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1
Beaudoin, Mario. "Electrical transport properties of n-Type InP." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61237.
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InP obtained by metal-organic vapor phase epitaxy, with properties similar to GaAs, shows mobilities approaching the theoretical maxima at low temperatures. However, the corresponding values remain abnormally low at room temperature where a pronounced electronic excitation to the conduction band is observed simultaneously. This reduction of the mobility is attributed to the presence of deep centers that are electrically inactive at low temperatures but become excited when the temperature increases. A model based on an iterative solution to the Boltzmann equation and accounting for the usual scattering mechanisms, including inelastic interactions, is able to explain the data perfectly and shows that a very high mobility at low temperature is not a sufficient measure of the purity for this material. The binding energy of the deep centers depends on the organo-metalic source used for the growth. This links the solution of this problem to the purification of the chemicals. Depletion effects at the interfaces did not appear to be significant. (Abstract shortened by UMI.)
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Tudury, Heloisa Andrade de Paula. "Gap direto-indireto em poços quânticos de camadas tensionadas de InGaAs/InP." [s.n.], 2001. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277786.
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Orientador: Fernando IikawaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica "Gleb Wataghin"
Made available in DSpace on 2018-08-02T02:53:03Z (GMT). No. of bitstreams: 1 Tudury_HeloisaAndradedePaula_M.pdf: 2460328 bytes, checksum: a3be30d81a490ff71b29d80aaf37993f (MD5) Previous issue date: 2001
Resumo:Estudamos a transição de gap direto-indireto em poços quânticos de dopagem modulada de camadas tensionadas de In1-xG axAs/InP. As amostras analisadas foram crescidas por LP-MOCVD. Os poços quânticos têm largura de 6 nm com concentrações de gálio entre x = 0.47 e 0.60. O objetivo da dissertação foi analisar a evolução da estrutura de banda em função da concentração de Ga por medidas ópticas. Realizamos medidas de fotoluminescência com a temperatura da amostra variando entre 2 e 100 K. Observamos que a forma de linha de fotoluminescência é bastante sensível à composição de Ga na liga. Cálculos teóricos baseados no hamiltoniano de Luttinger-Kohn explicam qualitativamente esse comportamento dos espectros, mostrando que realmente há influência da estrutura de bandas nos mesmos. Nos dados experimentais também observamos efeitos de localização possivelmente provenientes da flutuação do potencial da liga, rugosidade das interfaces e defeitos criados pela presença da tensão intrínseca. Realizamos também medidas de fotoluminescencia na presença de uma pressão biaxial externa, utilizando uma célula de pressão baseada na deformação de placa construída em nossos laboratórios, para verificar se o comportamento observado nos espectros de fotoluminescência em diferentes amostras é realmente devido a mudança na estrutura de banda. Os espectros de fotoluminescência medidos na presença de pressão externa mostram realmente as mesmas características - variação na forma da linha de emissão - atribuídas a mudança de gap direto para indireto à medida que aumenta a pressão externa, efeito equivalente àquele decorrente do aumento da concentração do Ga em diferentes amostras. Isso fortalece a nossa interpretação de que o efeito da estrutura de bandas é um dos responsáveis pelo comportamento apresentado nos espectros de fotoluminescência. Este trabalho abre a possibilidade de realizar estudos de efeitos dependentes da estrutura de bandas em poços quânticos aplicando pressão biaxial externa
Abstract:We have studied the direct-to-indirect gap transition in strained-layer modulation-doped In1-xGaxAs/InP quantum wells. The samples were grown by LP-MOCVD. The quantum wellthickness is 6 nm and their Ga content was varied from x = 0.47 to 0.60. Our purpose is to study the influence of Ga content variation on the band structure by optical measurements. Photoluminescence measurements were performed under temperatures varying from 2 to 100K. We have observed that the photoluminescence line shape is very sensitive to the Ga composition in the alloy. Theoretical calculations based on Luttinger-Kohn Hamiltonian explain qualitatively the behavior of the photoluminescence spectra, showing the influence of the valence band structure on them. Our experimental data also show localization effects, possibly arose from the alloy potential fluctuation, interfaces roughness and defects created due to the built-in strain. We also carried out photoluminescence measurements under an externally applied biaxial strain, using a pressure cell based on a plate bending method, in order to verify whether the behavior observed in photoluminescence spectra in different samples is due to the band structure effects. The photoluminescence spectra measured in the presence of an external strain show similar behavior to those observed when the Ga concentration is changed in different samples due to the changing the band structure from direct to indirect-gap. This result reinforces that the band-structure effect is responsible for the behavior observed in photoluminescence spectra. This work opens the possibility of further research on the band-structure dependent effects on quantum wells under externally applied biaxial strain
Mestrado
Física
Mestra em Física
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Hatami, Fariba. "Indium phosphide quantum dots in GaP and in In 0.48 Ga 0.52 P." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2002. http://dx.doi.org/10.18452/14873.
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Im Rahmen dieser Arbeit wurden selbstorganisierte, verspannte InP-Quantenpunkte mittels Gasquellen-Molekularstrahlepitaxie hergestellt und deren strukturelle und optische Eigenschaften untersucht. Die Quantenpunkte wurden sowohl in InGaP-Matrix gitterangepasst auf GaAs-Substrat als auch in GaP-Matrix auf GaP-Substrat realisiert. Die starke Gitterfehlanpassung von 3,8% im InP/InGaP- bzw. 7,7% im InP/GaP-Materialsystem ermöglicht Inselbildung mittels des Stranski-Krastanow-Wachstumsmodus: Ab einer kritischen InP-Schichtdicke findet kein zweidimensionales, sondern ein dreidimensionales Wachstum statt. Die kritische Schichtdicke wurde mit etwa 3 Monolagen für das InP/InGaP- und mit etwa 1,8 Monolagen für das InP/GaP-System bestimmt. Die strukturellen Untersuchungen zeigen, dass InP Quantenpunkte in GaP im Vergleich zu solchen in InGaP größer sind und stärker zum Abbau von Verspannung tendieren. Die in InGaP-Matrix eingebettete InP-Quantenpunkte zeigen sehr ausgeprägte optische Emissionen, die, in Abhängigkeit von den Wachstumsparametern, im Bereich von 1,6 bis 1,75eV liegen. Die Emissionslinie wird der strahlenden Rekombination von in den Quantenpunkten lokalisierten Elektronen und Löchern zugeordnet. Dies wird auch durch das Bänderschema bestätigt, das mit Hilfe der Model-Solid-Theorie modelliert wurde. Darüber hinaus weist die Lebensdauer der Ladungsträger von einigen hundert Pikosekunden darauf hin, dass die InP/InGaP Quantenpunkte vom Typ I sind. Zusätzlich zu den optischen Eigenschaften wurde die Anordnung von dicht gepackten InP-Quantenpunkten in und auf InGaP mittels zweidimensionaler Fourier-Transformation der Daten aus der Atomkraftmikroskopie, Transmissionelektronmikroskopie und diverser Röntgen-Streuexperimente untersucht sowie die planaren und vertikale Ordnungseffekte der Quantenpunkte studiert. Die Untersuchungen zeigen, dass die Ordnung der Quantenpunkte sowohl hinsichtlich ihrer Packungsdichte als auch ihrer Orientierung mit wachsender InP-Bedeckung zunimmt. Darüber hinaus wurde die Verspannungsverteilung in den InP/InGaP-Quantenpunkten mit Hilfe von diffuser Röntgen-Streuung in Verbindung mit kinematischen Simulationen studiert und eine asymmetrische Form der Quantenpunkte festgestellt, die auch Ursache für die gemessene Polarisationsanisotropie der Photolumineszenz sein kann. Die in GaP-Matrix eingebetteten InP-Quantenpunkte wurden im Rahmen dieser Arbeit erstmals erfolgreich auf ihre aktiven optischen Eigenschaften hin untersucht. Sie zeigen eine optische Emission zwischen 1,9 und 2 eV im sichtbaren Bereich. Diese strahlende Rekombination wird ebenfalls dem direkten Übergang zwischen Elektronen- und Löcherzuständen zugeordnet, die in den InP Quantenpunkten lokalisiert sind. Auch Photolumineszenzmessungen unter mechanischem Druck weisen darauf hin, dass es sich in diesem System hauptsächlich um einen direkten räumlichen Übergang handelt. Dieses Ergebnis wird dadurch untermauert, dass die Lebensdauer der Ladungsträger im Bereich von etwa 2 ns liegt, was nicht untypisch für Typ-I-Systeme ist. Die Ergebnisse für zweidimensionale, in GaP eingebettete InP-Schichten zeigen im Gegensatz zu den Quantenpunkten, dass die strahlende Rekombination in InP/GaP Quantentöpfen aufgrund eines indirekten Übergangs (sowohl in Orts- als auch in Impulsraum) zwischen Elektronen- und Löcherzuständen erfolgt. Die optischen Emissionslinien liegen für Quantentöpfe im Bereich von 2,15 bis 2,30eV. Die nachgewiesene sehr lange Lebensdauer der Ladungsträger von etwa 20ns weist weiter darauf hin, dass die Quantentöpfe ein Typ-II-System sind. Nach Modellierung des Bänderschemas für das verspannte InP/GaP-System und Berechnung der Energieniveaus von Löchern und Elektronen darin mit Hilfe der Effektive-Masse-Näherung in Abhängigkeit von der InP-Schichtdicke zeigt sich ferner, dass für InP-Quantentöpfe mit einer Breite kleiner als 3nm die Quantisierungsenergie der Elektronen so groß ist, dass der X-Punkt in GaP energetisch tiefer liegt als der Gamma-Punkt in InP. Dieser Potentialverlauf führt dazu , dass die Elektronen im X-Minimum des GaP lokalisieren, während die Löcher in der InP-Schicht bleiben. Optische Untersuchungen nach thermischer Behandlung der Quantenpunkte führen sowohl im InP/InGaP- als auch im InP/GaP-System zur Verstärkung der Lumineszenz, die bis zu 15 mal internsiver als bei unbehandelten Proben sein kann. Insgesamt zeigt diese Arbeit, dass InP-Quantenpunkte durch ihre optischen Eigenschaften sehr interessant für optoelektronische Anwendungen sind. Die Verwendung von durchsichtigem GaP (mit einer größeren Bandlücke und kleineren Gitterkonstante im Vergleich zu GaAs und InGaP) als Matrix und Substrat hat nicht nur den Vorteil, dass die InP-Quantenpunkte hierbei im sichtbaren Bereich Licht emittieren, sondern man kann in der Praxis auch von einer hochentwickelten GaP-basierten LED-Technologie profitieren. Hauptergebnis dieser Arbeit ist, dass die in indirektes GaP eingebetteten InP-Quantenpunkte aktive optische Eigenschaften zeigen. Sie können daher als aktive Medien zur Realisierung neuartiger effizienter Laser und Leuchtdioden verwendet werden.The growth and structural properties of self-assembled InP quantum dots are presented and discussed, together with their optical properties and associated carrier dynamics. The QDs are grown using gas-source molecular-beam epitaxy in and on the two materials InGaP (lattice matched to GaAs) and GaP. Under the proper growth conditions, formation of InP dots via the Stranski-Krastanow mechanism is observed. The critical InP coverage for 2D-3D transition is found to be 3ML for the InP/ InGaP system and 1.8ML for the InP/GaP system. The structural characterization indicates that the InP/GaP QDs are larger and, consequently, less dense compared to the InP/ InGaP QDs; hence, InP dots on GaP tend to be strain-relaxed. The InP/ InGaP QDs tend to form ordered arrays when InP coverage is increased. Intense photoluminescence from InP quantum dots in both material systems is observed. The PL from InP/GaP QDs peaks between 1.9 and 2 eV and is by about 200 meV higher in energy than the PL line from InP/ InGaP QDs. The optical emission from dots is attributed to direct transitions between the electrons and heavy-holes confined in the InP dots, whereas the photoluminescence from a two-dimensional InP layer embedded in GaP is explained as resulting from the spatially indirect recombination of electrons from the GaP X valleys with holes in InP and their phonon replicas. The type-II band alignment of InP/GaP two-dimensional structures is further confirmed by the carrier lifetime above 19 ns, which is much higher than in type-I systems. The observed carrier lifetimes of 100-500 ps for InP/ InGaPQDs and 2 ns for InP/GaP QDs support our band alignment modeling. Pressure-dependent photoluminescence measurements provide further evidence for a type-I band alignment for InP/GaP QDs at normal pressure, but indicate that they become type-II under hydrostatic pressures of about 1.2 GPa and are consistent with an energy difference between the lowest InP and GaP states of about 31 meV. Exploiting the visible direct-bandgap transition in the GaP system could lead to an increased efficiency of light emission in GaP-based light emitters.
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Shahid, Naeem. "Technology and properties of InP-based photonic crystal structures and devices." Doctoral thesis, KTH, Halvledarmaterial, HMA, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-101662.
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Photonic crystals (PhCs) are periodic dielectric structures that exhibit a photonic band gap; a range of wavelengths for which light propagation is forbidden. 2D PhCs exhibit most of the properties as their three dimension counterparts with a compatibility with standard semiconductor processing techniques such as epitaxial growth, electron beam lithography, Plasma deposition/etching and electromechanical lapping/polishing. Indium Phosphide (InP) is the material of choice for photonic devices especially when it comes to realization of coherent light source at 1.55 μm wavelength. Precise engineering of the nanostructures in the PhC lattice offers novel ways to confine, guide and control light in phonic integrated circuits (PICs). Strong confinement of light in PhCs offer novel opportunities in many areas of physics and engineering. Dry etching, a necessary process step in PhC device manufacturing, is known to introduce damage in the etched material. Process induced damage and its impact on the electrical and optical properties of PhCs depends on the etched material, the etching technique and process parameters. We have demonstrated a novel post-etch process based on so-called mass-transport (MT) technology for the first time on InP-based PhCs that has significantly improved side-wall verticality of etched PhC holes. A statistical analysis performed on several devices fabricated by MT process technology shows a great deal of improvement in the reliability of optical transmission characteristics which is very promising for achieving high optical quality in PhC components. Several PhC devices were manufactured using MT technology. Broad enough PhC waveguides that operate in the mono/multi-mode regime are interesting for coarse wavelength de-multiplexing. The fundamental mode and higher order mode interaction creates mini-stop band (MSB) in the dispersion diagram where the higher order mode has a lower group velocity which can be considered as slow light regime. In this thesis work, the phenomena of MSBs and its impact on transmission properties have been evaluated. We have proposed and demonstrated a method that enables spectral tuning with sub-nanometer accuracy which is based on the transmission MSB. Along the same lines most of the thesis work relates to broad enough PhC guides that operated in the multimode regime. Temperature tuning experiments on these waveguides reveals a clear red-shift with a gradient of dλ/dT=0.1 nm/˚C. MSBs in these waveguides have been studied by varying the width in incremental amounts. Analogous to semiconductors heterostructures, photonic heterostructures are composed of two photonic crystals with different band-gaps obtained either by changing the air-fill factor or by the lattice constant. Juxtaposing two PhC and the use of heterostructures in waveguide geometry has been experimentally investigated in this thesis work. In particular, in multimode line defect waveguides the “internal” MSB effect brings a new dimension in single junction-type photonic crystal waveguide (JPCW) and heterostructure W3 (HW3) for fundamental physics and applications. We have also fabricated an ultra-compact polarization beam splitter (PBS) realized by combining a multimode waveguide with internal PhC. MSBs in heterostructure waveguides have shown interesting applications such as designable band-pass flat-top filters, and resonance-like filters with high transmission. In the course of this work, InGaAsP suspended membrane technology was developed. An H2 cavity with a linewidth of ~0.4 nm, corresponding to a Q value of ~3675 has been shown. InGaAsP PhC membrane is an ideal platform to study coupled quantum well/dot-nanocavity system.QC 20120831
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Kristukat, Christian. "High pressure study of the electronic structure of self-assembled InAs/GaAs and InP/GaP quantum dots." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=97877339X.
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BENSAOULA, ABDELHAKIM. "Realisation d'un super-reseau a contraintes balancees inp/gaas/gap/gaas par epitaxie par jets moleculaires d'organo-metalliques." Nice, 1995. http://www.theses.fr/1995NICE4857.
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Les premiers travaux portant sur les effets des contraintes sur les proprietes des semi-conducteurs remontent a plus de 30 ans. Aujourd'hui, l'utilisation des contraintes comme parametres ajustables permettant la modification des proprietes electroniques des materiaux est largement acceptee. Cependant, l'application experimentale de ce phenomene rencontre bien des difficultes. En effet, les materiaux contraints se trouvent aussi predisposes aux defauts de dislocations de par la limite imposee par l'epaisseur critique. Dans ce travail, nous proposons l'utilisation de super-reseaux a contraintes alternees afin de contourner ce probleme. Depose sur du gaas (100), gap presente un desaccord de maille de -3,7% quant a inp, depose sous les memes conditions, il presente un desaccord de maille de +3,9%. Ces valeurs font du super-reseau gap/gaas/inp/gaas le parfait exemple permettant une meilleure comprehension des phenomenes mis en jeux. Nous etudions, dans un premier temps, les structures simples gap/gaas et inp/gaas en preparation a l'etude des structures plus complexes. Les resultats obtenus par diffraction des rayons-x et spectroscopie de photoluminescence montrent un parfait accord entre les niveaux des contraintes mesures et les energies du gap. Nous montrons qu'il est possible, par un choix des epaisseurs des couches de gap et inp, de deplacer la reponse optique de la structure sur une large region d'energie
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Auvray, Laurent. "EPVOM du matériau InGaAs-InP avec l'arsine ou le triméthylarsenic et du nitrure à petit gap GaAsN-GaAs : utilisation de l'azote comme gaz vecteur." Lyon 1, 2001. http://www.theses.fr/2001LYO19001.
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Les matériaux InGaAs et GaAsN ont été élaborés par EPVOM en utilisant comme gaz vecteur H2 ou N2. Un inconvénient de l'EPVOM est l'utilisation d'hydrures (arsine, phosphine) très toxiques, stockés sous haute pression. Par contre le triméthylarsenic (TMAs) est un composé peu toxique, liquide à température ambiante. Nous présentons une étude comparative entre le TMAs et l'arsine pour la croissance de In0,53Ga0,47As/InP, en association avec le triméthylindium et le triméthylgallium (TMG). La substitution du TMAs à l'arsine induit une dégradation des propriétés morphologiques (AFM), électriques et optiques des couches, tendance dramatiquement accentuée sous gaz vecteur N2. En revanche, avec l'arsine, des couches de qualité électronique équivalente sont obtenues avec H2 ou N2. Les nitrures Ga(In)AsN s'imposent aujourd'hui comme une voie pour réaliser l'émission à 1,3 micromètre sur substrat GaAs. Cette longueur d'onde, utile pour les Télécommunications optiques, est accessible car l'incorporation de faibles quantités d'azote réduit fortement le gap du matériau. Cependant, cette incorporation est difficile est nécessite des conditions de croissance fortement hors-équilibre. Nous avons privilégié le gaz vecteur N2 car il facilite cette incorporation. La 1,1-diméthylhydrazine a été choisie comme précurseur de l'azote, associée au TGM et à l'arsine. L'incorporation de l'azote a été étudiée en fonction des paramètres de croissance. Son influence sur le mode de croissance des couches a été explorée. Les propriétés optiques ont été caractérisées par photoluminescence (PL) et par photoréflectivité. L'incorporation d'azote dégrade fortement la luminescence du matériau. Cependant, un recuit post-croissance des couches, dans des conditions optimisées, permet une amélioration spectaculaire de leur qualité optique. L'émission de PL à basse température a pour origine la recombinaison d'excitons localisés. À plus haute température, elle est dominée par la recombinaison d'excitons libres.
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Shao, Jun. "Effective mass and valence-band structure in Ga Kappa In 1-Kappa As/InP and Ga Kappa In 1-Kappa P/AlGaInP quantum wells." [S.l. : s.n.], 2002. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9818580.
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Braccioli, Marco <1979>. "Study of silicon-on-insulator multiple-gate MOS structures including band-gap engineering and self heating effects." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1515/.
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The progresses of electron devices integration have proceeded for more than 40 years following the well–known Moore’s law, which states that the transistors density on chip doubles every 24 months. This trend has been possible due to the downsizing of the MOSFET dimensions (scaling); however, new issues and new challenges are arising, and the conventional ”bulk” architecture is becoming inadequate in order to face them.
In order to overcome the limitations related to conventional structures, the researchers
community is preparing different solutions, that need to be assessed.
Possible solutions currently under scrutiny are represented by:
• devices incorporating materials with properties different from those of silicon, for
the channel and the source/drain regions;
• new architectures as Silicon–On–Insulator (SOI) transistors: the body thickness of Ultra-Thin-Body SOI devices is a new design parameter, and it permits
to keep under control Short–Channel–Effects without adopting high
doping level in the channel.
Among the solutions proposed in order to overcome the difficulties related to scaling,
we can highlight heterojunctions at the channel edge, obtained by adopting for the
source/drain regions materials with band–gap different from that of the channel material.
This solution allows to increase the injection velocity of the particles travelling
from the source into the channel, and therefore increase the performance of the transistor
in terms of provided drain current.
The first part of this thesis work addresses the use of heterojunctions in SOI transistors:
chapter 3 outlines the basics of the heterojunctions theory and the adoption of such
approach in older technologies as the heterojunction–bipolar–transistors; moreover the
modifications introduced in the Monte Carlo code in order to simulate conduction band
discontinuities are described, and the simulations performed on unidimensional simplified
structures in order to validate them as well.
Chapter 4 presents the results obtained from the Monte Carlo simulations performed
on double–gate SOI transistors featuring conduction band offsets between the source
and drain regions and the channel. In particular, attention has been focused on the drain
current and to internal quantities as inversion charge, potential energy and carrier velocities.
Both graded and abrupt discontinuities have been considered.
The scaling of devices dimensions and the adoption of innovative architectures have
consequences on the power dissipation as well. In SOI technologies the channel is thermally
insulated from the underlying substrate by a SiO2 buried–oxide layer; this SiO2
layer features a thermal conductivity that is two orders of magnitude lower than the
silicon one, and it impedes the dissipation of the heat generated in the active region.
Moreover, the thermal conductivity of thin semiconductor films is much lower than
that of silicon bulk, due to phonon confinement and boundary scattering. All these aspects
cause severe self–heating effects, that detrimentally impact the carrier mobility
and therefore the saturation drive current for high–performance transistors; as a consequence,
thermal device design is becoming a fundamental part of integrated circuit
engineering.
The second part of this thesis discusses the problem of self–heating in SOI transistors.
Chapter 5 describes the causes of heat generation and dissipation in SOI devices, and
it provides a brief overview on the methods that have been proposed in order to model
these phenomena. In order to understand how this problem impacts the performance of
different SOI architectures, three–dimensional electro–thermal simulations have been
applied to the analysis of SHE in planar single and double–gate SOI transistors as well
as FinFET, featuring the same isothermal electrical characteristics.
In chapter 6 the same simulation approach is extensively employed to study the impact
of SHE on the performance of a FinFET representative of the high–performance
transistor of the 45 nm technology node. Its effects on the ON–current, the maximum
temperatures reached inside the device and the thermal resistance associated to the device
itself, as well as the dependence of SHE on the main geometrical parameters have
been analyzed. Furthermore, the consequences on self–heating of technological solutions
such as raised S/D extensions regions or reduction of fin height are explored as
well.
Finally, conclusions are drawn in chapter 7.
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Niessen, Daniel <1983>. "Nonlinear Characterization and Modelling of GaN HEMTs for Microwave Power Amplifier Applications." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5774/.
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Semiconductors technologies are rapidly evolving driven by the need for higher
performance demanded by applications. Thanks to the numerous advantages that
it offers, gallium nitride (GaN) is quickly becoming the technology of reference
in the field of power amplification at high frequency. The RF power density of
AlGaN/GaN HEMTs (High Electron Mobility Transistor) is an order of magnitude
higher than the one of gallium arsenide (GaAs) transistors. The first demonstration
of GaN devices dates back only to 1993. Although over the past few years some
commercial products have started to be available, the development of a new
technology is a long process. The technology of AlGaN/GaN HEMT is not yet
fully mature, some issues related to dispersive phenomena and also to reliability
are still present. Dispersive phenomena, also referred as long-term memory effects,
have a detrimental impact on RF performances and are due both to the presence
of traps in the device structure and to self-heating effects. A better understanding
of these problems is needed to further improve the obtainable performances.
Moreover, new models of devices that take into consideration these effects are
necessary for accurate circuit designs. New characterization techniques are thus
needed both to gain insight into these problems and improve the technology and
to develop more accurate device models.
This thesis presents the research conducted on the development of new charac-
terization and modelling methodologies for GaN-based devices and on the use of
this technology for high frequency power amplifier applications.
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D’Angelo, Sara <1980>. "Electrothermal characterization and nonlinear modelling of GaN transistors for telecommunication circuit design." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3665/.
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This thesis starts showing the main characteristics and application fields of the AlGaN/GaN HEMT technology, focusing on reliability aspects essentially due to the presence of low frequency dispersive phenomena which limit in several ways the microwave performance of this kind of devices. Based on an equivalent voltage approach, a new low frequency device model is presented where the dynamic nonlinearity of the trapping effect is taken into account for the first time allowing considerable improvements in the prediction of very important quantities for the design of power amplifier such as power added efficiency, dissipated power and internal device temperature. An innovative and low-cost measurement setup for the characterization of the device under low-frequency large-amplitude sinusoidal excitation is also presented. This setup allows the identification of the new low frequency model through suitable procedures explained in detail.
In this thesis a new non-invasive empirical method for compact electrothermal modeling and thermal resistance extraction is also described. The new contribution of the proposed approach concerns the non linear dependence of the channel temperature on the dissipated power. This is very important for GaN devices since they are capable of operating at relatively high temperatures with high power densities and the dependence of the thermal resistance on the temperature is quite relevant.
Finally a novel method for the device thermal simulation is investigated: based on the analytical solution of the tree-dimensional heat equation, a Visual Basic program has been developed to estimate, in real time, the temperature distribution on the hottest surface of planar multilayer structures. The developed solver is particularly useful for peak temperature estimation at the design stage when critical decisions about circuit design and packaging have to be made. It facilitates the layout optimization and reliability improvement, allowing the correct choice of the device geometry and configuration to achieve the best possible thermal performance.
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Stevenson, Angela. "Bridging the Gap: Transition from Collegiate IEP Writing Courses to First-Year Writing Courses." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1591777977234548.
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Saxena, Himanshu. "Tunable Terahertz Detectors Based on Plasmon Exciation in Two Dimensional Electron Gasses in InGaAs/InP and AlGaN/GaN HEMT." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3924.
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The observation of voltage-tunable plasmon resonances in the terahertz range in two dimensional electron gas (2-deg) of a high electron mobility transistor (HEMT) fabricated from the InGaAs/InP and AlGaN/GaN materials systems is reported. The devices were fabricated from a commercial HEMT wafer by depositing source and drain contacts using standard photolithography process and a semi-transparent gate contact that consisted of a 0.5 [micro]m period transmission grating formed by electron-beam lithography. Narrow-band resonant absorption of THz radiation was observed in transmission in the frequency range 10-100 cm-1. The resonance frequency depends on the gate voltage-tuned sheet-charge density of the 2deg. The fundamental and higher resonant harmonics were observed to shift towards lower frequencies with the implementation of negative gate bias. The theory of interaction of sub millimeter waves with 2deg through corrugated structure on top has been applied to calculate and understand the phenomena of resonant plasmon excitations. The observed separation of resonance fundamental from its harmonics and their shift with gate bias follows theory, although the absolute frequencies are lower by about a factor of 2-3 in InGaAs/InP system. However, calculated values match much better with AlGaN/GaN system.Ph.D.
Department of Physics
Sciences
Physics PhD
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Penner, Jakob. "Lokale Gitterumgebung von Indium in GaN, AlN und InN." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985159979.
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Merrill, Ky. "OPTICAL ANISOTROPY IN InN/GaN DISK-IN-WIRE STRUCTURES." OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/886.
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In this work, we use valence force-field mechanics, sp3d5s* tight-binding models, and an array of post-processing tools to study the anisotropy in the optical polarization of a GaN/InN/GaN disk-in-wire structure. These types of systems possess an underlying Wurtzite crystal lattice structure, which results in the formation of pyro-electric fields in addition to the piezoelectric fields that arise due to mechanical stress in the form of strain on the crystal lattice. This family of nanostructures is important for three reasons: 1) Strain relaxation allows for design freedom in terms of lattice and energy band matching; 2) Using a larger indium content, with the benefit of fewer strain induced effects due to relaxation, allows for the possibility of full-spectrum LED's and solar cells; 3) They display higher temperature stability of threshold current and luminescence than currently employed technologies.
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Herbeaux, Christian. "Étude par microscopie électronique en transmission des défauts structuraux induits par les contraintes dans les hétérostructures Ga1-xInxAs/InP et Ga1-xInxAs/GaAs." Lille 1, 1990. http://www.theses.fr/1990LIL10043.
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Cette étude est centrée sur une analyse par microscopie électronique en transmission des défauts structuraux associés à la croissance épitaxiale du matériau semiconducteur GA1-xInxAs sur substrat InP ou sur substrat GaAq, ces deux types de supports correspondants aux deux filières classiques de croissance de cet alliage ternaire. L'objectif principal a été l'étude des propriétés structurales des dislocations de désadaptation de réseau et des mécanismes par lesquels ces dislocations relâchent tout ou partie des contraintes générées lors de l'épitaxie. Ces mécanismes concernent à la fois la génération et la multiplication de ces dislocations. Dans le cas du matériau GA1-xInxAs pratiquement adapté au matériau InP, le critère de pseudomorphisme est presque toujours satisfait, même pour des épaisseurs importantes de la couche épitaxiée. La densité de dislocations de désadaptation de réseau restant faible, on peut alors mettre en évidence des effets plus fins liés à la présence de fluctuations de composition au niveau des interfaces. Les structures Ga1-xInxAs/GaAs contraintes, choisies comme modèles d'étude, nous ont permis de mettre en évidence et d'interpréter la nature des dislocations et de leurs interactions, tout en tenant compte de leur caractère dissocié. Nous montrons que les modèles habituellement invoqués pour interpréter la multiplication des dislocations aux interfaces ne peuvent pas rendre compte de nos observations. Enfin, l'analyse des micrographies électroniques permet de proposer un mécanisme de source de type Frank-Read basé sur le glissement dévié des segments vis, mécanisme qui pourrait être à l'origine de la multiplication des dislocations de désadaptation dans ce type d'hétérostructure
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吳誼暉 and Yee-fai Ng. "Heteroepitaxial growth of InN on GaN by molecular beam epitaxy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B29797846.
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Ng, Yee-fai. "Heteroepitaxial growth of InN on GaN by molecular beam epitaxy /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25212175.
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Tu, Chia-Wei. "Reflective Properties and Lasing of InP Photonic Crystals and Frequency Doubling in GaMnN Thin Films." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627660467940462.
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Saxena, Himanshu. "Tunable terahertz detectors based on plasmon exciation in two dimensional electron gases in InGaAs/InP and AlGaN/GaN HEMT." Orlando, Fla. : University of Central Florida, 2009. http://purl.fcla.edu/fcla/etd/CFE0002912.
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Layati, Bouchta. "Croissance par épitaxie par jets moléculaires d'hétérostructures AlInAs/Ga1-xInxAs/InP à dopage planaire pour application aux transistors HEMT." Lille 1, 1996. http://www.theses.fr/1996LIL10167.
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Cette thèse a pour objet l'étude de la croissance par épitaxie par jets moléculaires des matériaux al0. 48in0. 52as / ga1-xinxas pour la réalisation d'hétérostructures sur substrat InP. La couche active de GaInAs est épitaxiée en adaptation de maille ou contrainte en compression sur le substrat. Un travail de caractérisation basée sur des méthodes physiques et électriques a défini les conditions de croissance de ces structures pour l'application au transistor HEMT. Dans ces épitaxies multicouches la détermination précise de la densité d'électrons libres ns et de la mobilité électronique qui sont associées à chaque couche est obtenue à partir d'une exploitation originale des mesures électriques. L'avantage du dopage planaire par rapport au dopage volumique est vérifié par l'obtention d'un produit plus élevé ns x dans le gaz bidimensionnel formé à l'interface AlInAs / GaInAs. L'utilisation du plan de dopage est étudiée dans le cas de l'interface avant (couche active placée entre le substrat et la couche donneuse) et dans le cas de l'interface arrière (couche active placée entre la couche donneuse et la surface). Grâce à l'optimisation des paramètres de croissance, les performances des hétérostructures épitaxiées sont d'un niveau élevé (ns de 3 10#1#2 cm-2 et une mobilité de 42000 cm2/vs dans le gaz pour une structure comprenant un dopage planaire avant de 5 10#1#2 cm-2 et une couche active contrainte à 75% d'indium). L'association des deux types d'interface au niveau de la même couche active de GaInAs permet d'augmenter de manière importante la densité d'électrons transférée dans le gaz en gardant une mobilité électronique élevée (ns de 6 10#1#2 cm-2 et de 31000 cm2/vs avec un dopage arrière de 3 10#1#2 cm-2, un dopage avant de 5 10#1#2 cm-2 et une couche active contrainte à 70%). Enfin des transistors HEMT à grille submicronique réalisés à partir des couches épitaxiées ont été caractérisés en statique et dans le domaine des hyperfréquences. Les très bonnes performances obtenues (courant drain de 1 a/mm, fmax de 300 GHz, facteur de bruit inférieur à 0. 8db) confirment le choix des conditions de croissance
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Trassaert, Stéphane. "Réalisation technologique de transistors à effet de champ dans les filières InP et GaN pour amplification de puissance hyperfréquence." Lille 1, 2000. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2000/50376-2000-45.pdf.
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Ce travail porte sur la realisation de transistors a effet de champ dans les deux filieres de semiconducteurs inp et gan pour l'amplification de puissance hyperfrequences. La premiere partie est consacree a la realisation en technologie microruban d'elements passifs et actifs afin de concevoir un circuit de puissance a 60 ghz sur substrat d'inp. Une technologie originale de trous metallises a ete mise au point par voie chimique. Des elements passifs ont ete realises avec cette technologie et mesures en hyperfrequences afin de valider ou completer les modeles de la bibliotheque du simulateur mds. Des hemts ont ete realises en technologies microruban et coplanaire. L'analyse de leurs caracteristiques electriques n'a montre aucune degradation apportee par les trous metallises. Nous disposons ainsi de tous les elements necessaires a la realisation du circuit d'amplificationLa seconde partie porte sur la realisation de mesfets dans la filiere gan pour des applications en puissance et a haute temperature. Les differentes briques technologiques permettant de realiser le composant ont ete d'abord etudiees. Le contact ohmique retenu tient thermiquement jusqu'a 600\c. Une gravure du gan par plasma a aussi ete mise au point. Enfin, le contact schottky a ete aborde. Les composants realises ont ete caracterises. Nous avons obtenu, selon la distance source drain, jusqu'a 140 v et 350 v pour respectivement une tenue en tension vds en configuration transistor a canal ouvert et une tension de claquage en configuration diode inverse. La mesure a haute temperature a montre le fonctionnement du composant jusqu'a 450\c sans degradation. La mesure en regime impulsionnel a mis en evidence l'existence de pieges localises en surface qui peuvent etre excites par la lumiere et/ou la temperature et/ou le point de polarisation. Une densite de puissance de 2,2 w/mm a ete obtenue a 3 ghz pour une longueur de grille de 300 nm, ce qui constitue un resultat au niveau de l'etat de l'art
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Dessenne, François. "Etude théorique et optimisation de transistors à effet de champ de la filière InP et de la filière GaN." Lille 1, 1998. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1998/50376-1998-19.pdf.
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Notre etude contribue a l'analyse du fonctionnement physique des transistors a effet de champ par la methode de monte carlo. Notre but est de presenter des ameliorations aux concepteurs dans les domaines de l'amplification faible bruit en gamme millimetrique d'une part et de l'amplification de puissance d'autre part. Dans le premier chapitre, apres avoir passe en revue les differentes possibilites de transistors a effet de champ capables de satisfaire a notre cahier des charges, nous estimons leurs potentialites et leurs limitations respectives. Les chapitres ii et iii nous permettent de decrire notre programme de simulation du transport de charges dans les semi-conducteurs massifs et dans les dispositifs destines a l'hyperfrequence. Pour la filiere inp, le simulateur a ete adapte a la modelisation de hemt (high electron mobility transistor) a grille largement submicronique et presentant des discontinuites de bande elevees. Dans le quatrieme chapitre, nous menons l'examen des performances de hemt al0. 48in0. 52as/ga0. 47in0. 53as/inp destines a l'amplification faible bruit a 60 et 94 ghz, tant sur le plan theorique que sur le plan experimental. Il apparait clairement que la presence d'ionisation par choc dans le canal de ces transistors degrade de maniere importante leurs caracteristiques hyperfrequences. Afin d'optimiser ces composants, plusieurs solutions sont alors proposees avec un avantage pour l'utilisation d'un canal composite gainas/inp. La realisation de lmhemt avec ce type de canal confirme nos predictions en offrant une elevation du gain intrinseque en tension de plus de 60% dans le cas d'un canal avec une couche d'inp dope, par rapport a la structure conventionnelle.
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Potthoff, Anna-Laura [Verfasser]. "Auswirkungen einer pharmakologischen Inhibition von Gap Junctions durch INI-0602 auf die Therapie des Glioblastoms / Anna-Laura Potthoff." Bonn : Universitäts- und Landesbibliothek Bonn, 2021. http://d-nb.info/1240761244/34.
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Loewens, Sofia. "Entwicklungsorganisation und -prozesse für Multibrandstrategien an ausgewählten Beispielen." St. Gallen, 2005. http://www.biblio.unisg.ch/org/biblio/edoc.nsf/wwwDisplayIdentifier/02605343001/$FILE/02605343001.pdf.
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Lawhon, Stanley Ray. "Team building bridging the leadership gap between the staff and eldership of Eastside Christian Church /." Theological Research Exchange Network (TREN), 2002. http://www.tren.com.
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Wang, Jielei Ms. "Optical Properties of In1-xGaxN Epilayers Grown by HPCVD." Digital Archive @ GSU, 2010. http://digitalarchive.gsu.edu/phy_astr_theses/9.
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Optical absorption spectroscopy has been applied to study properties such as the fundamental absorption edge and defect absorption centers of group III-nitride compound semiconductor epilayers. The investigation in this thesis focused on analyzing the band gap of indium-rich In1-xGaxN epilayers, which where grown by the high-pressure chemical vapor deposition (HPCVD) technique. Our results - together with literature data for gallium-rich In1-xGaxN alloys indicate that the shift of the fundamental band gap of In1-xGaxN with composition x can be described with a bowing parameter of b = 2.2eV. Temperature dependent transmission measurements show that the band gap variation with temperature follows a S-shape behavior for small gallium concentration and shifts towards a Varshni type behavior for a higher gallium concentrations. The S-shape behavior is attributed to nanoscale compositional fluctuations/clustering in the ternary alloy system. The thicknesses of the measured In1-xGaxN epilayers have been analyzed through multilayer stack model calculations of the transmission spectra. The free electron concentration in the In1-xGaxN epilayers has been obtained from simulations of infrared reflectance spectra.
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Winnubst, Patrick. "REPORT OF AN INTERNSHIP WITH ENSR|AECOM INC. SEPTEMBER 2006 TO SEPTEMBER 2007." Miami University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=miami1229032333.
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Ford, Michael John. "Fundamental studies of mixed gas plasmas in ICP-MS." Thesis, University of Plymouth, 1993. http://hdl.handle.net/10026.1/1941.
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Inductively coupled plasma - mass spectrometry is widely accepted as the leading technique for trace element analysis. It suffers however, from a range of interferences both spectral and non - spectral which limit the range of analytes and substrates which may be successfully analyzed. This study has investigated the use of mixed gas plasmas as a means of reducing or removing these interference effects. In addition the use of mixed gas plasmas for sensitivity enhancement has been assessed using both wet and dry sample introduction systems. Simplex optimization procedures have been used throughout. The addition of nitrogen to all three argon gas flows of the ICP was evaluated, and the instrumental operating conditions were optimized to allow for the maximum removal of the ArCl+ interference on As and Se. The addition of nitrogen to the nebulizer gas was particularly effective in the removal of the ArCl+. The use of nitrogen addition also facilitated the determination of arsenic in samples where it was previously found to be impossible. The addition of methane was also applied to all three gas flows of the ICP, however, in this case only the addition to the nebulizer gas was successful in removing interferences. These included ArO+, ClO+ and CeO+ in addition to ArCl+ . Detection limits, recoveries and CRM analysis were all improved by the use of methane addition when compared to nitrogen addition or standard argon plasmas. Hydrogen addition was applied solely to the nebulizer gas and found to significantly increase the magnitude of the interferences from argon based polyatomic ions, whilst reducing those from metal oxides. The addition of hydrogen was useful in reducing MO+ interferences, but the removal of other interferences proved unsuccessful. The addition of ethene to the nebulizer gas has been used to remove many of the polyatomic interferences encountered in ICP-MS, including those based on Na, S and P. Ethene addition was as effective as, and usually better than, the addition of both methane and nitrogen. Detection limits, recoveries, calibrations and CRM analysis were all improved by its use. The use of ethene addition has lead to improvement in the determination of As, Cu, Fe, Gd, Ni, Se, and V in the presence of the relevant interference precursors. Most importantly it has been shown that a whole range of interferences can be reduced simultaneously with the addition of ethene. The plasma operating parameters and ion optics settings of a commercial ICP-MS instrument were optimized to yield maximum SBRs for elements across the mass range. It was shown that simple manual tuning of the instrument did not effect the SBRs, when compared to the simplex optimized conditions. Finally it was shown that the addition of molecular gases to the ICP, did not result in any significant improvements in sensitivity, when compared to the all argon system. Finally it has been shown that the addition of a relatively small amount of hydrogen to the nebulizer gas can lead to an enhancement in the signal obtained using laser ablation sampling. This enhancement was greatest for low mass elements and had no effect on the heavy mass element signal.
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Müller, Sabine, Veronika Safarova, and Michelle Villavicencio. "Analysing the Communication Gap in a Business-to-Business Setting : A Qualitative Study of Alpha Inc. Sweden and its After Sales Service." Thesis, Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-25335.
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Drouot, Virginie. "Elaboration par épitaxie par jets moléculaires et caractérisation d'hétérostructures pseudomorphiques Ga1-xInxAs/AlInAs sur InP pour transistors à haute mobilité d'électron (HEMT)." Ecully, Ecole centrale de Lyon, 1993. http://www.theses.fr/1993ECDL0035.
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LES TRANSISTORS A HAUTE MOBILITE D'ELECTRON SONT TRES ATTRACTIFS POUR LA REALISATION DE DISPOSITIFS HYPERFREQUENCES DANS LE DOMAINE DE L'AMPLIFICATION FAIBLE BRUIT. LE SYSTEME Ga1-xInxAs/AlInAs SUR InP POSSEDE DE GRANDES POTENTIALITES POUR LA REALISATION DE CES COMPOSANTS ULTRA-RAPIDES: TRES FORTE MOBILITE DES ELECTRONS DANS GAINAS ET GRANDE DISCONTINUITE DES BANDES DE CONDUCTION ENTRE GaInAs ET AlInAs. L'UTILISATION DANS LE CANAL D'UN ALLIAGE DE Ga1-xInxAs PLUS RICHE EN INDIUM QUE CELUI CORRESPONDANT A L'ACCORD DE MAILLE (x=0,53) AMELIORE LES PROPRIETES ELECTRONIQUES DE L'HETEROSTRUCTURE (TRANSFERT ET MOBILITE DES ELECTRONS). L'ESSENTIEL DE CE TRAVAIL A PORTE SUR LA DEFINITION DES CONDITIONS DE CROISSANCE D'HETEROSTRUCTURES A CANAL DE Ga1-xInxAs AVEC UNE COMPOSITION xIn LA PLUS ELEVEE POSSIBLE. NOUS AVONS ELABORE DES HETEROSTRUCTURES PSEUDOMORPHIQUES A MODULATION DE DOPAGE Ga1-xInxAs/AlInAs SUR InP, PAR EPITAXIE PAR JETS MOLECULAIRES EN BALAYANT UNE LARGE GAMME DE COMPOSITIONS ET DE TEMPERATURES DE CROISSANCE. LES MEILLEURES CARACTERISTIQUES ELECTRIQUES DETERMINEES PAR EFFET HALL ONT ETE OBTENUES POUR UNE COMPOSITION X=0,75 ET UNE TEMPERATURE DE CROISSANCE Tc=500°C. UNE CORRELATION ETROITE ENTRE LES CONDITIONS DE CROISSANCE ET LES PROPRIETES OPTIQUES ET ELECTRIQUES DES STRUCTURES CONTRAINTES A ETE EFFECTUEE. DES CONDITIONS DE CROISSANCE OPTIMISEES, CONDUISANT A DES CINETIQUES DE SURFACE ELEVEES, NOUS ONT PERMIS D'AMELIORER L'ORDRE STRUCTURAL DE LA COUCHE CONTRAINTE ET DE DIMINUER LA RUGOSITE DES INTERFACES. DES STRUCTURES SPECIFIQUES ONT ETE REALISEES POUR FABRIQUER DES TRANSISTORS HEMT POUR DIFFERENTES COMPOSITIONS EN INDIUM DU CANAL. LA TRANSCONDUCTANCE DE TRANSISTORS D'UNE LONGUEUR DE GRILLE DE 4 um AUGMENTE DE 100 A 210 mS/mm LORSQUE LA COMPOSITION EN INDIUM DANS LE CANAL AUGMENTE DE 53 A 75%
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Johansson, Anna, Marie Nolander, and Petra Waldemar. "An Interpretation of the Financial Gap : Practical versus Analytical Reasoning." Thesis, Jönköping University, JIBS, Accounting and Finance, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-11360.
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Abstract
Background: Small businesses are vital for the welfare of a country. Yet, they have trou-ble obtaining external financing and these difficulties are gathered under the umbrella concept the “Financial Gap”. The most common source of fund-ing for small businesses is bank loan, why the availability of bank financing is a critical factor for their success. Today, 31% of all Swedish companies argue that they have finance problems and for half of these, the problem is to obtain a bank loan.
Purpose: The purpose of the study is to describe and explain the Financial Gap as a relational concept. That is to say that the study will contribute to the understanding of the Financial Gap by focusing on the perspectives of both small businesses and banks interactively.
Method: The study views the concept of the Financial Gap from a practical stand-point, assuming that it expresses its existence in the interaction between small businesses and banks. To pursue this view, the study takes on an Eth-nomethodological research approach. This approach is necessary in order to come close to and understand small businesses‟ and banks‟ everyday prac-tises. In-depth interviews are used for obtaining this deeper understanding of both parties. In addition, a questionnaire was sent out to small businesses in order to verify the information gathered in the interviews.
Conclusion: On the basis of the study, the authors have developed an Interactive Model which describes their understanding of the Financial Gap. The members of small businesses and banks deal with information differently, which in turn is a result of how they approach ambiguity. When ambiguity is present, small firms settle with making decisions under uncertainty, whereas banks prefer to calculate on probabilities, why their decisions are considered being made under risk. The differences mentioned become visible in their deci-sion-making process, where small businesses act pursuant to a practical rea-soning whereas banks employ an analytical reasoning. Consequently, it leads to a clash when these two shall interact and function in a transaction as partners. The study concludes that the Financial Gap can be explained by small firms and banks speaking different languages when presenting the same reality.
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Liu, Ying. "Heteroepitaxial growth of InN and InGaN alloys on GaN(0001) by molecular beam epitaxy." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B36363558.
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Liu, Ying, and 劉穎. "Heteroepitaxial growth of InN and InGaN alloys on GaN(0001) by molecular beam epitaxy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B36363558.
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Reynolds, Jon. "Characterisation of the inositol 1,3,4,5- tetrakisphosphate-binding GTPase-activating protein, GAP1'I'P'4'B'P." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310690.
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Khattak, Shaukat Ali. "Exciton confinement in strain-engineered InAs quantum dots in metamorphic In_{x}Ga_{1-x}As." Thesis, Lancaster University, 2015. http://eprints.lancs.ac.uk/77217/.
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In this work, magneto-photoluminescence at low temperature, 4.2 K, is used to probe the exciton confinement in strain-engineered InAs/In_{x}Ga_{1-x}As/GaAs metamorphic quantum dots (QDs), emitting at telecom wavelengths (1.3 µm - 1.6 µm). The emission wavelength can be tuned by changing two independent parameters, i.e.,indium content, x, in In_{x}Ga_{1-x}As upper and lower confining layers and thickness of lower confining layer (LCL), d. Varying x changes the band offset and QD-CLmismatch (strain inside the QD), while varying d changes only QD-CL mismatch. We investigate the dependence of confinement on the QD-CL mismatch and band offset. Zero-magnetic-field spectra showed that wavelength (PL energy) increases(decreases) with increasing x, for a constant d, and with increasing d, for a constant x, which was attributed to be due to relaxation of strain inside the QD that is, in turn,a function of x and d. No correlation between wavelength and intensity was observed. Magneto-photoluminescence results revealed that for a subset of samples, the exciton effective mass increases linearly, more or less, with increasing QD-CL mismatch (QD strain), while its Bohr radius has no correlation with mismatch. The diamagneticshift coefficient increases 12-fold with decreasing mismatch from ∼ 7.5 % to 4.5 %, which is attributed to low effective mass, which in turn, is due to low QD strain. For high mismatch ( > 5.8 %), the Bohr radius is not determined, implying that it is less than10 nm, smaller than the dot radius. For indium composition x = 0.28 and 0.31, and for d > 1000˚A, the wave-function spills over out of the dot. For x = 0.35, the Bohr radii are, counter intuitively, found to be smaller than for samples with larger band offset (x = 0.31). Initially, it was explained as a spilling of the wave-function over vertically resulting in strong lateral confinement of exciton, but this explanation is not supported by our model calculations. Another explanation is, therefore, presented by carrying out temperature dependence and magnetic field dependence, at various temperatures, of PL energy: there are different dots, at x = 0.35, with different size where thermal escape of carriers from smaller dots to bigger ones occurs with increasing temperature, and the PL energy, in magnetic field, is contributed more by smaller dots than the bigger ones.
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Farkašová, Anna. "Revenue Recognition in Software Industry: Apple Inc. Case Study." Master's thesis, Vysoká škola ekonomická v Praze, 2017. http://www.nusl.cz/ntk/nusl-359072.
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Rapid digitization of enterprise processes and software applications simplifying daily-life routines enhance the need for software arrangements. Based on this growing trend, the underlying thesis discusses revenue recognition for software arrangements under US GAAP, the lingua franca of financial reporting framework in software industry. The thesis examines the first industry-specific guidance - SOP 97-2, its successor ASC 605 and aims at capturing the main implications resulting from the new converged US GAAP/ IFRS revenue recognition standard ASC 606/ IFRS 15 on a case study. The five-step revenue recognition model introduced by ASC 606 is applied to the US-based technology and software seller Apple Inc. and its wide range of product portfolio including software.
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Kim, Alexander Walter. "Construction and validation of a GC-ICP-MS instrument for the analysis of organometals and other trace element species." Thesis, University of Plymouth, 1993. http://hdl.handle.net/10026.1/1676.
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Swartz, Craig H. "Hall effect and photoconductivity lifetime studies of GaN, InN, and Hg₁-[subscript x]Cd[subscript x]Te." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4450.
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Thesis (Ph. D.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains ix, 72 p. : ill. Includes abstract. Includes bibliographical references (p. 68-72).
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Parala, Harish. "Precursor routes to selected metal and semiconductor nanomaterials crystals, composites, colloids of Au, GaN, InN, CdSe and TiO₂ /." [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=96870901X.
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Parala, Harish. "Precursor routes to selected metal and semiconductor nanomaterials crystals, composites, colloids of Au, GaN, InN, CdSe and TiO2 /." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=96870901X.
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Rosa, Celso Pereira Tome. "Efeitos da pressão uniaxial nos lasers de semicondutores de In1-xGaxAsyP1-y e de poço quântico de Ga1-xALxAs." [s.n.], 1985. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277178.
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Orientador: Theresinha de Jesus Serra de MattosDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Neste trabalho, estudamos o comportamento dos lasers semicondutores de InGaAsP-DH e GaAlAs-QW, quando submetidos a aplicação de pressão uniaxial. Na primeira parte, fazemos uma correlação entre os dados experimentais, obtidos para a variação da corrente limiar com aumento da pressão uniaxial dos lasers de InGaAsP, e a teoria desenvolvida por Patel e outros para os lasers de GaAs. Previa-se, teoricamente, um aumento da corrente limiar com a pressão, o que foi observado para 80% dos lasers testados; para os 20% restantes observamos uma redução da corrente limiar. Acreditamos que tal redução possa ser explicada supondo-se a presença do mecanismo de recombinação não radiativo (efeito Auger) nestes lasers. Acreditamos também, que anão homogeneidade observada nos resultados é devida a um desajustamento nos parâmetros de rede das camadas. Na segunda parte, fazemos um estudo sobre o guiamento da luz em laser de poço quântico de GaAlAs, analisando-se o guia de ondas nas direções transversal e paralela a camada ativa. Observamos experimentalmente um atraso na emissão estimulada. Este atraso é função da corrente de injeção e pode ser explicado supondo-se a existência de um guia de ondas induzido pelo efeito da temperatura. Uma comparação entre os resultados experimentais e teóricos para o laser de SCH-QW de GaAlAs de espessura da camada ativa de 200Þ apresenta boa concordância. Além do estudo da evolução do ganho com o tempo, observamos experimentalmente que a aplicação de pressão uniaxial causa um aumento no atraso da emissão estimulada. Este aumento no atraso é devido a uma redução do ganho modal. Uma relação empírica que mostra a evolução do ganho modal com a pressão uniaxial é proposta
Abstract: Not informed.
Mestrado
Física
Mestre em Física
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Widmann, Frédéric. "Epitaxie par jets moléculaires de GaN, AlN, InN et leurs alliages : physique de la croissance et réalisation de nanostructures." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10234.
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Ce travail a porte sur la croissance epitaxiale des nitrures d'elements iii gan, aln, et inn, en utilisant l'epitaxie par jets moleculaires assistee par plasma d'azote. Nous avons optimise les premiers stades de la croissance de gan ou aln sur substrat al#2o#3 (0001). Le processus utilise consiste a nitrurer la surface du substrat a l'aide du plasma d'azote, afin de la transformer en aln, puis a faire croitre une couche tampon d'aln ou de gan a basse temperature, avant de reprendre la croissance de gan ou aln a haute temperature (680 a 750c). Nous avons en particulier etudie les proprietes d'une couche de gan en fonction de la temperature a laquelle est realisee l'etape de nitruration. Lorsque les conditions de demarrage de la croissance sont optimisees, nous avons pu observer des oscillations de rheed pendant la croissance de la couche de gan. Nous avons etudie l'effet du rapport v/iii sur la morphologie de surface et les proprietes optiques et structurales de cette couche. Nous avons propose l'utilisation de l'indium en tant que surfactant pour ameliorer ces proprietes. Nous avons ensuite aborde la realisation de superreseaux gan/aln dont nous avons optimise les interfaces. Les mecanismes de relaxation des contraintes de aln sur gan et gan sur aln ont ete etudies. Nous avons egalement elabore les alliages algan et ingan, comme barrieres quantiques dans les heterostructures. Nous avons montre que la relaxation elastique des contraintes de gan en epitaxie sur aln donne lieu a la formation d'ilots de tailles nanometriques, qui se comportent comme des boites quantiques. Leur densite et leur taille dependent de la temperature de croissance, et des conditions de murissement apres croissance. Les proprietes optiques de ces ilots sont gouvernees a la fois par les effets de confinement quantique et par le fort champ piezo-electrique induit par la contrainte dans les ilots.
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Colussi, Marcio Luiz. "Investigação teórica sobre possíveis aplicações na eletrônica de nanofios de AlN, GaN e InN: um estudo de primeiros princípios." Universidade Federal de Santa Maria, 2012. http://repositorio.ufsm.br/handle/1/3910.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorUsing the formalism of Density Functional Theory with spin polarization and the Generalized Gradient Approximation for exchange and correlation term, we studied the stability and electronic properties of substitutional impurities of C, Si and Ge in GaN, AlN and InN nanowires and the variation of the band offset with the diameter variation in AlN/GaN nanowires heterojunctions. For the study of substitutional impurities we use AlN, GaN and InN nanowires in the wurtzite phase with diameter of 14.47 Å, 14.7 Å and 16.5 Å, respectively. For the study of variation of the band offset with the diameter of the nanostructure, we use nanowires in the wurtzite phase with a mean diameter ranging from 0.99 nm to 2.7 nm and the zinc blende phase with an average diameter ranging from 0.75 nm to 2.1 nm. The electronic structure calculations show that of GaN, AlN and InN nanowires are semiconductors with direct band gap at point Γ. To study the substitutional impurities, we consider that the impurity can occupy the cation or anion sites in non-equivalent positions that are distributed from the center to the surface of the nanowire. For the C impurities, in GaN nanowires, we find that when the C atom is substituted in the N site, it will be uniformly distributed along the diameter of the nanowire. When substituted at the Ga site, it will be preferably find on the surface of the nanowire. In this case, the formation energy of CGa is almost identical to the CN, thus can occur formation of the auto-compensed CN-CGa pair. In AlN nanowires, when the C atom occupying the N site, it is also observed an almost uniform distribution along the diameter of the nanowire with a small preference (less energy formation) to the surface sites. Since the formation energy of the CN is lower than CAl in all regions of the nanowires, taking thus more likely to form CN. For InN nanowires, in the center sites, the formation energy of the CN and CIn is very similar, and the CN will have a uniform distribution along the diameter, but on the surface of the CIn is more stable and band structure show that this configuration has shallow donor levels. For Ge substitutional impurities in GaN nanowires, we observed that the center of the nanowire, the Ge atom is more likely to be found located in the Ga site, but in surface to find the most likely of N site, this being the most stable configuration. For AlN nanowires, the center of nanowire is possible to find the Ge atom at the N or Al sites, as the formation energy is practically the same. On the surface the more likely it is to find the Ge atom of the N site, which also is the most stable configuration. As for InN nanowires, the Ge atom will be found preferably at the In site with uniform distribution along the diameter of the nanowire. Analyzing the band structure of GeIn observed shallow donor levels. For the Si substitutional impurities, we obtain that in GaN and InN nanowires of the most stable configuration, the Si atom is to be found at the cation (Ga and In) sites in the central sites of the nanowire and analyzing the band structure of SiGa and SiIn, we also observed shalow donor levels. However, for AlN nanowires in the centerof the nanowire is greater the probability of finding the Si atom at the Al site, but the surface is greater the probability of finding the Si atom at the N site which is the most stable configuration. Finally, we analyze the variation of the band offset to the change in diameter of the nanowires forming the heterostructure. We consider heterostructure on yhe wurtzite and zinc blende phases, therefore during the synthesis the two phases are obtained. We found that the result is similar for the two phases and the extent that the diameter increases the value of the band offset also increases, tending to the value obtained for the bulk.
Usando o formalismo da Teoria do Funcional da Densidade com polarização de spin e a aproximação do gradiente generalizado para o termo de troca e correlação, estudamos a estabilidade e as propriedades eletrônicas de impurezas substitucionais de C, Si e Ge em nanofios de GaN, AlN e InN e a variação do band offset com o diâmetro em heteroestruturas da nanofios AlN/GaN. Para o estudo de impurezas substitucionais utilizamos nanofios de AlN, GaN e InN na fase da wurtzita e com diâmetros de 14,47 Å, 14,7 Å e 16,5 Å, respectivamente. Já para o estudo da variação do band offset com o diâmetro da nanoestrutura, utilizamos nanofios que formam a heteroestrutura na fase wurtzita com diâmetro médio variando 0,99 nm até 2,7 nm e na fase blenda de zinco com diâmetro médio variando de 0,75 nm até 2,1 nm. Os cálculos de estrutura eletrônica apresentam que os nanofios de AlN, GaN e InN são semicondutores com gap direto no ponto Γ. Para o estudo das impurezas substitucionais, consideramos que a impureza pode ocupar o sítio do cátion ou do aniôn, em posições não equivalentes que estão distribuídas do centro até a superfície do nanofio. Para a impureza de C, em nanofios de GaN, obtemos que, quando o átomo de C for substituído no sítio do N, o mesmo vai estar distribuído uniformemente ao longo do diâmetro do nanofio. Já quando substituído no sítio do gálio, o mesmo vai ser encontrado preferencialmente na superfície do nanofio, sendo que, na superfície do nanofio a energia do formação do CGa é praticamente a mesma do CN, assim pode ocorre a formação de pares autocompensados CN-CGa. Em nanofios de AlN, quando o átomo de C ocupar o sítio do N, também vai ter uma distribuição quase uniforme ao longo do diâmetro do nanofio com uma pequena preferência (menor energia de formação) para os sítios da superfície. Sendo que a energia de formação do CN é menor que do CAl em todas as regiões do nanofios, tendo assim, probabilidade maior de formar CN. Para nanofios de InN, nos sítios do centro, a energia de formação do CN e CIn é muito próxima, sendo que o CN vai ter distribuição uniforme ao longo do diâmetro, mas na superfície o CIn ser torna mais estável e a estrutura de bandas mostra que esta configuração apresenta níveis doadores rasos. Para impurezas substitucionais de Ge, em nanofios de GaN, observamos que no centro do nanofio, o átomo de Ge tem uma probabilidade maior de ser encontrado no síto do Ga, mas nos sítios da superfície a probabilidade é maior de encontrar no sítio do N, sendo essa a configuração mais estável. Para nanofios de AlN, no centro do nanofio, é possível encontrar o átomo de Ge no sítio do N ou Al, já que a energia de formação é práticamente a mesma. Na superfície a probabilidade maior é de encontrar o átomo de Ge no sítio do N, sendo, também, esta a configuração mais estável. Já para nanofios de InN, o átomo de Ge vai ser encontrado preferencialmente no sítio do In com distribuição uniforme ao longo do diâmetro do nanofio. Analisando a estrutura de bandas do GeIn observamos níveis doadores rasos. Para a impureza substitucional de Si, obtemos que em nanofios de GaN e InN a configuração mais estável, é o Si ser encontrado no sítio do cátion (Ga ou In) nos sítios centrais do nanofio e analizando a estrutura de bandas do SiGa e do SiIn, também observamos níveis doadores rasos. Entratanto, para nanofios de AlN, no centro do nanofio a probabilidade é maior de encontrar o átomo de Si no sítio do Al, mas na superfície a probabilidade é maior de encontrar o átomo de Si no sítio do N, sendo esta a configuração mais estável. Por fim, analisamos a variação do band offset com a variação do diâmetro do nanofios que forma a heteroestrutura. Consideramos heteroestruturas na fase wurtzita e blenda de zinco, pois nos processos de síntese as duas fases são obtidas. Observamos que o resultado é similar para as dias fases e, a medida, que o diâmetro aumenta o valor do band offset também aumenta, tendendo para o valor obtido para o cristal.
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Srdar, Nujoud Abdullah. "The gap between learning and teaching in accounting education : the Saudi Arabian experience." Thesis, University of Portsmouth, 2017. https://researchportal.port.ac.uk/portal/en/theses/the-gap-between-learning-and-teaching-in-accounting-education(87d43aba-3a40-4a7d-aada-9ea77783080a).html.
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Over the past few decades, there has been an expectation gap between what accounting education has delivered and what accounting practice has received. Practitioners want university education to train students for specific tasks and circumstances to prepare them for the reality of the work environment. On the other hand, academics want university education to be broad and comprehensive, and carrying an academic character. The research has made significant contributions to knowledge regarding the nature of the gap between accounting learning and practice in SA. The study has revealed unexpected results in relation to the gap in accounting education, which can be explained through the profession's first appearance in SA and the influence of the American accounting framework on professional accounting education in SA. Moreover, this study has made other contributions in terms of methodology, theory, and practice. This study uses a novel framework to understand the gap, in the context of Saudi Arabia. The study uses an abductive approach to investigate the 'what' and ' why' reasons for the gap, characterize its details, and propose recommendations for bridging it. It is the first of its kind to analyse qualitatively the perspectives of five main groups of stakeholders in the accounting system (accounting educators, final year students, fresh employees (1-4 year of experience), the professional body and employers) and compare their perspectives about the competencies of accounting graduates. The findings show that a gap between learning and practice exists in university accounting education in Saudi Arabia. Employers believe that accounting graduates lack the required technical competencies for the workplace. All participant groups affirmed that collaboration between the profession and the academic is in order, to bridge this gap. University accounting curricula need to change and be updated in order to meet the rapid developments in the business environment.
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Santos, Flavia Ferreira de Souza dos 1985. "Implantação do plano de gestão de resíduos químicos da FT-UNICAMP = oxidação de herbicidas triazínicos com 'H IND. 2 O IND. 2' e metaloporfirinas." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267795.
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Orientador: Maria Aparecida Carvalho de MedeirosDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Tecnologia
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Resumo: Os resíduos químicos gerados em laboratórios de universidades são complexos devido a grande diversidade dos processos de geração e dos compostos que os constituem. Dessa forma, há necessidade de um plano de gestão para evitar que esses resíduos de composição diversificada sejam dispostos inadequadamente no meio ambiente. Nesse contexto encontra-se em implantação o Plano de Gestão de Resíduos Químicos (PGRQ) dos Laboratórios de Ensino e Pesquisa da Faculdade de Tecnologia - FT/UNICAMP. Com a finalidade de contribuir para a implantação do PGRQ da FT, o presente projeto visou realizar ações de gestão, tais como o diagnóstico qualitativo e quantitativo dos resíduos gerados em todos os laboratórios da FT, buscar ações de minimização de geração, a divulgação do programa de gestão à comunidade acadêmica usuária dos laboratórios e a avaliação de possíveis alternativas de tratamento de resíduos. O levantamento periódico dos resíduos permitiu traçar o perfil de geração dos laboratórios da FT, fundamental para a implantação do plano de gerenciamento. A primeira transferência de resíduos ao abrigo externo e o oferecimento do curso de capacitação resultaram na redução da quantidade de resíduos gerados. No laboratório de cromatografia da FT tem sido realizado há alguns anos o monitoramento de herbicidas triazínicos em amostras ambientais, o que levou a geração desses resíduos orgânicos perigosos. Perante essa condição, foi avaliada uma alternativa de tratamento avançado, via reação de oxidação catalisada por metaloporfirinas, para a degradação dos resíduos de herbicidas triazínicos. As reações de oxidação dos herbicidas triazínicos e os subprodutos gerados foram monitorados por espectrofotometria UV-Vis e cromatografia gasosa. Os rendimentos das reações de oxidação das triazinas com H2O2 e catalisadas pelas metaloporfirinas de ferro (Fe(FTTPCl)) e rutênio (Ru(OCTTPP), variaram de acordo com as condições de reações para a simazina de 9% a 74% e para a atrazina de 12% a 67%, utilizando a Ru(OCTTPP), sendo que para a Fe(FTTPCl) foram de 1,7% a 66% para a simazina, enquanto que para a atrazina foram de aproximadamente 20% nas melhores condições
Abstract: The chemical waste generated in laboratories of universities are complex due to the great diversity of processes of generation and compounds that comprise them. Thus, there is need for a management plan to prevent the waste of diverse composition are inadequately disposed in the environment. In this context are in implementing the Chemical Waste Management Program of Teaching and Research Laboratories of the Faculty of Technology - FT / UNICAMP. With purpose of contribute to the implementation of the FT's Management Program, this project aimed to carry out management actions as the qualitative and quantitative diagnostic of the waste generated in the whole laboratories from FT, to look for actions to minimize the waste generation, dissemination of management program for the academic community users of the laboratory and the evaluation of possible alternatives for waste treatment. The periodic survey of waste allowed tracing the profile generation FT Laboratories, has been crucial for the implementation of the management plan. The first waste transference for the external shelter and the offering of the training course resulted in reducing the amount of waste generated. In the chromatography laboratory of FT was performed for several years monitoring triazine herbicides in environmental samples, with the generation of hazardous organic wastes. In this connection, the another aim of the present work has focused in a advanced treatment alternative by oxidation reaction catalyzed by metalloporphyrins for the degradation of triazine herbicides residues. The oxidation reactions of the triazines herbicides wtih H2O2 and catalized by iron (Fe(FTTPCl) and ruthenium (Ru(OCTTPP)) metalloporphyrins were obtained with variation according to the reactions conditions, from 9% to 74% for simazine and from 12% to 67% for atrazine, using Ru(OCTTPP), while for Fe(FTTPCl) the yields were from 1.7% to 66% for simazine and ca. 20% for atrazine at the best conditions
Mestrado
Tecnologia e Inovação
Mestre em Tecnologia
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Sall, Mamour. "Irradiation par des ions de grande énergie de semiconducteurs III-N (AlN, GaN, InN) : création de défauts ponctuels et étendus." Phd thesis, Université de Caen, 2013. http://tel.archives-ouvertes.fr/tel-00936879.
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Les matériaux semiconducteurs III N (AlN, GaN, InN) présentent des propriétés intéressantes pour la micro et l'opto-électronique. Ils peuvent être soumis à différents types d'irradiation dans une large gamme d'énergie de projectile. Dans l'AlN, initialement considéré insensible aux excitations électroniques (Se), nous avons mis en évidence une synergie inédite entre Se et les chocs nucléaires (Sn) pour la création de défauts absorbants à 4.7 eV. Par ailleurs, un autre effet du Se est mis en évidence dans l'AlN : les dislocations vis subissent, sous l'effet du Se, une montée aux fortes fluences d'irradiation. Dans le GaN, deux mécanismes de création peuvent être à l'origine des défauts absorbants à 2.8 eV: une synergie entre Se et Sn, ou une création uniquement due à Sn mais avec un fort effet de la taille des cascades de déplacement. L'étude, par MET, des effets de Se dans les trois matériaux, montre un comportement très différent d'un matériau à l'autre bien qu'ils appartiennent à la même famille des nitrures avec la même structure atomique. Sous irradiation aux ions monoatomiques (vitesse entre 0.4 et 5 MeV/u), tandis que l'on observe des traces discontinues dans le GaN et l'InN, aucune trace n'est observée dans l'AlN avec le plus fort pouvoir d'arrêt électronique (33 keV/nm). Il faut des fullerènes pour observer des traces dans l'AlN. Le modèle de la pointe thermique inélastique a permis de calculer les énergies nécessaires pour produire des traces dans l'AlN, le GaN et l'InN, elles sont respectivement de 4.2 eV/atome, 1.5 eV/atome et 0.8 eV/atome. Cette différence de sensibilité aux effets de Se, se retrouve également aux fortes fluences d'irradiation.
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Hawkey, Suzanna. "Bridging the gap between detection and confirmation of B. anthracis in blood cultures." Thesis, University of Portsmouth, 2015. https://researchportal.port.ac.uk/portal/en/theses/bridging-the-gap-between-detection-and-confirmation-of-b-anthracis-in-blood-cultures(74b1684e-10e3-4b75-8ccc-8f2c9eefc27d).html.
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The spore forming bacterium, Bacillus anthracis is the aetiological agent of anthrax. The 2001 US anthrax letter attacks and the 2009‐2010 outbreak of injectional anthrax in the UK highlighted the importance of early detection and confirmation of this agent, both for patient outcome and forensic investigations. A reliable and consistent method was used in this study to safely simulate blood cultures with B. anthracis and used to determine the time to positive detection. This was performed with different strains and with varying concentrations of inoculum. An inverse linear relationship was observed with all strains and used to estimate the bacterial blood concentration of anthraxpatients based on data gathered from the literature and front‐line laboratories in the UK. The study explored a method to potentially reduce the turnaround times for the confirmation of B. anthracis at the national reference laboratory. Serum separator tubes were used to concentrate the bacteria from simulated blood cultures. A simple wash step was performed prior to performing confirmatory phenotypic tests and inactivation for rapid molecular detection. A comparison of test results with and without serum separator tube processing was made for B. anthracis and bacterial isolates referred during the outbreak of injectional anthrax. Simulated mixed blood cultures of B. anthracis and possible common contaminants were also tested. Compared to routine methods, confirmatory phenotypic test results were achieved 24 hours sooner using the method. The simple wash step and inactivation was sufficient to provide nucleic acid for molecular confirmatory assays and genotyping. A new ‘sample to answer’ platform, the Biofire Filmarray® was also trialled and correctly identified B. anthracis directly from simulated blood culture and provided results within one hour. Aspects relating to potential biosafety concerns for processing B. anthracis blood cultures were explored. The data generated suggests the aerosol risk is low for B. anthracis. Viability of material on microscopy slides was examined and the data supports the recommended use of alcohol fixation for slide preparation. There has been no previous evidence reported for sporulation occurring in blood culture bottles and the study findings suggest this is possible five days post positive detection. Interactive e‐learning modules have been produced to disseminate the study outcome. The e‐learning is intended for front‐line laboratories to raise awareness for the safe handling and laboratory identification of B. anthracis.
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Wang, Yiren. "Modelling and characterisation of losses in nanocrystalline cores." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/modelling-and-characterisation-of-losses-in-nanocrystalline-cores(eddd2c60-7322-4665-9176-b45e53621285).html.
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Increasing the power density of the DC-DC converters requires the size and weight of the magnetic components, such as inductors and transformers, to be reduced. In this thesis, the losses in nanocrystalline inductor cores are characterised and analysed, including the traditional core loss and the gap loss caused by the air gap fringing flux. The loss calculations will form a basis for the design and optimisation of high power inductors for DC-DC converters for EV applications. This thesis first characterises experimentally the core losses in four nanocrystalline cores over a range of operating conditions that are representative of those encontered in typical high power converter applications, including non-sinusoidal waveforms and DC bias conditions. The core losses are assessed by the measured B-H loops and are characterised as a function of DC flux density, showing that for a fixed AC induction level, the losses can vary by almost an order of magnitude as the DC bias increases and the duty ratio moves away from 0.5. The results provide a more complete picture of the core loss variations with both DC and AC magnetisations than is available in manufactures’ data sheets. An electromagnetic finite element (FE) model is used to examine the gap loss that occurs in finely laminated nanocrystalline cores under high frequency operation. The loss is significant in the design example, contributing to almost half of the total inductor loss, and the gap loss is highly concentrated in the region of the air gap. The dependence of the gap loss on key inductor design parameters and operating condtions is also explored. An empirical equation is derived to provide a design-oriented basis for estimating gap losses. Thermal finite element analysis is used to estimate the temperature rise and identify the hot spot in a nanocrystalline inductor encapsulated in an alumimium case. The temperature distribution in the core largely corresponds to the non-uniform distribution of the gap loss. The thermal FEA can also be used to evaluate different thermal management methods to optimise the design for a more compact component. The FE modelling of gap loss and the thermal predictions are validated experimentally on a foil-wound Finemet inductor, showing good agreement between the predictions and measurements under various operating conditions.
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Gotschke, Tobias. "Untersuchungen zum geordneten Wachstum von III-Nitrid Nanodrähten." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16466.
Full textAbstract:
Diese Arbeit behandelt den Einfluss der Mg- und Si-Dotierung auf das Wachstum von InN-Nanodrähten (ND) sowie die Etablierung, Anwendung und Analyse des selektiven Wachstums von GaN-ND auf Si-Substraten. Das Ziel der Arbeit ist dabei die Herstellung von ND mit homogenen Abständen, Durchmessern und Längen. Zunächst wird die Si- und Mg-Dotierung von InN-ND untersucht. Dazu werden die einzelnen Wachstumsparameter variiert und deren Einfluss analysiert. Für die Si-Dotierung kann dabei eine nicht lineare Abhängigkeit der Morphologie der Nanodrähte mit der Substrattemperatur, dem In- und Si-Fluss beobachtet werden, sowie eine Erweiterung der Wachstumstemperatur zu Werten oberhalb des Einsetzens der Dekomposition bei gleichzeitig verbesserter Homogenität der Länge und des Durchmessers der ND. Für die Mg-Dotierung von InN-ND wird kein Einfluss auf die Morphologie beobachtet. Durch optische und elektrische Messungen wird ein Hinweis auf das erfolgreiche Einbringen der Mg-Atome als Akzeptoren beobachtet. Nach einer Voruntersuchung anhand von nicht-selektivem Wachstum bei hohen Substrattemperaturen, sowie einer Untersuchung zur Dekomposition von GaN-ND werden die Wachstumsparameter für das selektive Wachstum mit einem neuentwickelten Ansatz eingegrenzt. Anschließend wird innerhalb dieser Grenzen der Einfluss der Wachstumsparameter auf das selektive Wachstum untersucht. Ein Schwerpunkt dieser Untersuchungen wird auf die Nukleation gesetzt, bei der anhand von Variationen des Substratdesigns (Maskentyp, -material sowie Substratmaterial) und direkten Analysen für kurze Wachstumszeiten ein neuartiges Nukleationsmodell vorgeschlagen wird. Ein zweiter Schwerpunkt wird auf die Diffusion der Ga-Atome gesetzt. Es wird ein geometrisches Modell zur Analyse der Diffusion auf dem Substrat und den Seitenfacetten vorgeschlagen und durch experimentelle Daten untermauert. Anhand des Modells ergeben sich Diffusionslängen von 400 nm auf dem Substrat respektive 500 nm auf den ND-Seitenfacetten.The influence of the Si- and Mg-doping of InN NWs as well as the selective area growth (SAG) of GaN NWs on Si substrates is developed, optimized and analyzed to obtain NWs with homogeneous periods, lengths and diameters. The variation of growth parameters for Si-doped InN NWs reveals a nonmonotonic morphology dependence and an extended growth window towards higher substrate temperatures. In addition, the NW density is reduced and the size homogeneity improved for high Si doping levels. In contrast, no impact on the morphology of the InN NWs is observed under Mg-doping. Nevertheless, indications of a successful incorporation of the Mg-acceptors are found by optical and electrical studies. The non-selective growth of GaN NWs at high substrate temperatures is investigated for various Ga-fluxes and substrate temperatures. Furthermore, the decomposition of GaN NWs is observed with an investigation of the NW morphology and the Ga desorption during growth. The nucleation on the mask (Si) and the substrate (AlN) is investigated with a new approach to define a growth window for the SAG. Within this window, the influence of the substrate temperature, growth time, Ga- and N-flux on the SAG is investigated by a separate variation for each parameter. An optimal set of growth parameters with respect to a homogeneous NW morphology is obtained. The growth on substrates with different mask types, mask materials and substrate materials reveals a novel nucleation mechanism. The asymmetric nucleation in the holes of the mask could be attributed to a local increase in the Ga-supply by blocking the impinging Ga-flux at the vertical sidewalls. The diffusion of Ga-atoms on the substrate and the NW is finally investigated. A descriptive model is proposed and the fit to experimental data reveals a diffusion length of 400 nm. The limitation of the axial growth is explained by the diffusion length of Ga atoms on the NW sidewall and a diffusion length of approximately 500 nm is obtained.