth of that of the bulk, promising a good thermoelectric figure of merit. In Chapter 6, the thermal conductivity of a novel SiGe graded superlattice is measured, showing a considerable reduction in its thermal conductivity, even below the thin-film alloy limit. The measurement of the thickest superlattice confirms the absence of coherent phonon effects. In Chapter 7, the thermal conductance of a suspended SiNx membrane is measured with a high precision while depositing on it organic (TPD) and metallic (Indium) materials. The results show an initial conductance reduction that cannot be explained with the Fourier law. This reduction is found to be related to an increased diffusive boundary scattering, which could be easily extrapolated to other thermoelectric nanomaterials, reducing their thermal conductivity. Also, the growth dynamics of both materials are characterized through their signal in the conductance.
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White, Julian Darryn. "Phonons in (Si)_m/(Ge)_n superlattices." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239759.
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Camacho-Aguilera, Rodolfo Ernesto. "Ge-on-Si laser for silicon photonics." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82173.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 253-263).
Ge-on-Si devices are explored for photonic integration. Importance of Ge in photonics has grown and through techniques developed in our group we demonstrated low density of dislocations (<1x109cm-2) and point defects Ge growth for photonic devices. The focus of this document will be exclusively on Ge light emitters. Ge is an indirect band gap material that has shown the ability to act like a pseudo direct band gap material. Through the use of tensile strain and heavy doping, Ge exhibits properties thought exclusive of direct band gap materials. Dependence on temperature suggests strong interaction between indirect bands, [Delta] and L, and the direct band gap at [Gamma]. The behavior is justified through increase in photoluminescence on Ge. The range of efficient emission is to 120° with the first band interaction, and above 400° on the second band interaction. Low defect concentration in Ge is achieved through chemical vapor deposition at high vacuum (~1x10-8 mbar) in a two-step process. The high temperature growth and low concentration of particles permits epitaxial growth with low defect concentration. Chemical selectivity forbids Ge growth on oxide. Oxide trenches permit the growth on Si for a variety of shapes, without detrimentally affecting the strain of the Ge devices. Dopant concentration above intrinsic growth concentration, ~1x1019cm-3 phosphorus, have been achieved through a series of methods non-CMOS, spin-on dopant; and CMOS, implantation and delta doping. All the techniques explored use enhanced dopant diffusion observed in Ge under heavy n-type doping. A dopant source, or well, is used to distribute the dopants in the Ge without increasing the defect concentration. The approach lead to the development of electrically injected devices, LEDs and LDs. Ge pnn double heterostructure diodes were made under low, ~1x1018cm-3, and heavy n-type doping, >1x1019cm-3. Both devices showed improved performance compared to pin Ge LED. Furthermore, heavy doped Ge diodes exhibit evidence of bleaching or transparency. The techniques described permitted the development of Ge-on-Si laser with a concentration ~1-2x1019cm-3. It is the first demonstration of a Ge laser optically pumped working under the direct band gap assumption like other semiconductors. It represents the evidence of carrier inversion on an indirect band gap semiconductor. With 50cm-1 gain, the material shows Fabry-Perot cavity behavior. Finally, we demonstrated a fully functioning laser diode monolithically integrated on Si. Ge pnn lasers were made exhibiting a gain >1000cm-1 and exhibiting a spectrum range of over 200nm, making Ge the ideal candidate for Si photonics.
by Rodolfo E. Camacho-Aguilera.
Ph.D.
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Okyay, Ali Kemal. "Si-Ge photodetection technologies for integrated optoelectronics /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Van, Sothachett. "Elaboration des interfaces Ge/Si(111) et Ge/Si(100) par UHV-CTLCVD : caractérisation par ARUPS, XPD et LEED." Mulhouse, 1994. http://www.theses.fr/1994MULH0322.
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Le travail que nous présentons dans ce mémoire est centré sur l'élaboration des interfaces Ge/Si(111) et Ge/Si(100) par le dépôt chimique en phase vapeur à très basse pression (UHV-CTLCVD pour Ultra High Vacuum Chemical Vapor Deposition) utilisant le germane comme source gazeuse. Nous avons en premier lieu étudié les réactivités du germane (catalytiquement décomposé ou non) vis-à-vis des surfaces Si(111)7x7 et Si(100)2x1. Nous avons alors montré que la décomposition catalytique du germane est très intéressante, surtout pour la croissance de Ge à basses températures (<400°C). En particulier, dès la température ambiante, un dépôt appréciable de Ge a été possible, grâce à la chimisorption des espèces GeH, GeH2 et GeH3. Ces espèces précurseurs de l'adsorption ont été alors pour la première fois, identifiés par photoémission. Nous avons ensuite examiné l'évolution de la structure et de la morphologie des interfaces Ge/Si(111) et Ge/Si(100) élaborées par UHV-CTLCVD, en fonction de la température de croissance et de recuit. En particulier, pour une température de l'ordre de 400°C, les couches de Ge déposées présentent une bonne cristallinite, avec une reconstruction de surface 5x5 dans le cas de l'interface Ge/Si(111) et 2x1 dans le cas de l'interface Ge/Si(100). L'influence de l'hydrogène atomique sur les surfaces Si(111):Ge5x5, Si(111):Ge7x7 et Si(100):Ge2x1 a également été étudié. Les hétérostructures Si/Ge/Si(111) et Si/Ge/Si(100), préparées à basses températures (<400°C), présentent une assez bonne cristallinite. Cette élaboration, par notre technique de dépôt, a été possible grâce à la présence en surface de l'hydrogène atomique produit lors de la décomposition de la source gazeuse, l'hydrogène jouant le rôle de surfactant dans le processus de croissance. Par ailleurs, nous avons complété notre étude expérimentale par une étude théorique ou nous avons examiné les premiers stades d'adsorption de Ge sur Si(111)7x7 par la méthode de Hückel (EHT)
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Guangnan, Zhou. "Impact of doping on epitaxial Ge thin film quality and Si-Ge interdiffusion." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62996.
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Germanium-on-silicon (Ge-on-Si) structure-based semiconductor devices are playing an increasingly important role in large-scale dense photonic integration, especially in silicon (Si) photonics. Si photonics has emerged as an effective solution to overcome the wiring limit imposed on integrated circuits with continued scaling by using optical interconnects instead metal interconnects. A Si-compatible laser is the last missing piece in optical interconnects on Si platforms. Recently, III-V lasers on Ge/Si substrates and Ge-on-Si lasers were demonstrated as the most promising candidates, in which Ge layers function as either the transition layers or the optical gain layers.
For different applications, the requirements on Ge film quality and Ge/Si interface interdiffusion are different. Si-Ge interdiffusion during high-temperature growth or fabrication steps changes the distribution of Ge and increases atomic intermixing, which degrades device performance. However, studies on the doping impact on Ge film quality and Si-Ge interdiffusion are very limited, which were addressed in this work.
We investigate Ge-on-Si film quality systematically under different types of doping conditions (phosphorus, arsenic and boron) for the first time. It’s found that the boron doping significantly impairs the Ge film quality, while arsenic and phosphorus can effectively reduce the threading dislocation density without the commonly used defect annealing. This provides a new method to fabricate high-quality Ge-on-Si films, which can avoid undesired Si-Ge interdiffusion.
Si-Ge interdiffusion with different doping at Ge/Si interfaces has been investigated experimentally and theoretically. The enhancement of interdiffusion was observed in n-type (phosphorus and arsenic) doped Ge-on-Si. The phenomenon is attributed to the Fermi-level effect. A quantitative model of Si-Ge interdiffusion under high n-type doping was proposed. The model agrees well with the experimental data. This is also the first study on the quantitative modeling of Si-Ge interdiffusion with high n-type doping across the full Ge range.
This work is of technical significance for the structure, doping and process design of Ge-on-Si structure-based devices including the two laser types mentioned above, Ge modulators and Ge photodetectors.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Fink, Andreas. "Organische Moleküle auf Halbleitern: Adsorption und elektronische Struktur ungesättigter Kohlenwasserstoffe auf Si(100)-, Ge/Si(100)- und Ge(100)-Oberflächen." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=96278673X.
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Tolstoguzov, A., B. Ber, P. Chapon, and M. N. Drozdov. "Depth Profiling of Multilayer Mo/Si Nanostructures." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35262.
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A round-robin characterization is reported on the sputter depth profiling of [60(3.0 nm Mo/ 0.3 nm B4C/ 3.7 nm Si)] and [60 (3.5 nm Mo/ 3.5 nm Si)] stacks deposited on Si (111). Two different commercial secondary ion mass spectrometers with time-of-flight and magnetic-sector analyzers and a pulsed radio frequency glow discharge optical emission spectrometer were used. The pros and cons of each instrumental approach are discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35262
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Piels, Molly. "Si/Ge photodiodes for coherent and analog communication." Thesis, University of California, Santa Barbara, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3612014.
Full textAbstract:
High-speed photodiodes have diverse applications in wireless and fiber communications. They can be used as output stages for antenna systems as well as receivers for fiber optic networks. Silicon is an attractive substrate material for photonic components for a number of reasons. Low cost manufacturing in CMOS fabrication facilities, low material loss at telecommunications wavelengths, and relatively simple co-packaging with electronics are all driving interest in silicon photonic devices. Since silicon does not absorb light at telecommunications wavelengths, photodetector fabrication requires the integration of either III-V materials or germanium. Recent work on germanium photodetectors has focused on low-capacitance devices suitable for integration with silicon electronics. These devices have excellent bandwidth and efficiency, but have not been designed for the levels of photocurrent required by coherent and analog systems. This thesis explores the design, fabrication, and measurement of photodetectors fabricated on silicon with germanium absorbing regions for high speed and high power performance.
There are numerous design trade-offs between speed, efficiency, and output power. Designing for high bandwidth favors small devices for low capacitance. Small devices require abrupt absorption profiles for good efficiency, but design for high output power favors large devices with dilute absorption. The absorption profile can be controlled by the absorber layer thickness, but this will also affect the bandwidth and power handling. This work quantifies the trade-offs between high speed, high efficiency, and high power design. Intrinsic region thickness and absorption profile are identified as the most important design variables. For PIN structures, the absorption profile and intrinsic region thickness are both functions of the Ge thickness, but in uni-traveling carrier (UTC) structures the absorption profile and intrinsic region can be designed independently. This allows optimization of the absorption profile independently from the RC-limited frequency response and compression current and ultimately enables larger saturation current-bandwidth products. This thesis includes the first theory, fabrication, and measurement of a uni-traveling carrier photodiode on the Si/Ge platform. Key contributions include an accurate nonlinear device model and a complete set of processes and design rules for fabricating Ge devices in the UCSB nanofab. The UTC structure is shown to be useful in extending the bandwidth and power handling capabilities of waveguide-integrated photodiodes, especially at high frequencies.
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Živanović, Goran. "Design considerations for Ge-on-Si waveguide photodetector." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91083.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.45
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 108-114).
In integrated photonic circuits photodetector is one of key components, modern applications require that photodetector has a high 3 dB bandwidth. The ultimate limit for the response time for conventional photodetectors (like vertically illuminated photodiode, Schotky photodiode, MSM photodetector etc.) is given by the transit time of the photogenerated electron-hole pairs, it can not be minimised by decreasing the thickness of the depletion region without reducing quantum efficiency (i.e. the fraction of the incident light that is absorbed). Waveguide photodetectors have been developed to overcome this trade-off. In the waveguide photodetector light propagates in a direction that is parallel to the junction interfaces and is perpendicular to the drift of the generated electron-hole pairs. This geometry decouples absorption length from the drift length. Therefore the waveguide photodetector can have both a very thin active region for short transit time and a long absorption length for a high quantum efficiency. In this thesis , I designed germanium on silicon photodetector. The main designing tool was full vectorial 3D Finite Difference Time Domain (FDTD) simulator. Bandwidth-efficiency product was used as the main figure of merit. The input is silicon rib waveguide, which is optimised to maximize transmitted power. For optimal dimensions of the device calculated responsivity is 0.94 A/W, efficiency is 83 %, bandwidth is 64 GHz and bandwidth x efficiency product is 53 GHz.
by Goran Živanović.
S.M.
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Silva, Marcos Antonio Araujo. "Espalhamento Raman em heteroestruturas semicondutoras de Si/Ge." [s.n.], 1995. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277744.
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Orientador: Fernando CerdeiraTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-07-20T17:20:50Z (GMT). No. of bitstreams: 1 Silva_MarcosAntonioAraujo_D.pdf: 2541195 bytes, checksum: 3f6719299d5a08183c7b43e174b72215 (MD5) Previous issue date: 1995
Resumo: Nós utilizamos espectroscopia Raman para estudar a dinâmica de rede de heteroestruturas semicondutoras de Si/Ge, tanto experimental quanto teoricamente. Foi feito um estudo de uma ampla região espectral, (de ~ 2 cm-1 até 600 cm-1), que inclui fônons acústicos dobrados, fônons de interface, e fônons ópticos confinados. Nós utilizamos vários sistemas experimentais: um sistema usual, um sistema de alta resolução, e um sistema de micro-Raman. Pelo lado teórico, nós aplicamos o modelo da cadeia linear unidimensional, com interação de até segundos vizinhos, e usamos o modelo bond-polarizability para simular os espectros Raman. Uma análise fenomenológica nos permitiu verificar a presença de rugosidade de larga escala (terraços) nas interfaces de nossas amostras. Medidas de espalhamento Raman ressonante também foram feitas para os fônons ópticos de nossas microestruturas. Uma análise quantitativa da seção de choque Raman do pico originado nas vibrações confinadas Ge-Ge, permitiu-nos acompanhar as transições ópticas dos éxcitons confinados em cada terraço. Esta análise favorece nossas interpretações anteriores a respeito desta transição, que a relaciona a transições do tipo E1 do Ge bulk
Abstract: We have used Raman spectroscopy to study the lattice dynamics of Ge/Si semiconductor heterostructures, both experimentally and theoretically. The study was performed in a broad spectral range (from 2 cm-1 up to 600 cm-1), which includes the acoustical folded phonons, interfaces phonons, and confined optical phonons. We have used several experimental systems: a standard, a high resolution, and a micro-Raman setup. Theoretically, we have applied a one-dimensional linear-chain model with second-neighbor interactions to obtain the vibrational modes and a bond-polarizability model to simulate the Raman spectra. A phenomenological analysis allows us to verify the presence of large scale roughness (terraces) in the interfaces of our samples. Resonant Raman measurements were also performed for the optical phonons of our microstructures. Quantitative analysis of the resonant-Raman cross-section of the peak originating in Ge-Ge confined vibrations allows us to single out optical transitions of excitons confined within each terrace. This analysis favours our previous interpretation of this transition, which relates it to the E1-transitions of bulk Ge
Doutorado
Física
Doutor em Ciências
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Малецький, М. А. "Фотоелектричні властивості тонких напівпровідникових плівок Ge та Si." Master's thesis, Сумський державний університет, 2020. https://essuir.sumdu.edu.ua/handle/123456789/82012.
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Мета кваліфікаційної роботи магістра полягала у аналізі результатів та
вивченні явища фотоефекту у тонких напівпровідникових плівках германію та
кремнію, визначення чутливості плівкових зразків до дії зовнішнього
опромінення у залежності від їх товщини.
Під час виконання роботи використовувалися такі методи як термічне
випаровування у вакуумі для одержання зразків, оптична інтерферометрія для
визначення товщини та резистометрія для дослідження впливу опромінювання
на величини опору плівок. В якості приладів використовувались установка
ВУП-5М, інтерферометр МІІ-4, світлофотометр.
У результаті проведених досліджень було проведено дослідження явища
фотоефекту в тонких плівках Ge i Si та визначено коефіцієнт чутливості К, який
показує як змінюється питомий опір зразка при зміні інтенсивності джерела
випромінювання. Встановлено, що величина коефіцієнта К при зростанні
товщини зменшується.
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Gan, Wei. "Precipitation and strengthening in AL-GE-SI alloys." The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1135275701.
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Pulido, Junquera Maria Angeles. "Estudio computacional de las Si, Ge, F-zeolitas." Doctoral thesis, Universitat Politècnica de València, 2008. http://hdl.handle.net/10251/1867.
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En el presente trabajo se estudia el papel de las moléculas orgánicas, de los átomos de Ge y de los aniones fluoruro, F-, en la síntesis de materiales zeolíticos mediante el uso de técnicas computacionales basadas en mecánica molecular y métodos químico cuánticos. El estudio de los distintos términos energéticos que componen la energía total del sistema permite analizar el papel de los cationes pentametonio, hexametonio, heptametonio y octametonio en la síntesis de las estructuras EUO, ITH, IWR e IWW puramente silíceas.
La substitución isomórfica de Si por Ge es estudiada en las estructuras AST, ASV, BEA, BEC, ISV, ITH, IWR, IWW y se analizan los términos energéticos implicados en dicha substitución. Además, se analizan los factores que puedan estar implicados en la localización preferencial de los átomos de Ge en las unidades D4R (Double Four Membered Ring). Finalmente, se analiza la variación de la estabilidad termodinámica de las estructuras BEA, BEC e ISV con diversos contenidos en Ge.
La localización y papel del anión fluoruro en las Si,F-zeolitas es estudiado mediante el análisis de los factores implicados en la distribución del anión fluoruro en la red de las estructuras IFR, ITH, STF y STT pura sílice. Posteriormente, se estudió la distribución del anión fluoruro en las estructuras IFR, ITH, STF y STT en presencia de las moléculas orgánicas utilizadas como ADEs orgánicos en la síntesis de las zeolitas pura sílice. El conocimiento adquirido en el estudio del anión fluoruro fue utilizado para analizar la distribución del F en la estructura IWR, cuya distribución no es totalmente conocida experimentalmente.
La localización de los átomos de Ge en las unidades D4R es estudiada mediante la simulación del espectro de RMN de 19F combinando técnicas de química computacional basadas en potenciales interatómicos y de primeros principios. Inicialmente se realizó el estudio de la metodología que permita una adecuada descripción de las señales observadas experimentPulido Junquera, MA. (2006). Estudio computacional de las Si, Ge, F-zeolitas [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1867
Palancia
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El, Kadib Abdelkrim. "Métallation (Si, Ge) des esters méthyliques d'acides gras." Toulouse 3, 2004. http://www.theses.fr/2004TOU30185.
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Ce travail décrit la métallation (Si, Ge) des esters méthyliques d'acides gras (EMAG) et de l'huile brute. Dans un premier temps, l'hydrométallation des EMAG a été développée. La séquence d'initiation radicalaire conduit à des produits métallés avec une meilleure sélectivité. La silylation des EMAG en α de la fonction ester a été réalisée par des silyltriflates ou à partir d'énolates d'EMAG. L'optimisation des conditions opératoires a conduit à l'obtention exclusive des produits C-silylés. Le quatrième chapitre a porté sur l'obtention de biosilicones par polycondensation des silylEMAG. La modélisation moléculaire a révélé "le masquage" parfait des siloxanes par des EMAG montrant l'intérêt que peuvent présenter de tels polymères en particulier concernant l'accroissement de leur biocompatibilité. Dans le dernier chapitre a été développé une application intéressante des précurseurs silylés : le pouvoir d'auto-organisation de ces unités moléculaires a permis d'accéder à des nanomatériaux de siliceThe present work describes the metalation (Si, Ge) of fatty acid methyl esters (FAME) and raw fish oil. In the first time, the hydrometalation of FAME has been carried out. The free-radical initiation sequence led to metal embedded products with a better selectivity. The a-silylation of the ester functional group of FAME was detailed, whether through silyltriflates or from the respective enolates of the FAME. For each procedure, the optimization of the operational conditions drove to obtaining exclusive of C-silylated products. The fourth chapter detailed obtaining biosilicones by polycondensation of the silylated FAME. Molecular modelling revealed an almost perfect "bio-masking" of the siloxanes by the FAME, thus showing the high interest that of these polymers can present concerning their growth regarding biocompatibility. In the last chapter a particularly interesting application of the silylated precursors has been developed: the ability of self-reorganisation of these molecular units allowed producing silica-based nanomaterials
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Robinson, Dirk J. "High speed data converter circuits in SI-GE." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Dissertations/Fall2008/d_robinson_121008.pdf.
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Thesis (Ph. D.)--Washington State University, December 2008.Title from PDF title page (viewed on Jan. 15, 2009). "School of Electrical Engineering and Computer Science." Includes bibliographical references (p. 60-61).
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Sivadasan, Vineet. "Strain relaxation study of Si1-xGex & Ge buffer layers on Si(001) and InSb on Ge/Si(001) virtual substrates." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/89938/.
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Due to their direct and tuneable bandgap, III-V semiconductors offer variations in electrical properties, compared to silicon. However wafers of III-V materials are more expensive to manufacture and have higher defect densities than Si(001). Epitaxially depositing high quality thin films of III-V materials onto Si(001) substrates offers a more cost effective route to manufacturing state of the art III-V electronic devices, whilst mitigating defect generation through lattice and thermal expansion coefficient mismatches. In this study, pure Ge and Si1−xGex layers are deposited as thin film heterostructures on on-axis and 6° off-axis Si(001) substrates using reduced pressure chemical vapour deposition to act as strain tuned “buffer layers” to integrate a particular III-V compound onto the substrate. The films are characterised using transmission electron microscopy (TEM), atomic force microscopy (AFM), high resolution X-ray diffraction (HR-XRD) and defect etching & differential interference contrast (DIC) optical microscopy. The first key finding in this study relates to the development of an 78nm Ge buffer which is comprised of a LT seed layer followed by controlled annealing only and at a fraction of the tensile strain of state of the art thick LT/HT Ge buffer layers. The second key finding comes from the comparisons between the established linear Si1−xGex grading (LG) process with the recently developed reverse linear Si1−xGex/Ge grading (RLG) process. Continuous tensile strain relaxation in RLG even up to x=0.45 yields high quality buffer layers with ≤ 3.7nm roughness, ×107cm−2 TDD and consistently delivering 0.2% tensile strain albeit with a rise in stacking faults past 70% Ge. The third major discovery comes when omitting the reverse graded layer entirely in the RLG structure and depositing a constant composition Si1−xGex step on the Ge buffer layer. High misfit dislocation densities and surface roughening is observed leading to the formation of Kirkendall voids in the Ge underlayer as a strain relieving mechanism. 5 The final chapter of this study investigates solid source molecular beam epitaxy growth of high quality indium antimonide which has the highest lattice mismatch of any III-V compound to Si(001) at 19.3% using the highest quality pure Ge buffer layers on 6° off-axis Si(001). HR-XRD reciprocal space maps shows identical levels of strain in Ge buffer layers grown on on-axis and 6° off-axis substrates, however an increased degree of tilt is measured in the off-axis Ge buffer layer, with reduced degree of tilt in the InSb layer.
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Goh, Johnathan Jian Ming. "Commercialization potential of compositionally graded Ge - Si₁₋x̳Gex̳ - Si substrates for solar applications." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38550.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.In title on t.p., double-underscored "x" appears as subscript.
Includes bibliographical references.
This project considers the potential of Ge - Si₁₋x̳Gex̳ - Si substrates for solar applications. The use of compositionally graded substrates to achieve heterointegration across different materials platforms such as Si, Ge and GaAs has proven successful and dual junction solar cells have been fabricated on such substrates. The potential for graded substrates in the solar market is discussed considering the current technology, market players and worldwide renewable energy policies. A cost model is also developed and analyzed in the course of writing to assess the feasibility of this commercial enterprise. The result of these analyses highlights the technical and commercial viability of graded substrates in the solar market.
by Johnathan Jian Ming Goh.
M.Eng.
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Nguyen-Duc, Trung-Kien. "Croissance épitaxiale et propriétés optiques des îlots auto-assemblés Ge/Si et des super-réseaux de courte période Ge(m)Si(n)." Aix-Marseille 2, 2005. http://theses.univ-amu.fr.lama.univ-amu.fr/2005AIX22086.pdf.
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Menard, Stéphane. "Propriétés optiques et électriques des nanostructures Si/CaF2." Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10235.
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Ce travail porte sur l'etude des proprietes optiques et electriques des nanostructures de si/caf 2. A partir d'une meme technique d'elaboration, nous parvenons a fabriquer deux categories differentes d'echantillons. Les echantillons de type multipuits elabores par epitaxie par jets moleculaires sur un substrat maintenu a la temperature ambiante presentent des couches nanocristallines, composees de grains d'un diametre moyen de 15 a pour les couches de si et de 30 a pour les couches de caf 2. Ces structures multipuits evoluent vers une seconde categorie, une structure colonnaire, apres recuit sous ultravide a 450\c pendant 30 mn. Les colonnes sont composees de grains d'un diametre moyen de 200-300 a, eux-memes composes de grains de si et de caf 2. Nous montrons que ces deux classes d'echantillons possedent une caracteristique optique remarquable qui est la photoluminescence a temperature ambiante, et dont les caracteristiques sont en de nombreux points comparables aux resultats connus sur le silicium poreux. Dans le cas des echantillons multipuits, nous relions cette photoluminescence au confinement quantique des electrons dans les grains de si. Cependant, les resultats d'absorption optique montrent une difference de plus de 1 ev entre la valeur de la bande interdite et l'energie de photoluminescence. Ceci souligne le role important des etats de surface dans le mecanisme de photoluminescence des nanostructures de silicium. Dans le cas des echantillons de type multipuits ou colonnaires, ce dernier point est confirme par l'importance de la passivation pour l'obtention d'une photoluminescence intense. Nous avons etudie les proprietes electriques des structures multipuits. Nous observons une resistance differentielle negative de la caracteristique i-v que nous attribuons au piegeage d'electrons par les defauts cristallins de ces nanostructures.
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Wigblad, Dan. "Structural and optical characterization of Si/Ge quantum dots." Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11672.
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In this study silicon-germanium quantum dots grown on silicon have been investigated. The aim of the work was to find quantum dots suitable for use as a thermistor material. The quantum dots were produced at KTH, Stockholm, using a RPCVD reactor that is designed for industrial production.
The techniques used to study the quantum dots were: HRSEM, AFM, HRXRD, FTPL, and Raman spectroscopy. Quantum dots have been produced in single and multilayer structures.
As a result of this work a multilayer structure with 5 layers of quantum dots was produced with a theoretical temperature coefficient of resistance of 4.1 %/K.
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Wietler, Tobias [Verfasser]. "Surfactant-modifizierte Epitaxie für Ge/Si-Heterobauelemente / Tobias Wietler." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover, 2010. http://d-nb.info/1010987275/34.
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Teichmann, Marc. "Musterbildung auf Si- und Ge-Oberflächen durch niederenergetische Ionenstrahlerosion." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-175110.
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Die vorliegende Arbeit beschäftigt sich mit der Oberflächenglättung und selbstorganisierten Musterbildung auf Si(100) und Ge(100) durch Beschuss mit niederenergetischen Edelgasionen (Ne, Ar, Kr, Xe). Die Untersuchungen wurden für Ionenenergien zwischen 400 eV und 2000 eV für Ioneneinfallswinkel von 0° bis 85° durchgeführt. Zudem wurde die zeitliche Entwicklung spezifischer Erosionsformen durch die Variation der Fluenz über zwei Größenordnungen analysiert. In den Experimenten finden sich deutliche Anzeichen einer Facettierung sowie einer Vergröberung der Strukturen mit zunehmender Erosionszeit. Diese Beobachtungen deuten darauf hin, dass von Beginn an gradientenabhängiges Zerstäuben und die Reflexion von Primärionen einen wesentlichen Einfluss auf die Strukturentwicklung haben. Die Ergebnisse werden im Kontext bestehender Musterbildungsmodelle diskutiert.
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Kim, Meekyung Ph D. Massachusetts Institute of Technology. "Limited-area growth of Ge and SiGe on Si." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/62743.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 147-159).
The goal of this thesis is to develop and understand processing conditions that improve the surface morphology and reduce the dislocation density in limited-area heteroepitaxy of Ge and SiGe on Si (100) substrates. Low pressure chemical vapor deposition was investigated for two limiting cases of strain states: thin, strained, high Ge content SiGe films for transistor applications, and thick, relaxed Ge films, for potential optoelectronic applications. Selective epitaxial growth of thin, high Ge-content, strained SiGe on oxide-patterned silicon was studied, specifically the effect of growth area on the critical thickness. The critical thickness of Sio.33Geo.67 formed by selective epitaxial growth in areas of 2.3 x 2.3 [mu]m was found to be 8.5 nm, which is an increase of 2x compared to the critical thickness observed for growth in large areas (i.e. for non-selective epitaxy). The sources of misfit dislocation nucleation in selective growth were analyzed, and misfit generation from the SiGe pattern edges, due to effects such as local strain concentration, Si surface shape near the oxide boundary, and preferential SiGe growth near the pattern edge were investigated. Thin, smooth Ge-on-Si films were developed and the effect of growth conditions on film morphology was examined to find an optimum temperature and pressure for smooth film surface (365 °C and 60 torr). A period of delayed epitaxial growth, or "incubation time" was observed, and a Si surface treatment technique, consisting of a short SiGe pulse, with negligible SiGe thickness, was employed to realize uniform Ge films with low surface roughness (RMS<0.3 nm) and reduced incubation time (<20 seconds). For selective growth of relaxed, thick Ge, approximately 1 pm-thick Ge films were grown in exposed Si regions on oxide-patterned wafers, and germanium selectivity, faceting, surface roughness and threading dislocation density were studied as functions of growth and processing conditions. The optimal growth condition for relaxed Ge selective epitaxial growth was found (750 °C and 10 torr, with 100 sccms of GeH4 and 10 slpm H2 flow), and the effect of thermal annealing, Ge film thickness, and growth area on the threading dislocation density was also studied.
by Meekyung Kim.
Ph.D.
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Paul, Neelima [Verfasser]. "Bi surfactant mediated growth for fabrication of Si/Ge nanostructures and investigation of Si/Ge intermixing by STM / vorgelegt von Neelima Paul." 2007. http://d-nb.info/987093444/34.
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