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Ma, Pui-wai, et 馬培煒. « Transport properties of InAs/(A1Sb)/GaSb/(A1Sb)/InAs heterostructure systems ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B30474188.
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Butera, Silvia. « InAs avalanche photodiodes ». Thesis, Heriot-Watt University, 2015. http://hdl.handle.net/10399/3043.
Texte intégralRésumé :
The ability to efficiently detect low-level light in the infrared above wavelengths of 1.7 μm is becoming increasingly important for many applications such as gas sensing, defence/geoscience ranging and clinical thermography. The III-V narrow gap semiconductor InAs, with a bandgap of 0.36 eV, is well known for its use as a conventional photodiode. The aim of this thesis was to design, build and test InAs devices for use as reverse biased avalanche photodiodes. In order to fabricate a lownoise detector, a passivation study was conducted. For the first time we report the achievement of high quality single crystal II-VI passivation layers on InAs mesa structures. Pre-growth surface oxide removal processes were developed to improve surface morphology of II-VI layers grown on InAs samples. ZnSe and ZnTe successfully terminate the InAs mesa devices preventing atmospheric oxidation. Low surface leakage currents are observed at low reverse bias and at room temperature for both materials. LIDAR at wavelengths greater than 2 μm was studied using these InAs mesa photodiodes, showing potential to take advantage of the low solar background at these wavelengths. For the first time, laboratory based LIDAR experiments, with ranges of around 0.5 metre stand-off distance, were performed with InAs n-i-p edge illuminated mesa photodiodes, used in linear multiplication mode. Time-of-flight measurements were demonstrated at wavelengths from 1.3 μm to 2.365 μm. A 6 mm ranging error was observed in these short range measurements.
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LOPES, ARTUR JORGE DA SILVA. « GROWTH OF QUANTUM DOT TO THE FAMILIES INAS/INP, INAS/INGAAS E INAS/INGAALAS FOR FOTODETECTORS OF INFRARED RADIATION ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=12288@1.
Texte intégralRésumé :
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOPontos quânticos (PQs) auto-organizáveis de InAs sobre InP, InGaAs, InGaAlAs utilizando-se substratos de InP foram crescidos pela deposição química de metal-orgânicos (MOCVD) e foram investigadas para fotodetectores. Para PQs de InAs crescidos sobre diferentes substratos de InP, têm-se que a presença de discordâncias é responsável pelo aumento na densidade planar dos PQs. O espectro de fotoluminescência (FL) das estruturas de InP/InxGa1-xAs/InAs/InP, com diferentes composições da camada ternária. Medidas com microscopia de força atômica (AFM) mostraram que os PQs mais altos são obtidos quando os mesmos são crescidos sobre uma camada de InxGa1-xAs com um descasamento de 1000ppm, e a altura decresce com o descasamento a partir deste valor. O espectro de FL dos PQs mostrou uma banda assimétrica, a qual envolve transições entre os níveis de energia dos PQs e pode ser decomposta em dois picos. Pico de energia mais alta desta banda foi observado para a amostra com PQs crescidos sobre uma camada de InxGa1-xAs casada e o pico foi deslocado para energias mais baixas para amostras tensionadas. Estruturas diferentes de PQ de InAs crescidas sobre uma camada de InGaAlAs casada com InP foram investigadas. Picos de fotocorrente extremamente estreitos foram observados, demonstrando um excelente potencial para sintonização estreita de comprimentos de onda. Foram desenvolvidas estruturas para detectar radiação superior à 10μm. Medidas de absorção mostrando uma dependência com a polarização mostraram eu as estruturas tem um confinamento total e são apropriadas para detecção sintonizável de radiação por incidência normal.
Self-assembled InAs quantum dots (QD) over an InP, InGaAs, InGaAlAs on InP substrates were grown by metal-organic chemical vapor deposition (MOCVD) and were investigated for quantum dot infrared photodetectors. For InAs QD over an InP buffer on different InP substrates. The results indicate that the presence of dislocations were responsible for the increase in the QD density. Photoluminescence (PL) spectra of InP/InxGa1-xAs/InAs/InP dot-in-a-well structures, with different compositions of the ternary layer. Measurements with atomic force microscopy showed that the largest QD height is obtained when the InAs QDs are grown on the InxGa1-xAs layer with a mismatch of 1000ppm, and the height decreases as the mismatch departs from this value. PL spectra of the QDs showed an asymmetric band, which involves transitions between dot energy levels and can be deconvoluted into two peaks. The highest energy PL peak of this band was observed for the sample with the QDs grown on top of the lattice-matched InxGa1-xAs and it shifted to lower energies for strained samples as the degree of mismatch increased. Different InAs quantum dot structures grown on InGaAlAs lattice matched to InP. Extremely narrow photocurrent peaks were observed, demonstrating great potential for fine wavelenght selection. Structures which can detect radiation beyond 10ìm were developed. Polarization dependence measurements showed that the structures have a zero- dimensional character and are suitable for detection of normal incidence light.
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IOVENITTI, SIMONE. « ASTROMETRY TECHNIQUES FOR THE CALIBRATION OF THE ASTRI TELESCOPE WITH THE VARIANCE METHOD ». Doctoral thesis, Università degli Studi di Milano, 2022. http://hdl.handle.net/2434/914143.
Texte intégralRésumé :
In the study of Very High-Energy (VHE) astrophysical phenomena the next generation of Imaging Atmospheric Cherenkov Telescopes (IACT) will play a key role thanks to specific ground-based astronomical observations. In this context, the ASTRI project developed a novel instrument endowed with a Schwarzschild-Couder dual-mirror optical configuration (that has never been adopted before in gamma-ray astronomy) and a dedicated Cherenkov camera entirely designed by the Istituto Nazionale di Astrofisica (INAF) based on SiPM sensors. The prototype telescope ASTRI– Horn is located in Italy and carried out successfully in 2019 the techno- logy validation phase, paving the way for the realization of the MiniAr- ray: 9 identical telescopes working in stereoscopic mode to be installed in Tenerife (Canary Islands) within the next three years. However, several issues related to the pointing performances emerged during operations with ASTRI–Horn. Actually, the pointing calibration is generally a critical aspect for Cherenkov telescopes, as their cameras are designed for the detection of nanosecond atmospheric flashes rather than for imaging the starfield and, consequently, it is impossible to use the standard astrometry of the focal plane. Furthermore, in the case of ASTRI, the compactness of the mechanical structure prevents from installing an auxiliary monitoring camera sharing the same optical system of the telescope. Despite these difficulties, the optimization of the pointing performances is crucial for ensuring the scientific accuracy of the whole system.
The present PhD thesis aims at the development and validation of new astrometric techniques for the pointing calibration of the ASTRI telescope exploiting the so-called Variance method, a statistical algorithm implemented in the Cherenkov camera electronic board. Thanks to the Variance, the AS- TRI telescope is endowed with an ancillary output owning the potentiality to image the stellar component of the night sky background in the Field of View (FoV), with a quite coarse angular resolution (~11°, corresponding to the pixel size of the Cherenkov camera), but a relatively good sensitivity for an IACT (visual magnitude limit ~7). As we discuss in this document the Variance constitutes a unique opportunity for enhancing the pointing performances of the telescope, and we demonstrate that our procedures offer a chance to reach the critical accuracy level required for achieving the scientific objectives of the ASTRI project.
Unfortunately, in this period the COVID-19 pandemic and other accidental events, heavily delayed the maintenance operations on the ASTRI– Horn telescope, and up to now it is still impossible to make new observations dedicated to the validation of our procedures, hence only data taken in previous months were used. As in any other experimental activity, new data taken on purpose would have considerably facilitated our work, but due to the present situation, we focused our attention on Variance data available in the ASTRI archive that has never been explored before. The resulting work represents the first complete and detailed analysis of the Variance method together with its numerous unexplored applications. Our custom astrometry techniques allowed us to reveal that ASTRI–Horn was affected by two kinds of systematic errors, that we characterized and measured for the first time. The experience gained with archive data allowed us to understand how to apply our routines for calibrating the incoming ASTRI MiniArray, indicating an effective strategy to match the crucial requirement for the pointing accuracy. The resulting procedure has already been inserted into the calibration plan of the MiniArray and its Online Observation Quality System (OOQS).
The structure of the present document is articulated in eight chapters and three appendices, whose content can be summarized as follows.
Chapter 1 presents the status of the art in VHE astrophysics, focusing on the observational features of cosmic rays and gamma rays, together with a description of the main open questions in this research field.
Chapter 2 is dedicated to IACTs, presenting their history and operating principles, and introducing the major examples of instruments currently in activity worldwide.
Chapter 3 focuses on the ASTRI project, presenting both the prototype telescope ASTRI–Horn and the incoming observatory of the MiniArray. In particular, it is reported a detailed description of the most relevant sub-systems for this thesis: the camera, the optical scheme, and the pointing strategy.
Chapter 4 goes into the details of the Variance method. A technical description of its functioning at the electronic level is provided at first, while the core of the chapter is dedicated to our routines for the production of sky images and their calibration.
Chapter 5 reports specific tools and procedures that we developed for the analysis of Variance images: the astrometric calibration, the de-convolution of the star signal, and the transformation function to correct the artifacts introduced by the geometric arrangement of the pixels.
Chapter 6 describes the algorithm to assess the alignment of the Cherenkov camera to the optical axis of the telescope exploiting the apparent rotation of the FoV during long observing runs in tracking mode.
Chapter 7 shows a custom procedure for the star identification developed on purpose for Variance images (as it is impossible to adopt the standard astrometry software for their analysis) allowing to monitor in real-time the actual pointing direction of the telescope.
Chapter 8 contains the concluding remarks. It summarizes the main results achieved in this thesis, highlighting their importance but also some limitations and suggesting further improvements. Future perspectives of this work are briefly presented at last, with particular attention to its implementation on the incoming ASTRI MiniArray.
At the end of this document, three appendices report additional/complementary material concerning respectively metrological techniques for the inspection of shape and reflectivity of primary mirror segments (A), more details about the software developed for this thesis and the access to it (B), and the massive activity of outreach and education carried out during the doctoral period in the field of Cherenkov astronomy (C).
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Pfund, Andreas. « Spin states in InAs nanowires / ». Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17861.
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Hill, Richard John Allan. « Tunnelling into InAs quantum dots ». Thesis, University of Nottingham, 2003. http://eprints.nottingham.ac.uk/10002/.
Texte intégralRésumé :
This thesis describes an experimental study of the electronic properties of semiconductor heterostructure tunnel devices. InAs self-assembled quantum dots (QDs) are incorporated into the barrier layer of a GaAs/AlAs/GaAs tunnel diode. When a voltage, V, is applied across the device, we observe resonant features in the tunnel current, I, whenever an electron state in one of the qds comes into resonance with an occupied electron state in the emitter. We employ an electron state of a single qd as a spectroscopic probe of a two-dimensional electron system (2DES), from the Fermi energy to the subband edge [1]. For magnetic field B applied parallel to the current, we observe peaks in the I(V) characteristics corresponding to the formation of Landau levels in the 2DES. We obtain quantitative information about the energy dependence of the quasiparticle lifetime, Tqp, of the 2DES. We find that Tqp ~ 2.5 hbar=(Ef - E), in contrast with the expectation for a normal Fermi liquid, but in agreement with predictions for a Fermi liquid state of a disordered 2DES. Close to filling factor nu = 1 we observe directly the exchange enhancement of the g factor. This thesis also describes the design, realisation and measurement of a tunnel diode incorporating InAs QDs and a series of 4 planar electrostatic gates. By applying a bias to the gates, it is possible to selectively inject current into a particular QD. We use magneto-tunnelling spectroscopy to determine the energy levels of the ground and excited state of a single QD, and to map the spatial form of the wave functions of these states [2]. The effect of pressure on the resonant tunnelling of the QDs is also described. [1] P. C. Main et al., Phys. Rev. Lett. 84, 729 (2000) [2] R. J. A. Hill et al., Appl. Phys. Lett. 79, 3275 (2001)
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Nelson, Mark D. « Integrated network application management (INAM) ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FNelson.pdf.
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Thesis (M.S. in Information Technology Management)--Naval Postgraduate School, December 2004.Thesis advisor(s): Alex Bordetsky. Includes bibliographical references (p. 85-86). Also available online.
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CHATTOU, BIDDINE SOAD. « Etude des effets du diabete sur le courant d'echange ina-ca, le courant calcique ical et la composante de courant sodique inal, dans les cardiomyocytes de rat ». Paris 7, 2000. http://www.theses.fr/2000PA077040.
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L'observation d'alterations de la fonction myocardique associees au diabete nous a conduits a analyser les effets de cette pathologie, induite experimentalement, sur des transporteurs d'ions calcium (ca 2 +) et sodium (na +), deux ions majeurs qui influencent a la fois le decours de l'activite electrique cellulaire cardiaque, et, directement (pour ca 2 +) ou indirectement (pour na +), la fonction contractile des myocytes. Dans la premiere partie de ce travail, nous avons enregistre, dans des cardiomyocytes de rats, le courant genere par l'echangeur na +/ca 2 + (i n a - c a) et le courant calcique i c a l. Nous avons pour ce faire utilise une methode d'enregistrement qui ne modifie pas le pouvoir tampon calcique intracellulaire, a savoir la technique de patchclamp en configuration patch perfore, par la nystatine. Le principal resultat de cette partie de notre etude est que la densite du courant d'echange i n a - c a (active par i c a l ou par l'application de cafeine) et la densite du courant calcique i c a l, sont diminuees dans les cardiomyocytes de rats diabetiques. La diminution de i c a l pourrait contribuer a diminuer le calcium -induced calcium release et par consequent l'activation de l'echangeur na + -ca 2 +. La diminution de i n a - c a pourrait resulter d'une moindre charge calcique du reticulum sarcoplasmique, comme semble l'indiquer le ralentissement de l'inactivation de i c a l. Nos resultats contribuent ainsi a expliquer la diminution d'amplitude de la variation transitoire calcique precedemment decrite chez les diabetiques et ses consequences sur l'activite contractile du myocarde. Dans la seconde partie de notre travail, nous avons analyse une composante de courant sodique a inactivation lente, i n a l, susceptible
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Disseix, Pierre. « Etude des proprietes electroniques de puits quantiques contraints inas/inp et inas/gaas par spectroscopie optique ». Clermont-Ferrand 2, 1994. http://www.theses.fr/1994CLF21652.
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Ce travail concerne l'etude experimentale et theorique des proprietes electroniques de puits quantiques fortement contraints inas/inp et inas/gaas. Les particularites de ces deux systemes sont, d'une part, le fort desaccord de maille (-3,2% pour inas/inp et -7,2% pour inas/gaas), et d'autre part, les faibles valeurs de l'energie de bande interdite et du couplage spin-orbite d'inas conduisant a des masses effectives peu elevees et a un couplage inter-bandes important. Des experiences de photoluminescence, d'absorption optique detectee thermiquement (aodt) et de reflectivite ont ete effectuees sur des puits quantiques simples inas/inp d'une a trois monocouches d'epaisseur, elabores par epitaxie en phase vapeur par la methode aux hydrures, et sur des multi-puits quantiques inas/gaas d'environ une monocouche d'epaisseur, realises par epitaxie sous jets moleculaires. Differentes transitions liees aux puits d'inas ont ete observees et la spectroscopie d'aodt a permis de mettre en evidence, pour la premiere fois dans le systeme inas/inp, la transition excitonique impliquant les trous legers. L'ajustement des estimations theoriques aux energies des transitions observees a conduit a la determination precise des decalages de bandes aux interfaces inas/inp et inas/gaas et a l'obtention du coefficient de segregation lie a la repartition de l'indium dans les multi-puits d'inas/gaas. La modelisation numerique des resultats experimentaux a necessite la mise en uvre de modeles incluant de facon satisfaisante les effets conjugues des fortes contraintes et des couplages entre bandes. En particulier, nous avons mis au point une procedure de calcul permettant la determination correcte des etats de valence dans un puits quantique contraint et incluant le couplage entre la bande des trous legers et la bande spin-orbite qui intervient par interaction #k. #p via d'autres bandes eloignees
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Hapke-Wurst, Isabella. « Resonanter Magnetotransport durch selbstorganisierte InAs-Quantenpunkte ». [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965263339.
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Dvorak, Martin W. « InAs/AlSb heterostructure field-effect transistors ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24125.pdf.
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Devenson, Jan. « Trumpabangiai InAs/AlSb kvantiniai kaskadiniai lazeriai ». Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20101102_153721-11993.
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Disertaciniame darbe nagrinėjamas InAs/AlSb medžiagų sistemos panaudojimas trumpabangių tarppajuostinių lazerių kūrimui. Buvo išplėtota molekulinių pluoštelių epitaksijos technologija, leidžianti auginti daugiaperiodines neįtemptas InAs/AlSb heterosandūras su mažu 1-2 atominių sluoksnių šiurkštumu. Buvo parodyta, jog InAs/AlSb medžiagų sistema yra tinkama kurti trumpabangiams kvantiniams kaskadiniams lazeriams, veikiantiems žemiau 4 µm bangos ilgio ribos. Buvo ištirtas kvantinių kaskadinių lazerių, turinčių tiek plazmoninius bangolaidžius su stipriai legiruotais InAs apdariniais sluoksniais, tiek ir mažo periodo InAs/AlSb supergardelių bangolaidžius, veikimas bei jų įtaka prietaiso parametrams. Šie sprendimai dėl bangolaidžių bei tolimesni aktyviosios terpės patobulinimai, naudojant piltuvėlio formos injektorių, leido sukurti didelio našumo prietaisus, galinčius veikti iki 420 K temperatūros, esant 3,3 µm bangos ilgio emisijai, ir pasiekti maksimalią optinę galią siekiančią 1 W kambario temperatūroje. Šios inovacijos leido sukurti ir InAs/AlSb kvantinį kaskadinį lazerį, emituojantį ~2,6 µm bangos ilgio spinduliuotę šiai dienai tai yra trumpiausią bangos ilgį spinduliuojantis tokio tipo prietaisas pasaulyje.Application of InAs/AlSb materials system for development of short-wavelength quantum cascade lasers is explored. Molecular beam epitaxy (MBE) technology allowing to grow multiperiodical unstrained InAs/AlSb heterostructures with roughness of 1-2 monolayers is developed. It is demonstrated that InAs/AlSb materials system is well-suitable for development of short-wavelength quantum cascade lasers operating below 4 µm wavelength. Lasers containing plasmon-enhanced waveguides as well as the short period InAs/AlSb superlattices as waveguides were designed, MBE-grown and studied. The effect of waveguide properties on the device parameters is revealed. Usage of these waveguides and innovations in laser active region introducing “funnel” injector allowed one to reach operation temperature 420 K at the emission wavelength of 3.3 µm. The obtained optical peak power exceeded 1 W per facet. The room temperature operation has been obtained at wavelength below 3 µm. As for wavelength range, applying the new active region design strategy and the short period InAs/AlSb superlattice spacers InAs based quantum cascade lasers emitting at the wavelengths as short as 2.63 µm were developed, which is today the shortest emission wavelength of the operation of semiconductor lasers based on the intersubband transitions.
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Deacon, Russell. « Magnetotransport studies of InAs/GaSb superlattices ». Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427872.
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Chang, Willy. « Superconducting Proximity Effect in InAs Nanowires ». Thesis, Harvard University, 2014. http://nrs.harvard.edu/urn-3:HUL.InstRepos:13070025.
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First discovered by Holm and Meissner in 1932, the superconducting proximity effect has remained a subject of experimental and theoretical interest. In recent years, it has been proposed that proximity effect in a semiconductor with large g-factor and spin-orbit coupling could lead to exotic phases of superconductivity. This thesis focuses on proximity effect in one of the prime semiconductor candidates -- InAs nanowires.
The first set of experiments investigates the superconducting phase-dependent tunneling spectrum of a proximitized InAs quantum dot. We observe tunneling resonances of Andreev bound states in the Kondo regime, and induce quantum phase transitions of the quantum dot ground state with gate voltage and phase bias -- the latter being the first experimental observation of its kind. An additional zero-bias peak of unknown origin is observed to coexist with the Andreev bounds states.
The second set of experiments extends upon the first with sharper tunneling resonances and an increase in the device critical field. By applying an external magnetic field, we observe spin-resolved Andreev bound states in proximitized InAs quantum dots. From the linear splitting of the tunneling resonances, we extract g-factors of 5 and 10 in two different devices.
The third set of experiments utilizes a novel type of epitaxial core-shell InAs-Al nanowire. We compare the induced gaps of these nanowires with control devices proximitized with evaporated Al films. Our results show that the epitaxial core-shell nanowires possess a much harder induced gap -- up to two orders of magnitude in sub-gap conductance suppression as compared to a factor of five in evaporated control devices. This observation suggests that roughness in S-N interfaces plays a crucial role in the quality of the proximity effect.
The fourth set of experiments investigates the gate-tunability of epitaxial half-shell nanowires. In a half-shell nanowire Josephson junction, we measure the normal state resistance, maximum supercurrent, and magnetic field-dependent supercurrent interference patterns. The gate dependences of these independent experimental parameters are consistent with one another and indicate that an InAs nanowire in good ohmic contact to a thin sliver of Al retains its proximity effect and is gate-tunable.Physics
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Vaughan, Thomas Alexander. « Magneto-optics of InAs/GaSb heterostructures ». Thesis, University of Oxford, 1995. http://ora.ox.ac.uk/objects/uuid:52b3d4c8-04f2-4ee8-b5a5-382934807722.
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The optical properties of InAs/GaSb heterostructures under applied magnetic fields are studied in experimental and theoretical detail. The InAs/GaSb system is a type-II "crossed-gap" system, where the valence band edge of GaSb lies higher in energy than the conduction band edge of InAs. This leads to a region of energy above the InAs conduction band where conduction and hole states mix. Thin-layer superlattices remain semiconducting due to confinement effects, but thick-layer superlattices experience charge transfer which leads to intrinsic carrier densities approaching 1012 cm-2 per layer. Existing multi-band modeling techniques based on the k·p formalism are discussed, and a method of solving superlattice band structure (the "momentum-matrix" technique) is presented. The quantizing effects of the superlattice layers and applied magnetic fields are investigated, and the selection rules for optical transitions are derived. Standard cyclotron resonance (CR) is used to study effective masses in InAs/GaSb structures. The heavy hole mass is found to be strongly orientation-dependent, with a mass in the [111] orientation reduced 25% from the [001] mass. The electron mass is found to be roughly isotropic with respect to growth orientation, but shows variation with the InAs width due to quantum confinement effects. CR of InAs/GaSb heterojunctions display hitherto unexplained oscillations in linewidth, intensity, and effective mass. A model is proposed which explains the oscillations, based on the intrinsic nature of the InAs/GaSb system. CR is performed on an InAs/GaSb heterojunction using a free-electron laser, where due to the high intensities (on the order of MW/cm2) the absorption process saturates. This saturation allows for a determination of non-radiative relaxation lifetimes, and through the energy dependence of these lifetimes the magnetophonon effect is observed, allowing a direct measurement of LO-phonon-assisted energy relaxation rates. Coupling is introduced into the standard CR experiment, either by tilting the sample with respect to the magnetic field, or by applying a metal grating to the surface. These coupled CR experiments have striking qualitative results which allow for determination of subband separation energies and coupling matrix elements. Photoconductivity experiments are performed on thin-layer (semiconducting) superlattices, showing optical response at far-infrared wavelengths (5-20 μm). The results are compared with k·p calculations. One sample is processed for vertical transport, in which conduction occurs perpendicular to the superlattice layers. Strong optical response from this sample indicates the viability of InAs/GaSb-based far-infrared detectors. The momentum-matrix technique is used to predict optimum parameters for semiconducting superlattices with band gaps in the far-infrared. Semimetallic structures are studied via a multi-band self-consistent model, with results corroborating with and extending previous work. Intrinsic structures under applied magnetic field are modeled theoretically for the first time.
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Tutu, F. K. K. « InAs/GaAs quantum dot solar cells ». Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1430283/.
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Self-assembled III-V quantum dots (QDs) have been intensely studied for potential applications in solar cell (SC) devices in order to increase power conversion efficiency. Due to their quantum confinement of carriers, QDs have been proposed as a means of implementing the intermediate band solar cell (IBSC). The IBSC concept is characterised by in an increase in photocurrent and a preservation of output voltage, resulting from an enhanced sensitivity to the solar spectrum. The work reported in this thesis is concerned with the development of InAs QDs in GaAs p-i-n solar cell structures, with the aim of realising of an IBSC. The work involves the design, epitaxial growth by molecular beam epitaxy (MBE), device processing and characterisation of the QDSCs. This thesis first investigates InAs/InGaAs dot-in-a-well (DWELL) solar cell structures grown under different conditions. The use of a high-growth-temperature GaAs spacer layers is demonstrated to significantly enhance the performance of the multilayer DWELL solar cells. Threading dislocations were observed for a 30-layer QD structure with GaAs spacer layers grown at a low temperature (510 oC). By growing the GaAs spacer layer at a higher temperature (580 oC), the formation of threading dislocations were suppressed, resulting in enhanced optical properties. The thesis then goes on to address the main challenges facing QD IBSCs, that is, the reduction in open-circuit voltage and the lack of significant increase in short-circuit current. To eliminate the wetting layer and enhance the open-circuit voltage of the QD solar cell, an AlAs cap layer technique was used. This resulted in an enhancement of the open-circuit voltage of a 20-layer InAs/GaAs QDSC from 0.69 V to 0.79 V. Despite a slight reduction in short-circuit current, for the QDSC with AlAs cap layer, the enhancement in the open-circuit voltage was enough to ensure that its efficiency is higher than the QDSC without AlAs cap layers. In an attempt to enhance the short-circuit current, an antimony-mediated growth approach was used to grow high-density QDs. After optimisation of the growth temperature and InAs coverage, a very high in-plane QD density of 1 1011 cm-2 was achieved by applying a few monolayers of antimony prior to QD growth. Compared with a reference QDSC without the incorporation of antimony, the high-density QDSC demonstrates a distinct improvement in short-circuit current from 7.4 mA/cm2 to 8.3 mA/cm2. This result shows that a significant increase in short-circuit current could potentially compensate for the drop in open-circuit voltage observed in InAs/GaAs QD solar cells. Ongoing work on the development of QDSCs with both AlAs capping and antimony-mediated growth have resulted in the simultaneous elimination of the wetting layer and increase in QD absorption in a single device. Overall, the studies in this thesis present important implications for the design and growth of InAs/GaAs QD solar cell structures for the implementation of IBSCs.
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Tahraoui, Abbès. « Elaboration d'hétérostructures à base d'antimoniures : Etude et optimisation de la formation des interfaces InAs/GaSb et GaSb/InAs ». Montpellier 2, 1998. http://www.theses.fr/1998MON20171.
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Djukic, Uros. « Croissance, structure atomique et propriétés électroniques de couches minces de Bismuth sur InAs(100) et sur InAs(111) ». Thesis, Cergy-Pontoise, 2015. http://www.theses.fr/2015CERG0760/document.
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L'émergence d'une une nouvelle classe de matériaux, des isolants topologiques, a stimulé un vaste champ de recherche. Bismuth, un élément du groupe V du tableau périodique, est un des ingrédients clé d'une famille d'isolants topologiques. Pour des applications dans la technologie des composants électroniques, il est essentiel de maîtriser la préparation des matériaux en couches minces. Dans ce travail de thèse, nous avons étudié la croissance et la structure électronique de bismuth sur les surfaces (100) et (111) de semi-conducteur III-V InAs.Déposition de Bi sur la surface InAs(100) résulte en une auto-organisation de Bi qui forme des lignes de taille atomique. On montre que le bismuth interagit extrêmement faiblement avec la surface car la structure d'origine de la surface propre de l'InA(100) reste intacte. L'étude de la bande valence montre la présence d'états résonants fortement dépendants de l'énergie de photons et de la polarisation de la lumière, en cohérence avec la structure quasi unidimensionnelle de la surface.La spécificité de la surface InAs(111) est qu'elle a deux terminaisons différentes: par In, (face A) et par As, (face B). Les deux faces présentent des reconstructions différentes. Par la photoémission des niveaux de coeur nous avons montré une différence de réactivité chimique entre les faces A et B. La croissance de Bi sur la face A résulte en un monocristal de haute qualité pour les films à partir de 10 monocouches. Par contre, lors du dépôt de premières couches, la face B montre une croissance en îlots et un bon monocristal est obtenu seulement pour des films d'au moins de 50 monocouches.Pour la même face, A ou B, nous avons observé des différences de croissance plus subtiles entre les surfaces préparées soit par le bombardement ionique et des recuits soit par l'épitaxie par jets moléculaires.La photoémission résolue en angle a permit de caractériser la dispersion des bandes dans les films de Bi. La dispersion est tout à fait comparable au cristal massif de Bi. La dernière étape consistait à étudier la structure électronique d'un monocristal de Sb déposé sur le film de Bi.Les surfaces propres de InAs(111)A et InAs(111)B présentent une courbure de bande qui résulte en formation d'une couche d'accumulation d'électrons. En déposant le Bi sur ces surfaces, la couche d'accumulation est préservée, elle est même amplifié, car Bi agit comme le donneur dans l'InAs.La couche d'accumulation se traduit par un confinement quantique des électrons, mesurable par la photoémission résolue en angle.Mots clés :Structure électronique de surface, ARPES, semimétal, courbure de bande, Gaz-2D, Bismuth, Sb, InAs(111)A, InAs(111)B, puits quantique, surface Fermi, couches mincesA new class of material is coming up, Topological Insulators, have opened a wide field of research. Bismuth, an element of group V of periodic table, is one of the key ingredient of this Topological Insulators family. With the aim of improving technological applications, especially the electronic compounds, it is of most importance to control the preparation of thin films materials. Within this Phd work, we studied the growth and Bismuth electronic structure on (100) and (111) semiconductor III-V InAs surfaces.Bi deposition on InAs(100) surface result of a Bi self-assembly which forms lines at atomic scale. We show Bi interact extremely weakly with the surface because the beginning structure of clean InAs(100) surface stay unharmed. The study of valence band sheds light on the existence of resonant states strongly photon energy dependent and also depend on the light polarization, consistent with almost one dimensional structure surface.InAs(111) surface specific feature is that it has both surface ending different : In ending, (face A) and As ending, (face B). The both faces pointed out distinguishable reconstructions. By the core-level photoemission we identified a chemical reactivity difference taking place between A and B faces. Bi growth on A-face tend to be a high quality monocrystal for those films from a thickness of 10 monolayers. On the other hand, during the deposition of first layers, the B-face show an island growth and a good monocrystal is obtained only available for films with 50 monolayers at least.For the same face, A or B, we have seen some growth discrepancies more subtle between prepared surfaces either by ionic bombardment and annealing (IBA) either by molecular beam epitaxy (MBE).The angular resolved photoemission allowed to identify the band dispersion inside of this Bi films. The dispersion is absolutely relative to the bulk Bi crystal. The final step involved the study of Sb monocrystal electronic structure deposited onto Bi film.Clean InAs(111)A and InAs(111)B surfaces indicate a band bending which result in the accumulation electron charge formation. With depositing Bi onto these surfaces, the accumulation layer would be kept, it is also increased, given that Bi acts as a donor-like in InAs. The accumulation layer is characterized by an electron quantum confinement, measurable by angle resolved photoemission.Keywords:Electronic structure surface, ARPES, semimetal, band bending effect, 2DEG, Bismuth, Sb, InAs(111)A, InAs(111)B, quatum wells, Fermi surface, thin films
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Hammerschmidt, Thomas. « Growth simulations of InAs-GaAs quantum dots ». [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981194370.
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Schramm, Andreas. « Selbstorganisierte InAs-Quantenpunkte Eigenschaften, Modifizierung und Emissionsprozesse / ». [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=984308512.
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Kailuweit, Peter. « Untersuchung der Valenzbandzustände selbstorganisiert gewachsener InAs-Quantenpunkte ». Waabs GCA-Verl, 2005. http://deposit.d-nb.de/cgi-bin/dokserv?id=2844649&prov=M&dok_var=1&dok_ext=htm.
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Kailuweit, Peter. « Untersuchung der Valenzbandzustände selbstorganisiert gewachsener InAs-Quantenpunkte / ». Waabs : GCA-Verl, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?id=2844649&prov=M&dok_var=1&dok_ext=htm.
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Devenson, Jan. « InAs/AlSb short wavelength quantum cascade lasers ». Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20101102_153710-37964.
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Application of InAs/AlSb materials system for development of short-wavelength quantum cascade lasers is explored. Molecular beam epitaxy (MBE) technology allowing to grow multiperiodical unstrained InAs/AlSb heterostructures with roughness of 1-2 monolayers is developed. It is demonstrated that InAs/AlSb materials system is well-suitable for development of short-wavelength quantum cascade lasers operating below 4 µm wavelength. Lasers containing plasmon-enhanced waveguides as well as the short period InAs/AlSb superlattices as waveguides were designed, MBE-grown and studied. The effect of waveguide properties on the device parameters is revealed. Usage of these waveguides and innovations in laser active region introducing “funnel” injector allowed one to reach operation temperature 420 K at the emission wavelength of 3.3 µm. The obtained optical peak power exceeded 1 W per facet. The room temperature operation has been obtained at wavelength below 3 µm. As for wavelength range, applying the new active region design strategy and the short period InAs/AlSb superlattice spacers InAs based quantum cascade lasers emitting at the wavelengths as short as 2.63 µm were developed, which is today the shortest emission wavelength of the operation of semiconductor lasers based on the intersubband transitions.Disertaciniame darbe nagrinėjamas InAs/AlSb medžiagų sistemos panaudojimas trumpabangių tarppajuostinių lazerių kūrimui. Buvo išplėtota molekulinių pluoštelių epitaksijos technologija, leidžianti auginti daugiaperiodines neįtemptas InAs/AlSb heterosandūras su mažu 1-2 atominių sluoksnių šiurkštumu. Buvo parodyta, jog InAs/AlSb medžiagų sistema yra tinkama kurti trumpabangiams kvantiniams kaskadiniams lazeriams, veikiantiems žemiau 4 µm bangos ilgio ribos. Buvo ištirtas kvantinių kaskadinių lazerių, turinčių tiek plazmoninius bangolaidžius su stipriai legiruotais InAs apdariniais sluoksniais, tiek ir mažo periodo InAs/AlSb supergardelių bangolaidžius, veikimas bei jų įtaka prietaiso parametrams. Šie sprendimai dėl bangolaidžių bei tolimesni aktyviosios terpės patobulinimai, naudojant piltuvėlio formos injektorių, leido sukurti didelio našumo prietaisus, galinčius veikti iki 420 K temperatūros, esant 3,3 µm bangos ilgio emisijai, ir pasiekti maksimalią optinę galią siekiančią 1 W kambario temperatūroje. Šios inovacijos leido sukurti ir InAs/AlSb kvantinį kaskadinį lazerį, emituojantį ~2,6 µm bangos ilgio spinduliuotę šiai dienai tai yra trumpiausią bangos ilgį spinduliuojantis tokio tipo prietaisas pasaulyje.
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Poulter, Andrew James Langdale. « Magneto-optical studies of InAs/GaSb heterostructures ». Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299507.
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Khym, Sungwon. « Magnetotransport studies of semimetallic InAs/GaSb structures ». Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325145.
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Symons, David Malcolm. « Magnetotransport studies on new GaSb/InAs heterostructures ». Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260114.
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Petchsingh, Cattleya. « Cyclotron resonance studies on InAs/GaSb heterostructures ». Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270653.
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Koletsios, Evangelos. « GaAs/InAs multi quantum well solar cell ». Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/27856.
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In this thesis, Silvaco software is used to form a precise, well-controlled reliable, and inexpensive solar-cell structure using quantum wells. Successful results will allow the exploitation of most of the advantages of quantum-well systems. This challenging research represents the first time that Silvaco simulation software has been used in the design of such a solar cell. This research field is promising because of the potential to increase the attainable energy efficiency of solar photon conversion, due to tunable bandgaps, which can absorb most of the solar spectrum, which conventional single-layer crystalline solar cells cannot do. The ultimate goal is the assembly of a quantum-well layer. A theoretical infinite-layer cell can reach an efficiency of 86% (constrained by thermodynamical limits). Quantum wells can reach 65%+ when a multilayer cell has reached 49%, and it is very expensive to build.
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Rawle, Jonathan Leonard. « X-ray scattering from InAs quantum dots ». Thesis, University of Leicester, 2005. http://hdl.handle.net/2381/27586.
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This thesis addresses one of the major outstanding problems in the study of self-assembled InAs quantum dots (QDs): their physical profile after deposition of a capping layer and post-growth processing. The optical properties of QDs depend critically on the shape, composition and strain profile, yet these parameters are inaccessible to most experimental techniques once the dots are buried. Data from various x-ray scattering experiments are presented here, along with a novel approach to simulating diffuse scattering using an atomistic model based on Keating energy minimisation. The size and position of the diffuse scattering on the low-Q side of the Bragg peak, which are strongly influenced by the shape and composition of the QDs, has been used to determine that the QDs are truncated pyramids with a diagonal base length of 28 nm, with their edges aligned along the [100] and [010] directions. The composition profile varies from pure InAs at the top to 40-60% InAs at the base. These properties all agree with recent cross-sectional scanning tunnelling microscopy (X-STM) measurements by Bruls et al. It was shown that post-growth annealing causes a reduction in the In content of the QDs, primarily by diffusion from the base of the dot into the wetting layer. Grazing incidence small angle x-ray scattering (GISAXS) measurements have been made from samples of QDs produced with varying growth interruptions (GI) before deposition of the capping layer. The QDs were found to be highly diffuse. After a GI, the dots have been shown to change shape anisotropically, with two facets becoming sharper. An investigation of the use of resonant scattering to study buried QDs has shown that the method of contrast variation is of limited use for enhancing the measurement of diffuse features away from the Bragg peak. It is unsuitable for the study of buried nanostructures.
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Xu, Xiulai. « InAs quantum dots for quantum information processing ». Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615012.
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Lima, Tiago de Almeida Cerqueira. « Modelos INAR e RCINAR, estimação e aplicação ». Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/45/45133/tde-10062013-230800/.
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Neste trabalho primeiramente apresentamos um modelo para uma sequência estacionária de valores inteiros (processo de contagem) autoregressivo de ordem p (INAR(p)). Depois disso, mos- traremos uma extensão desse processo, chamado modelo autoregressivo inteiro com coeficientes aleatórios (RCINAR(p)) . Para ambos os modelos, apresentamos suas propriedades assim como diferentes métodos de estimação de seus parâmetros. Os resultados da simulação e comparação dos estimadores são mostrados. Finalmente os modelos são aplicados em dois conjuntos de dados reais: Número mensal de empresas em falência; Número mensal de consultas no bureau de crédito.At this work we first present a model for stationary sequence of integer-valued random variables (counting process) referred to as the integer-valued autoregressive of order p (INAR(p)) process. Af- ter this we show an extension of this process, called random coefficient integer-valued autoregressive process (RCINAR(p)). For both models we present its properties as well as different methods of estimation of its parameters. Simulation results and the comparison of the estimators are reported. Finally the models are applied to two real data sets: monthly number of companies with bankruptcy; monthly number of enquiries in credit bureau.
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Miska, Patrice. « Propriétés optiques des boîtes quantiques InAs/Inp ». Rennes, INSA, 2003. http://www.theses.fr/2003ISAR0005.
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Puangmali, Theerapong. « Electronic and optical properties of InAs nanocrystals ». Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/1169/.
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An atomistic pseudopotential method is used to investigate the electronic and opti- cal properties of spherical InAs nanocrystals. Our calculated interband (valence-to- conduction) absorption spectra reproduce the features observed experimentally both qualitatively and quantitatively. The results relative to intraband (valence-to-valence and conduction-to-conduction) absorption successfully reproduce the recently measured photoinduced absorption spectra, which had so far been addressed only qualitatively. They exclude the hypothesis of a thermal activation process between dot-interior delocalised hole states to explain the temperature dependence observed experimentally. Furthermore, based on the agreement of our data with the experimental valence inter- sublevel transitions and the almost complete overlap of the latter with STM measure- ments, we question the simplistic attribution of the observed STM peaks obtained for negative bias. Motivated by the excellent agreement of our calculated results with the STM, PLE and PIA spectra, we therefore extend our knowledge to a detailed theoretical investigation of the electronic structure and optical properties of InAs nanocrystals at the transition from spheres to rods. We predict that despite the qualitative similarity of both intra- and inter-band optical spectra, for NCs with R > 15 ̊A even slight elongations should result in shifts of the order of hundreds of meV in the spacings between STM peaks measured ii Abstract iii in the positive bias regime, in the position of the intra-band absorption peaks associated with transitions in the conduction band and in the separation between the first and the fifth peak in PLE experiments. Our results suggest that, based on the spectroscopic data, it should be possible to discriminate between spherical and elongated NCs with aspect ratios of length over diameter as small as 1.2. Indeed our results suggest that many nominally spherical experimental samples contained a large fraction of slightly elongated structures. Additionally, the atomistic pseudopotential approach is also applied to a study of the electronic and optical properties of InAs quantum rods as a function of increasing length- to-diameter ratio. We show that, as the aspect ratio increases, energy levels cross in both conduction and valence bands, reflecting their different dependence on confinement along a specific direction. Unlike in CdSe and InP quantum rods, however, the position of the crossover between highest occupied molecular orbitals with different symmetries is found to be size-dependent and the value of the aspect ratio at the crossing to increase with the rod diameter. We find that the level crossings at the top of the valence band are crucial to explain the evolution with elongation of all optical properties in these systems. Their transformation from 0- to quasi-1-dimensional structures is characterised by a common monotonic behaviour of band gap, Stokes shift, degree of linear polarisation and radiative lifetime, closely linked to the variation with aspect ratio of the electronic structure of the nanocrystal valence band edge. This characteristic feature was not observed in elongated CdSe structures, whose optical properties exhibited instead a distinctive non-monotonic evolution with length, with a turning point associated with a crossover at the top of the valence band, similar to that found here between states with σ and π symmetries.
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PEREIRA, Marcelo Bourguignon. « Modelos inar sazonais e de raízes unitárias ». Universidade Federal de Pernambuco, 2011. https://repositorio.ufpe.br/handle/123456789/6259.
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Previous issue date: 2011Conselho Nacional de Desenvolvimento Científico e Tecnológico
Séries temporais de contagem têm chamado a atenção pela importância em aplicações nas diversas áreas de conhecimento. Os processos estocásticos usuais assumem que as marginais são contínuas e, em geral, não são adequados para modelar séries de contagem. Portanto, surge a necessidade de investigar metodologias apropriadas para séries temporais com distribuições marginais discretas. Em particular, o estudo da presença de raízes unitárias e o comportamento sazonal do processo de valores inteiros motivam uma vertente de pesquisa de grande interesse para aplicações práticas e são os principais objetivos desta pesquisa. Nesse contexto, apresentamos o teste de Dikey & Fuller (1979) e verificamos o comportamento do teste, através de ensaios de Monte Carlo, em processos autorregressivos de valores inteiros de ordem um, quando o processo apresenta raiz unitária. Os pontos críticos empíricos da estatística de teste do teste de Dickey-Fuller, para vários valores do percentil α, são calculados quando o teste é utilizado em processos INAR(1) com erros Poisson, para diversos valores do parâmetro λ. Comparações entre a utilização do teste de Dickey-Fuller em processos com marginais contínuas e discretas também são abordadas. No que tange à sazonalidade em processos de contagem, é proposto um modelo de valores inteiros com estrutura sazonal baseado no modelo de Al-Osh & Alzaid (1987). As principais propriedades do modelo proposto são derivadas, tais como os momentos, a função de autocovariância e a função de autocorrelação. Ensaios de Monte Carlo são realizados para comparar os vícios e erros quadráticos médios de três estimadores para os parâmetros do modelo proposto. Como motivação do uso da metodologia sugerida, a série do índice da qualidade do ar da cidade de Cariacica-ES foi analisada
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Anufriev, Roman. « Optical properties of InAs/InP nanowire heterostructures ». Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0133/document.
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Ce travail de thèse porte sur l’étude des propriétés optiques de nanofils InP et d’hétérostructures nanofils InAs/InP épitaxiés sur substrat silicium. Ce travail de thèse a été réalisé principalement dans le cadre du projet ANR «INSCOOP»This thesis is focused upon the experimental investigation of optical properties of InAs/InP NW heterostructures by means of photoluminescence (PL) spectroscopy. First, it was demonstrated that the host-substrate may have significant impacts on the optical properties of pure InP NWs, as due to the strain, created by the difference in the LTECs of the NWs and the host-substrate, as due to some other surface effects. Next, the optical properties of such nanowire heterostructures as quantum rod (QRod) and radial quantum well (QWell) NWs were investigated. The features of obtained spectra were explained using theoretical simulation of similar NW heterostructures. The polarization properties of single InP NWs, InAs/InP QWell-NWs, InAs/InP QRod-NWs and ensemble of the InAs well ordered NWs were studied at different temperatures. Further, we report on the evidences of the strain-induced piezoelectric field in WZ InAs/InP QRod-NWs. Finally, PL QE of NW heterostructures and their planar analogues are measured by means of a PL setup coupled to an integrating sphere. In general, the obtained knowledge of the optical and mechanical properties of pure InP NWs and InAs/InP NW heterostructures will improve understanding of the electrical and mechanical processes taking place in semiconductor NW heterostructures and will serve for the fabrication of future nanodevice applications
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Naumann, Werner. « Ultrahochvakuum-Präparation und Charakterisierung von InAs(100)-Oberflächen ». [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=964176947.
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Schulz, Stephan. « Kapazitäts- und Kapazitätstransientenspektroskopie an selbstorganisiert gewachsenen InAs-Quantenpunkten ». [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975631314.
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Wrålsen, Arnt Joakim. « X-ray diffraction studies of InAs/GaAs heterostructures ». Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18348.
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Intermediate band solar cells (IBSC) is a proposed new type of solar cell device that has an intermediate energy band in the band gap. One possible implementation of IBSCs is by using arrays of nano-sized semiconductor particles known as quantum dots (QDs). InAs QDs can be grown on GaAs by using molecular beam epitaxy (MBE). As a part of this growth process, an InAs wetting layer (WL) is formed on which the InAs QDs grow. One possible method of determining the WL thickness is by using x-ray diffraction (XRD), which is a non-destructive analysis technique used to extract information about the structure and composition of crystalline thin films.An InAs/GaAs bilayer sample grown by MBE was investigated. This sample was grown without rotation, meaning the thicknesses of the deposited layers are expected to exhibit a gradient across the sample. Based on the geometry of the MBE machine, the variation in deposited thicknesses across the sample was estimated to be ±3.4% for InAs and ±4.2% for GaAs. XRD rocking curve measurements were performed around the 004 reflection in thirteen different locations on this sample. LEPTOS software was used to simulate XRD curves, and these simulations were fitted to the XRD measurements by varying the thicknesses of the simulated InAs and GaAs layers. It was found that the GaAs thicknesses across the sample varied as expected, while the variation in InAs thicknesses was much larger than expected. It was also found that the measured thicknesses of the InAs layer were significantly thinner than the nominal value. This is a strong indication that there are QDs on the sample, and that only the WL of the QDs contributes to the x-ray curve.LEPTOS was also used to simulate several cases of alloying of an InAs/GaAs bilayer. It was found that if the entire InAs layer is segregated into an InAs/GaAs alloy, this causes the diffraction peaks to weaken as the InAs/GaAs interfaces become less abrupt. It was also found that intermixing causes a significant change in the XRD curve because the amount of GaAs in the InAs/GaAs bilayer structure increases.
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Baisitse, Tshepiso Revonia. « Characterisation of InAs-based epilayers by FTIR spectroscopy ». Thesis, Nelson Mandela Metropolitan University, 2007. http://hdl.handle.net/10948/474.
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This study focuses on the characterization of InAs and InAs1-xSbx epitaxial layers by infrared reflectance and transmittance spectroscopy and Hall measurements. Reflectance measurements were performed in order to obtain the dielectric parameters and to extract from these information about the electrical properties (mobility and carrier concentration) of this important III-V material system. The transmittance measurements were used to determine the bandgap of InAsSb. Infrared reflectivity and transmittance measurements were performed in the wavelength range 200 – 2000 cm-1 on InAs and InAsSb layers grown on three types of substrates. A classical two oscillator model that takes into account both the free carriers and the lattice, was used to analyse the reflectance data using the BMDP® computer curve fitting software. The dielectric parameters and the electrical properties (carrier concentration and mobility) were extracted from the simulations. Due to the low free carrier concentration in the epitaxial structures, the plasma resonance frequency (ωp) values obtained from the simulations of reflectance spectra measured above 200 cm-1, were in the order of 20-30 cm-1. These low values were confirmed by direct measurements of ωp in reflectance spectra obtained in the range 15-200 cm-1. The simulated carrier concentration and mobility values determined optically were compared to the values determined by Hall measurements at room temperature and previously reported values by other researchers. The simulated values obtained were in reasonable agreement with the Hall values. The simulated and measured carrier concentrations obtained for InAs layers were significantly higher than the intrinsic carrier concentration for InAs at room temperature, indicating notable concentrations of donors resulting from the growth process.
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Zhi, Dan. « Structure and composition of InAs/GaAs quantum dots ». Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414000.
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Barnes, Gareth William. « Solid source MBE growth of InAs / InP(001) ». Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409582.
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Howe, Patrick. « InAs/GaAs quantum dots for long wavelength applications ». Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415211.
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Daly, Matthew Stuart. « High pressure magnetotransport studies of InAs/GaSb heterostructures ». Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318520.
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Ng, Jen Teik. « Stacked self-assembled InAs/GaAs quantum dot lasers ». Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492128.
Texte intégralRésumé :
Stacked self-assembled binary InAs/GaAs quantum dot (00) lasers without strain reduction layers were grown using molecular beam epitaxy, operating near 1.3 I-lm under almost room temperature conditions. In order to fabricate the most efficient 00 laser, this work was divided into two major sections: the first part investigated the material properties of ODs, more specifically in stacked structures, and the second part was characterisation of the laser diode based on the optimised stack structure. Material characterisation investigations revealed that ODs grown from the self-assembly of nominally 2.73 monolayer thick InAs were suitable for near 1.3 I-lm emission. Due to the large size of the dots fabricated using this method, a high density of defects was observed in the stacked structure, reducing the quantum efficiency of the material. Optimisation work revealed that for a GaAs spacer layer thickness of 25 nm and 50 nm, the maximum number of stacking periods permissible before the onset of defect formation are three and eight periods respectively. Additionally, different growth conditions were investigated to understand their effects on the size and density of the nano-islands. Based on the results obtained from materials characterisation, two laser diodes were grown: a four- and three-stack structure with a GaAs spacer thickness of 25 nm, and 50 nm respectively. The use of such thick spacer layers was to decouple the strain between the adjacent dots and improve the crystallinity of the stacked structure. For the 25 nm case, the presence of defects in the structure, coupled with a high series resistance, lead to devices that were unable to demonstrate stimulated emission. By contrast, for the case of 50 nm, laser oscillation was observed under pulsed mode conditions up to 280 K, with a very high characteristic temperature (To) of 415 K from 100-200 K operation. Above that temperature To decreased rapidly to 45 K, indicating high losses in the cavity caused by defect processes. The results are very promising as there are many techniques not yet included that could enable the device to operate under continuous wave at room temperature.
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Cooper, L. J. « Magnetotransport studies of InAs/GaSb/AlSb-based structures ». Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597965.
Texte intégralRésumé :
A reliable procedure has been developed which facilitates the fabrication of low-leakage front and back gated lateral transport devices in which electrons and holes reside in adjacent layers. This gating permits the alteration of the electron and hole densities in such devices almost independently of one another. A simple processing technique has also been developed for resonant inter-band and hybrid inter/intra-bond tunnelling devices. In the absence of a barrier between the layers in which the charge resides, it is shown that the wavefunctions of electrons and holes hybridise, causing an energy gap to form in the dispersion relation of the hybrid particles. This manifests itself in lateral transport measurements as a resistance peak when the Fermi energy in the system is made to lie in this "gap" by the action of the gates. The resistance resonance is seen to disappear as a function of temperature and in-plane magnetic field. The results of a simple numerical model are shown to predict the broad features in the experimental data and allow the extraction of the magnitude of the energy gap in the system. Anomalous low-field positive magnetoresistance in an in-plane magnetic field is discussed in the context of wavefunction movement in the growth plane and the antilocalisation effects of asymmetry. In a perpendicular magnetic field, Landau levels are formed in the system and the transport shows Shubnikov-de Haas oscillations and quantum Hall plateaux originating from either carrier type. So-called "compensated Hall plateaux" are observed and the absence of a completely compensated "v=0" plateau is discussed. Magnetic field induced charge transfer between the electron and hole layers which depends on the inter-layer tunnelling is observed. Tilted magnetic field measurements are performed to extract the effective g-factor of the electrons in the system and the effect of electron-hole coupling on its value is discussed.
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ROSERO, JOSE EDUARDO RUIZ. « OPTICAL AND MORPHOLOGICAL CHARACTERIZATION OF INAS QUANTUM DOTS ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=26239@1.
Texte intégralRésumé :
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Se faz um estudo detalhado da produção de pontos quânticos de InAs crescidos sobre ligas de InGaAlAs que, por sua vez, são depositadas em substratos de InP de forma casada. Através da caracterização óptica e morfológica dos pontos quânticos obtém-se a dependência tanto da altura quanto da densidade dos pontos produzidos em função das condições de crescimento. Os pontos quânticos são produzidos em condições de crescimento variadas. A temperatura, o tempo de crescimento e a taxa de deposição são os parâmetros alterados de uma amostra para a outra. São utilizadas técnicas de microscopia de força atômica (AFM) e fotoluminescência (PL) para avaliar o efeito dos parâmetros de crescimento epitaxial sobre a qualidade óptica das estruturas obtidas, as alturas dos pontos quânticos nucleados, a homogeneidade e a densidade da distribuição resultante. É desenvolvida a otimização no processamento digital das imagens de AFM para obter melhores resultados em suas análises. São correlacionados e analisados os resultados obtidos em AFM como a altura e a densidade dos pontos quânticos e seus respectivos picos de emissão de PL. Finalmente foram feitas simulações dos níveis de energia dos pontos quânticos para correlacioná-las com os valores dos picos dos sinais de PL e as alturas dos pontos quânticos.
A detailed study is performed of the production of InAs quantum dots grown on InGaAlAs lattice matched to InP. Performing the optical and morphological characterization of the quantum dots the dependence of the height and density of the quantum dots with the growth conditions is obtained. The quantum dots were produced under different growth conditions. Temperature, growth time and growth rate were changed from one sample to another. We use atomic force microscopy (AFM) and photoluminescence (PL) techniques to evaluate the effect of the growth conditions on the optical quality of the obtained structures, as well as the quantum dots heights, their homogeneity and density distribution. Image processing of AFM images was optimized to allow better accuracy in the analysis of quantum dot height. The AFM results, such as quantum dots height and density, were related and analyzed with their respective PL emission. Finally, simulations of the quantum dots energy levels were performed to correlate them with the quantum dots height and PL signal.
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Santos, Nuno Miguel Duque da Silva. « Caracterização óptica de fios quânticos de InAs/InP ». Master's thesis, Universidade de Aveiro, 2007. http://hdl.handle.net/10773/2568.
Texte intégralRésumé :
Mestrado em Engenharia Física (2º ciclo)No presente trabalho é feito um estudo por fotoluminescência de heteroestruturas contendo camadas ou fios quânticos, crescidas por MBE, considerando fontes de excitação banda-a-banda e ressonante. As heteroestruturas foram sujeitas a irradiação com diferentes fluências de protões, 2,4 MeV, com o objectivo de estudar o efeito dos defeitos criados por este tratamento. Foi feita a dependência da fotoluminescência com a temperatura de modo a calcular as energias de activação e relacioná-las com as restantes energias: de fotão e de localização. Com o aumento das doses de irradiação ocorre uma diminuição da intensidade da emissão com origem em ambos os tipos de heteroestruturas quânticas consideradas. Esta diminuição é mais rápida para a temperatura ambiente comparativamente à temperatura do azoto líquido. Comparando os resultados obtidos com fios e com camadas quânticas conclui-se que existe uma maior resistência à irradiação por parte da primeira heteroestrutura. A utilização de uma fonte de excitação ressonante mostrou a menor influência na extinção da luminescência dos defeitos existentes na matriz de InP. A intensidade da fotoluminescência diminui com o aumento da temperatura em ambas as amostras, devido ao fornecimento de energia térmica aos portadores de carga confinados nos poços de potencial. No caso dos fios quânticos, verifica-se que para menores energias de fotão a energia de activação é maior o que é de esperar face à maior energia de localização dos portadores de carga. Com o aumento da temperatura o decaimento da intensidade da fotoluminescência com origem nos fios quânticos não é gradual. Verifica-se a existência de intervalos de temperatura onde ocorrem aumentos de intensidade que podem ser explicados pela passagem de portadores de carga entre os fios quânticos através da re-alimentação ou por efeito túnel assistido por fonões. ABSTRACT: In the present work, photoluminescence studies were made in samples with quantum wells and quantum wires, grown by MBE, using excitation sources that produce band-to-band and resonant with the potential wells excitations. In order to study the radiation damage into the heterostructures, the samples were irradiated with high energy (2.4 MeV), in different fluences. Measurements with band-to-band excitation were made in order to study the photoluminescence dependency with temperature to determine the activation energies and relate them with the photon and localization energies. With an increase of the proton fluence a decrease of the photoluminescence intensity for both types of heterostructures was observed. This quenching is faster at room temperature compared with liquid nitrogen temperature. The results showed an higher radiation resistance for quantum wires when compared to quantum wells. Same measurements were repeated using an infrared excitation, with a lower energy compared with InP energy gap. The results reveal that PL stability vs. irradiation fluence is negatively influenced by the capture of photoexcited carriers by radiation defects in the InP barrier. With resonant excitation, the results showed a minor influence of the defects in the InP matrix in the extinction of the photoluminescence. With the increase of the temperature, the intensity of the photoluminescence decreases due to the thermal excitation of the charge carriers. For quantum wires we observed higher activation energies for the components at lower energies as is expected due to the larger confining energies of the charge carriers inside the potential wells. With the increase of the temperature, the lowering of the photoluminescence intensity related to quantum wires happens in a non continuous way. In some temperatures interval’s a growth of the intensity is observed due to the deliverance of charge carriers by some quantum wires to other ones or by phonons assisted tunnel effect.
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Heidemeyer, Henry. « Konzepte zur gezielten lateralen Positionierung selbstordnender InAs Quantenpunkte ». [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11730041.
Texte intégral
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Lutz, Ina [Verfasser]. « Beweisvereitelung im Zivilprozess / Ina Lutz ». Frankfurt a.M. : Peter Lang GmbH, Internationaler Verlag der Wissenschaften, 2016. http://d-nb.info/112341999X/34.
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Lee, Devon Lovelle. « Pan Africanist Praxis Ina Belize ». Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/103648.
Texte intégralRésumé :
Pan Africanism is strategy that emerges through a history of surviving oppression, methodology to understand thought and action, and theory that tests findings against sociopolitical context. History, methodology and theory are used to develop the historical trajectory that responds to invasion, slavery, colonization and neocolonialism in Belize. As such, three manuscripts are offered to outline the historical narrative of Belizean Pan Africanism, autoethnographic insights for the study of Pan Africanism, and the sociopolitical context that contemporary Pan Africanism in Belize rises out of. Kurt Young defines Pan-Africanism as: "a fusing of affirmations of African identity with libratory efforts at the level of the masses (2009:7). The study and practice of Pan Africanism should therefore aligned in objectives and strategy to interrupt oppressive conditions that impact communities within the African Diaspora. This project, therefore, operationalizes scholar-activism in history, method and theory to outline strategic action and collective subversion as Pan Africanist Praxis in Belize.Doctor of Philosophy
White Colonizers invaded the shores of Africa, dislocating a people from their legacy and heritage. However, a strategy was formed to create a new legacy and heritage that broke the bondage of White supremacy that trapped Black bodies. From the enslaved that ran to forge a new path for their people, to those that shed blood for freedom, Pan Africanism has been a strategy that has incorporated thoughts of freedom into escape plans. This study builds a historical timeline for Pan Africanism in Belize, methodology for the study of Pan Africanism and an academic exploration of contemporary Pan Africanism in Belize. Pan Africanism as history, method and contemporary theory add to the body of knowledge by inserting Belize at the center of Pan Africanist theory and practice. The study and practice of Pan Africanism is aligned in objectives and strategy to interrupt historical and contemporary conditions that impact communities within the African Diaspora. This project, therefore, operationalizes scholar-activism in history, method and theory to outline strategic action and collective subversion as Pan-Africanist Praxis in Belize.