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Malins, David Brendan. "Ultrafast dynamics in InAs quantum dot and GaInNAs quantum well semiconductor heterostructures /." St Andrews, 2007. http://hdl.handle.net/10023/404.
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Wei, Zhifeng. "The optical response of semiconductor self-assembled quantum dots." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37098202.
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Hull, Peter J. "Synthesis and characterisation of quantum dots." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318760.
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Isaev, Leonid. "Spontaneous polarization effects in nanoscale systems based on narrow-gap semiconductors." Virtual Press, 2005. http://liblink.bsu.edu/uhtbin/catkey/1328116.
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In the framework of the two-band (Dirac) model, we analyze the electronic structure of nanoscale systems, based on narrow-gap semiconductors of Pb,_xSnx (Se, S) type. Themain attention is paid to the influence of properties of the surface, encoded in appropriate boundary conditions, on the size-quantized spectrum. From this point of view we consider two types of systems: spherical (quantum dots) and quasi one-dimensional (films).It is shown that the spectrum of the spherical quantum dot consists not only of usual size-quantized states, located above the gap edge, but also surface modes residing inside the gap. Such states manifest themselves in the far infrared part of the absorption spectrum, the measurement of which allows one to extract information about the dot surface.Next, we consider a film with the energy gap modulated in the <111> (growth) direction. It is shown that the spectrum of the infinite crystal possesses a supersymmetrical structure. The film boundaries, generally speaking, destroy the supersymmetry, i.e. size-quantized subbands turn out to be spin-split. However, there exists a class of boundary conditions that do not lift spin degeneracy. Physically, in this case there is no band mismatch at interfaces. Our central statement, therefore, consists of the following: even when the inversion symmetry is destroyed by the bulk inhomogeneity, the spin-splitting of the spectrum is a purely surface effect. This is illustrated on a simple example, when the energy gap varies linearly over the film width.Finally, we investigate the role of boundary conditions in the problem of scattering of spinor waves by a quantum dot. It is shown that the existence of surface states greatly modifies the scattering data; in particular, outgoing waves may turn out to be fully polarized.Department of Physics and Astronomy
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Angell, Joshua James. "SYNTHESIS AND CHARACTERIZATION OF CdSe-ZnS CORE-SHELL QUANTUM DOTS FOR INCREASED QUANTUM YIELD." DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/594.
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Quantum dots are semiconductor nanocrystals that have tunable emission through changes in their size. Producing bright, efficient quantum dots with stable fluorescence is important for using them in applications in lighting, photovoltaics, and biological imaging. This study aimed to optimize the process for coating CdSe quantum dots (which are colloidally suspended in octadecene) with a ZnS shell through the pyrolysis of organometallic precursors to increase their fluorescence and stability. This process was optimized by determining the ZnS shell thickness between 0.53 and 5.47 monolayers and the Zn:S ratio in the precursor solution between 0.23:1 and 1.6:1 that maximized the relative photoluminescence quantum yield (PLQY) while maintaining a small size dispersion and minimizing the shift in the center wavelength (CWL) of the fluorescence curve. The process that was developed introduced a greater amount of control in the coating procedure than previously available at Cal Poly.
Quantum yield was observed to increase with increasing shell thickness until 3 monolayers, after which quantum yield decreased and the likelihood of flocculation of the colloid increased. The quantum yield also increased with increasing Zn:S ratio, possibly indicating that zinc atoms may substitute for missing cadmium atoms at the CdSe surface. The full-width at half-maximum (FWHM) of the fluorescence spectrum did not change more than ±5 nm due to the coating process, indicating that a small size dispersion was maintained. The center wavelength (CWL) of the fluorescence spectrum red shifted less than 35 nm on average, with CWL shifts tending to decrease with increasing Zn:S ratio and larger CdSe particle size. The highest quantum yield was achieved by using a Zn:S ratio of 1.37:1 in the precursor solution and a ZnS shell thickness of approximately 3 monolayers, which had a red shift of less than 30 nm and a change in FWHM of ±3 nm. Photostability increased with ZnS coating as well. Intense UV irradiation over 12 hours caused dissolution of CdSe samples, while ZnS coated samples flocculated but remained fluorescent. Atomic absorption spectroscopy was investigated as a method for determining the thickness of the ZnS shell, and it was concluded that improved sample preparation techniques, such as further purification and complete removal of unreacted precursors, could make this testing method viable for obtaining quantitative results in conjunction with other methods.
However, the ZnS coating process is subject to variations due to factors that were not controlled, such as slight variations in temperature, injection speed, and rate and degree of precursor decomposition, resulting in standard deviations in quantum yield of up to half of the mean and flocculation of some samples, indicating a need for as much process control as possible.
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Park, Gyoungwon. "GaAs-based long-wavelength quantum dot lasers /." Digital version, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3008414.
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De, Amritanand Pryor Craig E. "Spin dynamics and opto-electronic properties of some novel semiconductor systems." [Iowa City, Iowa] : University of Iowa, 2009. http://ir.uiowa.edu/etd/352.
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Garrido, Mauricio. "Quantum Optics in Coupled Quantum Dots." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1273589966.
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Little, Reginald Bernard. "The synthesis and characterization of some II-VI semiconductor quantum dots, quantum shells and quantum wells." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/30573.
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Archer, Paul I. "Building on the hot-injection architecture : giving worth to alternative nanocrystal syntheses /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8520.
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Radovanovic, Pavle V. "Synthesis, spectroscopy, and magnetism of diluted magnetic semiconductor nanocrystals /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/8494.
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Wei, Zhifeng, and 魏志鋒. "The optical response of semiconductor self-assembled quantum dots." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37098202.
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Siegert, Jörg. "Semiconductor Quantum Dots Studied by Time-Resolved Luminescence Techniques." Licentiate thesis, KTH, Microelectronics and Information Technology, IMIT, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1789.
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In this thesis time-resolved photoluminescence spectroscopyis presented as a powerful tool to study the carrier dynamicsin various self-assembled quantum dot (QD) structures, whichare potentially attractive for device applications.
The experiments reveal the impact of proton irradiation onInGaAs QDs and comparable quantum wells. Nonradiativerecombination at defectsan important material parameterandmeasureof the structure optical qualityis found to play a much less important role for the QD samples.The superior radiation hardness can be explained as a result ofthe three-dimensional carrier confinement in QDs. Comparisonsbetween the structures show a decrease of photoluminescenceintensity for quantum wells but a slight increase for QDsirradiated at low to intermediate doses. This somewhatunexpected characteristic is described by an enhanced carriertransfer into the dots via the defects introduced in thematerial by the protons.
In a different structure carrier dynamics in spatiallyaligned of InAs QDs are investigated. Alignment along lines isachieved by misfit dislocations deliberately introduced in thesubstrate. Photoluminescence spectra of the dots exhibit muchsmaller inhomogeneous broadening than for the reference sampleas a result of an improved QD uniformity. Samples with varyingbuffer layer thicknesses were grown to study the influence ofdislocation related traps on the observed fastphotoluminescence decay. It is found that the fast carriertrapping is predominantly caused by point defects close to theQDs or at the QD/barrier interfaces.
Additional numerical simulations confirm the roles of thetwo independently acting traps in nonradiativerecombination.
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Guo, Bicheng. "Chemical synthesis and characterization of CdMnS and CdMnSe quantum dots /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202004%20GUO.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 63-66). Also available in electronic version. Access restricted to campus users.
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Bychkov, Andrey. "Quantum effects in artificial atoms." Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:93a68cff-9823-47d7-9505-b63806f1bbd4.
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This thesis contains a theoretical and experimental investigation of semiconductor quantum dots (artificial atoms). The first part presents a numerical study of spin effects in GaAs/AlAs modulation-doped quantum dots containing 0 to 50 electrons. A theoretical model is developed to calculate confinement potentials and ground-state electron density distributions using the Kohn-Sham local spin-density approximation. Spin polarization, defined as the difference between the up- and down-spin electron densities, is predicted to occur spontaneously in symmetric quantum dots and in quantum point contacts in the lowdensity regime as a result of electron exchange interactions. This spontaneous magnetization can be controlled by an applied gate voltage, which opens up applications in spintronics and provides a possible explanation for the non-integer quantization of the quantum point contact conductance. The second part describes experimental techniques to investigate photon-exciton coupling in InAs/GaAs self-assembled quantum dots. Two experiments on resonant excitation of a single quantum dot are proposed, whereby the quantum-dot emission is distinguished from resonant pump light by either photon bunching of collected photons with reference photons, or Michelson interferometry. The feasibility study of the proposed experiments shows that the photon-exciton coupling efficiency must be dramatically increased by putting the quantum dot inside an optical microcavity. Novel types of high-quality, low mode-volume semiconductor microcavities containing quantum dots are designed, fabricated, and studied on a newly built setup. We present the first results of photoluminescence studies of InAs quantum dots inside both GaAs single-defect square-lattice photonic-crystal slabs and GaAs/AlAs micropillars, and InAs artificial molecules formed by vertically coupled strain-assisted quantum dots. The results indicate the potential of these nanostructures for implementing resonant transfer of quantum information, developing quantum repeaters and entangled-photon sources, and studying QED effects in the strong-coupling regime.
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McGinnis, Brian Patrick. "Four-wave mixing and the study of optical nonlinearities in semiconductors and semiconductor quantum dots." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184890.
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This dissertation describes the study of various nonlinear optical effects in both bulk and quantum-confined semiconductors. Transverse effects in increasing absorption optical bistability are considered in bulk CdS for both single beam and wave mixing geometries. Measurement of the temporal response of BiI₃ quantum dots is described using degenerate four-wave mixing and explained theoretically. Finally, the experimental techniques developed to measure the one- and two-photon absorption coefficients of CdS quantum dots in glass are described along with the latest theoretical description and interpretation of the experimental spectra. The basic theory of increasing absorption optical bistability is presented along with experimental observation of this effect in CdS at low temperature. Transverse effects in increasing absorption optical bistability were observed in single beam experiments with CdS at low temperatures. The ring structures observed experimentally are explained theoretically. Degenerate four-wave mixing performed with this nonlinearity is theoretically shown to produce new scattering orders compared with a standard Kerr analysis. Experimental observation of these new scattering orders is presented. The temporal response of the nonlinearity in a solution of BiI₃ quantum dots in acetonitrile is determined using degenerate four-wave mixing. The independent contributions to the phase-conjugate signal are determined for both of the spatial gratings induced in the solution. The observed temporal responses indicated that a thermal mechanism was responsible for the nonlinearity. A theoretical analysis based on a thermal nonlinearity is presented which provides good agreement with the observed responses. The experimental techniques necessary to measure the one- and two-photon absorption coefficients of CdS quantum dots are described. The resultant measurements of quantum dot samples with microcrystallites ranging from 3.6 to 10.8 nm in diameter indicate no splitting of the energy levels associated with the hole. Theoretical spectra indicate this can be partially explained by the inclusion of Coulombic effects of the charged electron-hole pair.
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Cheng, Cheng. "Semiconductor colloidal quantum dots for photovoltaic applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:07baccd0-2098-4306-8a9a-49160ec6a15a.
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This thesis studies lead suphide (PbS) colloidal quantum dots and their photovoltaic applications. Different sizes of PbS QDs were synthesised and characterised using absorption spectroscopy and transmission electron microscopes. PbS QD Schottky junction devices were fabricated with AM1.5 power conversion efficiency up to 1.8 %. The Schottky junction geometry limits the device performance. A semiconductor heterojunction using ZnO as an electron acceptor was built and the device efficiency increased to 3%. By studying the light absorption and charge extraction profile of the bilayer device, the absorber layer has a charge extraction dead zone which is beyond the reach of the built-in electric field. Therefore, strategies to create a QD bulk heterojunction were considered to address this issue by distributing the junction interface throughout the absorber layer. However, the charge separation mechanism of the QD heterojunction is not clearly understood: whether it operates as an excitonic or a depleted p-n junction, as the junction operating mechanism determines the scale of phase separation in the bulk morphology. This study shows a transitional behaviour of the PbS/ZnO heterojunction from excitonic to depletion by increasing the doping density of ZnO. To utilise the excitonic mechanism, a PbS/ZnO nanocrystal bulk heterojunction was created by blending the two nanocrystals in solution such that a large interface between the two materials could facilitate fast exciton dissociation. However, the devices show poor performance due to a coarse morphology and formation of germinate pairs. To create a bulk heterojunction where a built-in electric field could assist the charge separation, a TiO2 porous structure with the pore size matching with the depletion width was fabricated and successfully in-filled by PbS QDs. The porous device produces 5.7% power conversion efficiency, among one of the highest in literature. The enhancement comes from increased light absorption and suppression of charge recombination.
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Malins, David B. "Ultrafast dynamics in InAs quantum dot and GaInNAs quantum well semiconductor heterostructures." Thesis, University of St Andrews, 2008. http://hdl.handle.net/10023/404.
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The quantum confined Stark effect (QCSE) and ultrafast absorption dynamics near the bandedge have been investigated in p-i-n waveguides comprising quantum confined heterostructures grown on GaAs substrates, for emission at 1.3um. The materials are; isolated InAs/InGaAs dot-in-a-well (DWELL) quantum dots (QD), bilayer InAs quantum dots and GaInNAs multiple quantum wells (MQW). The focus was to investigate these dynamics in a planar waveguide geometry, for the purpose of large scale integration in optical systems. Initial measurements of the QCSE using photocurrent measurements showed a small shift for isolated QDs whilst a significant shift of 40nm (at 1340nm) was demonstrated for bilayer dots, comparable to that of GaInNAs MWQ (30nm at 1300nm). These are comparable to InP based quaternary multiple quantum wells used in modulator devices. With the use of a broadband continuum source the isolated quantum dots exhibit both a small QCSE (15nm at 1280nm) and minimal broadening which is desirable for saturable absorbers used in monolithic modelocked semiconductor lasers (MMSL). A robust experimental set-up was developed for characterising waveguide modulators whilst the electroabsorption and electro-refraction was calculated (dn=1.5x10⠻³) using the Kramers-Kronig dispersion relation. Pump probe measurements were performed at room temperature using 250fs pulses from an optical parametric oscillator (OPO) on the three waveguide samples. For the isolated QDs ultrafast absorption recovery was recorded from 62ps (0V) to 700fs (-10V and the shortest times shown to be due to tunneling. Additionally we have shown good agreement of the temperature dependence of these dots and the pulse width durations from a modelocked semiconductor laser using the same material. Bilayer QDs are shown to exhibit ultrafast absorption recovery from 119ps (0V) to 5ps (-10V) offering potential for applications as modelocking elements. The GaInNAs multiple quantum wells show absorption recovery of 55ps (0V), however under applied reverse bias they exhibit long lived field screening transients. These results are explained qualitatively by the spatial separation of electrons and holes at heterobarrier interfaces.
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Leyman, Ross. "Quantum dot-based semiconductor Terahertz transceiver systems." Thesis, University of Dundee, 2014. https://discovery.dundee.ac.uk/en/studentTheses/be4e84c1-7914-4911-bd10-5fcd4bc93551.
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Terahertz (THz) technology is still currently a rapidly developing area of research with applications already demonstrated in the fields of biology, medicine, security, chemical/materials inspection and astrophysics to name a few. The diversity of applications which require the generation and measurement of THz or sub-millimeter (sub-mm) electromagnetic (EM) signals is the result of the vast number of chemical elements and compounds which exhibit molecular transitions and vibrational behavior that occur at frequency ranges corresponding to the so-called 'THz gap', roughly defined as 0.05-10 THz. The THz gap was named as such because of the relative difficulty in generating and analysing EM waves in this frequency band. This was due to the inherent challenges in generating either electrical signals with response periods below 1 picosecond (ps), or optical signals with wavelengths in the far-infrared (FIR) range. High absorption of THz signals in atmosphere via absorption by molecules such as H2O also impeded early developments and is a key issue in THz systems even today. There is now a wide variety of THz system solutions, each of which exhibits a different set of operational advantages and limitations. Arguably, the most well-established THz technique to date is based on the use of photoconductive antennas (PCAs) driven by ultrafast pulsed or dual-wavelength laser systems. This technique is the basis for the work presented in this thesis, which is an investigation into the potential utilisation of quantum dot (QD)-based semiconductor materials and devices in THz systems. This thesis discusses the work carried out in the development of a novel class of PCA devices which were postulated to enable efficient optical-to-THz signal conversion, whilst also overcoming several major limitations normally exhibited by PCA devices such as limited optical wavelength pumping range and thermal breakdown. To summarise briefly, these issues were addressed by considering: the additional pump absorption energy ranges enabled by the inclusion of multiple bandgap-engineered semiconductor materials and quantum-confined structures; the higher thermal conductivity and hence pump tolerance exhibited by relatively high-quality (low defect) absorption layers; and by simultaneously harnessing the ultrafast charge carrier modulation exhibited by the integrated QDs. Additionally, some work was carried out using QD-based lasers as pump sources, with the initial intention to explore the feasibility of a fully QD-based THz transceiver system and draw some conclusions as to the future potential for ultra-compact or even lab-on-chip THz systems, for example.
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Norberg, Nicholas S. "Magnetic nanocrystals : synthesis and properties of diluted magnetic semiconductor quantum dots /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/8625.
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Dufåker, Daniel, L. O. Mereni, Fredrik K. Karlsson, V. Dimastrodonato, G. Juska, Per-Olof Holtz, and E. Pelucchi. "Exciton-phonon coupling in single quantum dots with different barriers." Linköpings universitet, Halvledarmaterial, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-67198.
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The coupling between longitudinal-optical (LO) phonons and neutral excitons in two different kinds of InGaAs pyramidal quantum dots embedded in either AlGaAs or GaAs barriers is experimentally examined. We find a slightly weaker exciton-LO-phonon coupling and increased linewidth of the phonon replicas for the quantum dots with GaAs barriers compared to the ones with AlGaAs barriers. These results, combined with the fact that the LO-phonon energy of the exciton is the same for both kinds of dots, are taken as evidence that the excitons mainly couple to LO-phonons within the QDs.Original Publication:Daniel Dufåker, L. O. Mereni, Fredrik K. Karlsson, V. Dimastrodonato, G. Juska, Per-Olof Holtz and E. Pelucchi, Exciton-phonon coupling in single quantum dots with different barriers, 2011, Applied Physics Letters, (98), 25, 251911.http://dx.doi.org/10.1063/1.3600781Copyright: American Institute of Physicshttp://www.aip.org/
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Wen, Xiaoming. "Ultrafast spectroscopy of semiconductor nanostructures." Australasian Digital Thesis Program, 2007. http://adt.lib.swin.edu.au/public/adt-VSWT20070426.110438/index.html.
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Thesis (PhD) - Swinburne University of Technology, Centre for Atom Optics and Ultrafast Spectroscopy, 2007.Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy, Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, 2007. Typescript. Bibliography: p. 122-144.
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VanSant, Kaitlyn. "Thin Film Solar Cells Using ZnO Nanowires, Organic Semiconductors and Quantum Dots." PDXScholar, 2007. https://pdxscholar.library.pdx.edu/open_access_etds/2696.
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A thin film organic/ inorganic hybrid solar cell was fabricated by incorporating ZnO nanowires, n- and p-type organic semiconductors and inorganic quantum dots. The basic cell design involved the electrodeposition of ZnO nanowires grown on a substrate coated with a transparent conductive oxide. The ZnO nanowires were coated with a thin layer of an organic n-type material, followed by a deposition of inorganic quantum dots. A p-type polymer layer was subsequently deposited and the sample was then contacted with gold to form a quantum dot layer sandwiched between a p-n junction of organic conductive materials.
Various materials and processing methods were adjusted, using I-V characteristics, photovoltage and/ or photocurrent measurements to determine the performance of the cell. Each constituent material in the basic device design was evaluated in terms of its contribution to the sample characteristics. A variety of deposition techniques were investigated to obtain homogeneous layers. Different annealing procedures were explored with the intent of balancing the time and temperatures required for electrical activation with material constraints such as tendency towards oxidation and low melting points. The effect of time on the sample characteristics was also observed. The evaluation primarily includes data for samples that led to design modifications aimed at improving both electrical properties and quantum efficiencies.
This research led to the development of a hybrid solar cell sensitized by the addition of quantum dots. The organic semiconductors were used to form a p-n junction, and the p-type polymer also served as an active absorber layer. The quantum dots were used as the inorganic absorber fayer, and the results show that the range of optical absorption in the cell can be modified by adjusting particle size. In addition, the ZnO nanowires appear to improve charge transfer, when used with materials that have favorable band offsets.
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Sabathil, Matthias. "Opto-electronic and quantum transport properties of semiconductor nanostructures /." Garching : Verein zur Förderung des Walter Schottky Instituts der Technischen Universität München, 2005. http://www.loc.gov/catdir/toc/fy1002/2008380872.html.
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Liu, William K. "Electron spin dynamics in quantum dots, and the roles of charge transfer excited states in diluted magnetic semiconductors /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8588.
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Rueda-Fonseca, Pamela. "Magnetic quantum dots in II-VI semiconductor nanowires." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENY015/document.
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Dans ce travail de thèse a été développé et étudié un nouveau type d'objet semiconducteur magnétique : des boîtes quantiques de CdMnTe insérées dans des nanofils de ZnTe/ZnMgTe constituant une structure de type cœur-coquille. L'objectif était d'étudier la croissance par épitaxie par jets moléculaires et les propriétés fondamentales de ces hétéro-structures complexes. Dans ce but deux aspects principaux ont été abordés : i) la qualité et le contrôle des propriétés structurales, électroniques et magnétiques de ces objets, grâce à une maîtrise de leur croissance et ii) l'obtention d'informations quantitatives locales sur la composition chimique de ces nanostructures inhomogènes. Pour atteindre ces objectifs, nous avons divisé notre étude en quatre étapes. La première étape de ce travail a été concentrée sur l'étude quantitative de la formation des particules d'or servant de catalyseurs à la croissance des nanofils. La seconde étape a porté sur l'analyse des mécanismes de croissance et des paramètres gouvernant la croissance des fils de ZnTe. En particulier deux types de fils ont été observés : des fils cylindriques de structure wurtzite et des fils coniques de structures zinc-blende. Un modèle de croissance guidée par la diffusion a été utilisé pour rendre compte de certains des résultats quantitatifs présentés dans cette partie. La troisième étape a concerné l'insertion de boîtes quantiques de CdMnTe dans des nanofils de structure cœur-coquille ZnTe/ZnMgTe. Une étude préalable des paramètres pertinents influençant les propriétés magnéto-optiques de ces objets, tels que le confinement de la boîte quantique, l'incorporation du Mn et l'anisotropie de contrainte créée par la structure, a été menée. La quatrième et dernière étape de ce travail a porté sur l'interprétation quantitative de mesures d'analyse dispersive en énergie effectuées sur des nanofils de structure cœur-multicoquille. Un modèle géométrique a été proposé, permettant de retrouver la forme, les dimensions et la composition chimique des boîtes quantiques et des coquilles. Cette étude a été couplée à des mesures de caractérisation telles que la cathodo-luminescence, la micro-photo-luminescence et la spectroscopie magnéto-optique effectuées sur le même nanofilIn this PhD work a novel type of magnetic semiconductor object has been developed: Cd(Mn)Te quantum dots embedded in ZnTe/ZnMgTe core-shell nanowires. The goal was to investigate the growth, by molecular beam epitaxy, and the fundamental properties of these complex heterostructures. For that purpose, two main issues were addressed: i) gaining control of the structural, electronic and magnetic properties of these quantum objects by mastering their growth; and ii) obtaining quantitative local knowledge on the chemical composition of those non-homogeneous nanostructures. To tackle these topics, our research was divided into four stages. The first stage was devoted to perform a quantitative study of the formation process of the Au particles that catalyze the growth of nanowires. The second stage involved the analysis of the mechanisms and parameters governing the growth of ZnTe nanowires. In particular, two different types of nanowires were found: cone-shaped nanowires with the zinc-blende crystal structure and cylinder-shaped nanowires with the hexagonal wurtzite structure. A diffusion-driven growth model is employed to fit some of the quantitative results presented in this part. The third stage focused on the insertion of pure CdTe quantum dots containing Mn ions in the core-shell nanowires. An initial study of the relevant parameters influencing the magneto-optical properties of these objects, such as the quantum dot confinement, the Mn incorporation, and the strain anisotropy, was performed. The four and last stage of this work concerned the quantitative interpretation of Energy-Dispersive X-ray spectroscopy measurements performed on single core-multishell nanowires. A geometrical model was proposed to retrieve the shape, the size and the local composition of the quantum dot insertions and of the multiple layers of the heterostructures. This study was coupled to other complementary characterization measurements on the same nanowire, such as cathodo-luminescence, micro-photo-luminescence and magneto-optical spectroscopy
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Moreira, Wendel Lopes. "Síntese e estabilização de pontos quânticos coloidais de semicondutores II-VI e IV-VI." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277440.
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Orientador: Carlos Lenz CesarDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica
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Wen, Yuan, and 文苑. "Theoretical and experimental studies of electronic states in InAs/GaAsself-assembled quantum dots." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43224003.
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Perez, Barraza Julia Isabel. "Ultrasmall silicon quantum dots for the realization of a spin qubit." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708003.
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Elouneg-Jamroz, Miryam. "Croissance catalysée de nanofils de ZnSe avec boîtes quantiques de CdSe." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY049/document.
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Des nanofils de ZnSe catalysés avec de l'or ont été synthétisés pour la première fois sur pseudo-substrats de ZnSe déposé sur GaAs. La nucléation de l'or a été étuidiée en détails. Des nanoparticules d'or de diamètres homogènes ont été produites. Ces nanoparticules conduisent à la création de nanofils de diamètres de l'ordre des diamètres de Bohr des excitons dans le ZnSe et dans le CdSe. Les très basses densités de nanoparticules d'or obtenues permettent la croissance de nanofils de ZnSe dans un mode non-compétitif. La croissance a été étudiée en fonction de la variation de certains paramètres. Un rapport de flux élevé de Se:Zn~4, ainsi qu'une température aux alentours des 400C donnent lieu aux nanofils les plus droits. Les nanofils résultant de ces conditions sur ZnSe (001) s'orientent selon deux axes. La vitesse de croissance des nanofils peut être modélisée par la diffusion d'adatoms vers l'interface de croissance du nanofil. Il est démontré à l'aide d'observations RHEED que la croissance se déroule dans un mode vapeur-solide-solide (VSS), c'est à dire, avec un catalyseur à l'état solide. Une croissance dans le mode ALE produit des nanofils orientés selon un seul axe. L'incorporation de BQ de CdSe à été étudiée en détails par le biais de plusieurs techniques expérimentales. Il est possible d'obtenir des BQ de CdZnSe de quelques nanomètres de long, avec des hétérojonctions abruptes et contenant aux alentours de 50% de Cd. L'étude optique de ces BQ montre de fines raies excitoniques. L'émission de photons uniques a été mesurée sur la raie biexcitonique jusqu'à la température ambiante. À cause de la présence d'une émission discrète du substrat des nanofils, ceux-ci doivent être transférés sur un substrat non-luminescent pour les études optiquesGrowth of Au-catalysed ZnSe NWs has been successfully achieved on ZnSe peudo-substrates grown on GaAs substrate for the 1st time. Nucleation of the gold catalyst nanoparticles was studied in details. Au nanoparticles with homogeneous diameters are achieved. The nanowire diameter that results from these nanoparticles is in the range of the Bohr diameter of excitons in ZnSe and CdSe. Ultralow density achieved for Au nanoparticles makes it possible to grow nanowires in a non-competitive mode. Study of the influence of the growth parameters was done in details. A high Se:Zn~4 flux ratio and a growth temperature in the low 400C range are found to yield the straightest NWs. Homogeneous NWs with two main orientations are obtained on (001) ZnSe. The nanowire growth rate can be modeled by a kinetic mass-transport model of impinging adatoms flowing to the nanowire growth front. ZnSe NW growth was identified as taking place in the VSS mode, that is, with a solid catalyst, by in-situ RHEED observations. A growth of NWs by ALE yields only a single NW orientation. Incorporation of CdSe QDs was studied in details with numerous experimental techniques. It is possible to obtain CdZnSe QDs with a length of a few nanometers with compositionally sharp heterojunctions and a composition in Cd of about 50%. The optical study of such NWs shows sharp excitonic lines. Single photon emission on the biexciton was measured up to room temperature. A limitation comes from the fact that the NWs must be detached from the surface to be studied due to the presence of a discreet background emission originating from the substrate
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Wen, Yuan. "Theoretical and experimental studies of electronic states in InAs/GaAs self-assembled quantum dots." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43224003.
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Koroknay, Elisabeth [Verfasser]. "Epitaxial processes for low-density quantum dots in III/V semiconductors / Elisabeth Koroknay." München : Verlag Dr. Hut, 2014. http://d-nb.info/1051549795/34.
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Kanuchok, Jonathan L. "The thermal effect and clocking in quantum-dot cellular automata." Virtual Press, 2004. http://liblink.bsu.edu/uhtbin/catkey/1286605.
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We present a theoretical study of quasi-adiabatic clocking and thermal effect in Quantum-dot Cellular Automata (QCA). Quasi-adiabatic clocking is the modulation of an inter-dot potential barrier in order to keep the QCA cells near the ground state throughout the switching process. A time-dependent electric field is calculated for arrays of charged rods. The electron tunneling between dots is controlled by raising and lowering a potential barrier in the cell.A quantum statistical model has been introduced to obtain the thermal average of polarization of a QCA cell. We have studied the thermal effect on QCA devices. The theoretical analysis has been approximated for a two-state model where the cells are in one of two possible eigenstates of the cell Hamiltonian. In general, the average polarization of each cell decreases with temperature and the distance from the driver cells. The results demonstrate the critical nature of temperature dependence for the operation of QCA.Department of Physics and Astronomy
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Gehl, Michael R. "Controlling Light-Matter Interaction in Semiconductors with Hybrid Nano-Structures." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/581325.
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Nano-structures, such as photonic crystal cavities and metallic antennas, allow one to focus and store optical energy into very small volumes, greatly increasing light-matter interactions. These structures produce resonances which are typically characterized by how well they confine energy both temporally (quality factor–Q) and spatially (mode volume–V). In order to observe non-linear effects, modified spontaneous emission (e.g. Purcell enhancement), or quantum effects (e.g. vacuum Rabi splitting), one needs to maximize the ratio of Q/V while also maximizing the coupling between the resonance and the active medium. In this dissertation I will discuss several projects related by the goal of controlling light-matter interactions using such nano-structures. In the first portion of this dissertation I will discuss the deterministic placement of self-assembled InAs quantum dots, which would allow one to precisely position an optically-active material, for maximum interaction, inside of a photonic crystal cavity. Additionally, I will discuss the use of atomic layer deposition to tune and improve both the resonance wavelength and quality factor of silicon based photonic crystal cavities. Moving from dielectric materials to metals allows one to achieve mode-volumes well below the diffraction limit. The quality factor of these resonators is severely limited by Ohmic loss in the metal; however, the small mode-volume still allows for greatly enhanced light-matter interaction. In the second portion of this dissertation I will investigate the coupling between an array of metallic resonators (antennas) and a nearby semiconductor quantum well. Using time-resolved pump-probe measurements I study the properties of the coupled system and compare the results to a model which allows one to quantitatively compare various antenna geometries.
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Veloso, Aline Bessa. "Propriedades ópticas de pontos quânticos empilhados de InP/GaAs." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277760.
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Orientador: Fernando IikawaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Nesta dissertação, estudamos as propriedades ópticas e estruturais de pontos quânticos (QDs) empilhados de InP/GaAs, crescidos por método de auto-formação, conhecido como o modo Stranskii-Krastanov, em um sistema de epitaxia por feixe químico. Os pontos quânticos de InP/GaAs possuem alinhamento das bandas tipo-II nas interfaces, onde somente o elétron fica confinado no QD, enquanto o buraco fica localizado em volta dele na camada de GaAs atraído pelo elétron. Investigamos amostras com diferentes separação d entre duas camadas de QDs de InP, variando de 3 a 12 nm. As análises estruturais foram feitas por técnica microscopia eletrônica de transmissão (TEM) e as análises ópticas por fotoluminescência de feixe contínuo (PL-CW) e de resolvida no tempo (PL-RT) com a temperatura variando de 2 a 120 K. As imagens de TEM mostram alinhamento vertical dos QDs e maiores tamanhos para os que estão na segunda camada. As medidas de PL-CW, a baixas temperaturas, apresentam largura de linha da banda de emissão mais estreita e simétrica nas amostras de QDs empilhados do que a de amostra de uma camada simples. Isso é atribuído à maior uniformidade de tamanhos de QDs da segunda camada. Atribuímos aos efeitos de acoplamento quântico e de tunelamento dos portadores entre QDs, à redução de energia do pico de PL com a diminuição de d. Observamos que o decaimento temporal de PL é independente de d e é relativamente rápido, ~0,6 ns, para uma estrutura com alinhamento de banda tipo-II. Isso sugere a presença de outros canais de captura de portadores de cargas reduzindo o tempo de vida dos éxcitons em nossos QDs. Observamos também uma redução do tempo de vida na região de maior energia de emissão em todas as amostras, indicando a transferência de portadores de cargas dos QDs muito pequenos para os grandes. O aumento da temperatura resultou na redução da energia de transição e da intensidade integrada nas medidas de PL-CW, bem como, do tempo de vida dos éxcitons. A redução da energia de transição se deve à transferência de elétrons dos QDs pequenos para grandes via wetting layer, devido à excitação térmica. Mas a contribuição desse efeito é menor nas amostras de QDs empilhados, devido aos efeitos de tunelamento dos elétrons entre QDs alinhados e à uniformidade dos tamanhos. A redução da intensidade integrada de PL e no tempo de decaimento se deve a excitação térmica do elétron para o estado contínuo da wetting layer
Abstract: We studied the optical and structural properties of stacked InP/GaAs quantum dots (QD) grown by the self-organized Stranskii-Krastanov mode in a chemical beam epitaxy system. The InP/GaAs quantum dots present type-II band alignment, where only the electron is confined in the QD, while the hole is localized around it, in the GaAs layer, due to the Coulomb attraction. We investigated samples with different space-layer d between two stacked InP QDs varying from 3 to 12 nm. The structural analysis was performed by using transmission electronic microscopy (TEM) and the optical analysis by using continuous wave (CW) and time-resolved (TR) photoluminescence (PL) techniques with temperature varying from 2 to 120 K. The TEM images show clear vertical alignment of quantum dots and slightly larger size for QDs of the second layer. The CW-PL spectra measured at low temperatures present narrower QD emission band and more symmetric for stacked QDs samples than single layer one. This is attributed to the uniformity of the QDs in double layers samples. We also observed the PL red-shift with the reduction of d, which is attributed to the quantum coupling and the tunneling effects of the carriers between aligned QDs. We observed that the PL decay time is independent of d and is relatively fast, ~0,6 ns, for a structure with type-II band alignment. This suggests the presence of other carrier capture channels that reduce significantly the exciton lifetime in our QDs. The carrier lifetime is shorter in the higher emission energy region in all samples, indicating the carrier transference from the smaller QDs to the larger ones. Increasing the temperature we observed a reduction of the transition energy and the integrated CW-PL intensity, as well as, of the exciton lifetime. The energy shift is due to the electron transference from the small QDs to the larger ones, through wetting layer, due to the thermal excitation. The contribution of this effect is smaller on the stacked QDs, due to the dot uniformity and the electron tunneling effect. The reduction of the CW-PL integrated intensity and the carrier decay time is due to the thermal excitation of the electron to the continuous state of the wetting layer
Mestrado
Física da Matéria Condensada
Mestre em Física
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Santos, Graciely Elias dos 1986. "Acoplamento em estruturas híbridas : poço e pontos quânticos." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276971.
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Orientador: Maria José Santos Pompeu BrasilDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Neste trabalho estudamos o efeito de acoplamento eletrônico entre duas estruturas quânticas com uma separação variável entre elas. Utilizamos como base para este estudo um poço quântico de GaAs/ AlGaAs e pontos quânticos de GaSb/ AlGaAs. Uma característica particular desta estrutura é que os pontos quânticos GaSb/ AlGaAs apresentam interfaces do tipo-li, onde apenas os buracos ficam confinados nos pontos de GaSb, enquanto os elétrons permanecem na barreira de AlGaAs próximos ao pontos quânticos devido a atração Coulombiana. De maneira geral, um poço de GaAs com barreiras de AlGaAs possui interface do tipo-I, confinando ambos os portadores, elétrons e buracos. No entanto, escolhendo uma espessura apropriada para o poço, é possível projet ar uma estrutura onde os portadores fiquem confinados em camadas distintas: elétrons no poço de GaAs e buracos nos pontos de GaSb. Nosso trabalho se baseia em estruturas deste tipo, incluindo amostras com separações diferentes entres o poço e os pontos quânticos. Estas amostras serviram de base para estudarmos o acoplamento entre as funções de onda dos portadores separados espacialmente. As amostras estudadas foram crescidas por Epitaxia de Feixe Molecular (MBE) com diferentes espessuras da camada de separação (10, 5 e 2 nm) entre o poço e os pontos, incluindo uma amostra de referência que contém apenas um plano de pontos quânticos. Realizamos um estudo sistemático das propriedades ópticas destas estruturas através de medidas de fotoluminescência, analisando parâmetros como a temperatura da amostra, a potência e a energia da excitação, além de medidas com resolução temporal. Nossos resultados mostraram que a espessura da camada de separação é um parâmetro crucial que afeta criticamente o overlap entre as funções de onda e o tempo de vida dos portadores na amostra. Este tipo de controle pode ser interessante para estudar questões de física fundamental e para projetar dispositivos onde seja necessário controlar parâmetros como a eficiência óptica e o tempo de vida dos portadores
Abstract: In this work we studied the electronic coupling between two quantum structures with a varying space-layer between them. The base for this study is a GaAs/ AlGaAs QW and GaSb/ AlGaAs QDs. One particular feature of this structure is that the QD system exhibits a type-II interface where only holes are confined in the GaSb dot , whereas the electrons remain in the AlGaAs barrier surrounding the dot due to their Coulombic attraction. The GaAs/ AlGaAs QW exhibits type-I interface, confining both carriers, electrons and holes. However, by choosing an appropriate thickness for the QW it is possible to design a structure in order to localize both carriers in different structures: electrons on GaAs QW and holes in GaSb QDs. These samples are the base to study the carrier wavefunctions when they are spatially separated. Samples were grown by Molecular Beam Epitaxy with different space-layer thicknesses (10, 5 and 2 nm) separating the GaSb dot layer and the GaAs well, including a reference sample consisting solely of a GaSb dot layer. We studied systematically the optical properties of this system performing photoluminescence measurements, by changing parameters as sample temperature, power and energy excitation as well time resolved measurements. Our results shown that the space layer thickness is a crucial parameter that strongly affects the spatial localization of the carriers in our structure. It can, therefore, be used to control the optical properties of the structure, such as carrier wavefunction overlap and radiative recombination time. The results show this overlap control may be interesting for fundamental physics studies and to design devices where controlling optical efficiency and carrier lifetimes are essential
Mestrado
Física
Mestra em Física
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Matas, Adams Alba Maria. "Semiconductor Nanoparticles as Platform for Bio-Applications and Energy Related Systems." Doctoral thesis, Universitat Rovira i Virgili, 2015. http://hdl.handle.net/10803/334391.
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Aquesta tesi està dedicada a la síntesi, caracterització i aplicacions de diferents nanomaterials que presenten la propietat de ser semiconductors.
Aquesta dividida en tres blocs, en els quals, en el primer d'ells es parla sobre quantum dots (QDs), que són nanoparticulas fluorescents la longitud d'ona d'emissió varia amb la mida. Aquests materials s'estan utilitzant últimament com a substituts dels colorants orgànics ja que presenten avantatges, la principal és que no perden la seva emissió amb el temps.
Aquests QDs han estat usats per estudiar la seva interacció amb l'or (que augmenta la seva intensitat de fluorescència), han estat encapsulats usant polímers per usar-los com a controls en citometria de flux i per silica per usar-los (un cop units a un peptido i un colorant orgànic adequat) com a detectors de fibrosi quística. Finalment també han estat usats en aquesta tesi per intentar seguir el moviment d'un receptor en plaquetes.
En el segon bloc de la tesi es parla de up conversió nanoparticles, la diferència enfront dels QDs és que s'exciten a major longitud d'ona a la que emeten, pel que són capaços d'absorbir en el infraroig i emetre en el visible, fent-ideals per a aplicacions en biologia. En aquesta tesi es van usar per a reconèixer un receptor en neutrofilos i per introduir-lo dins de hidrotalcites (material que no és reconegut pel cos com estrany) per així poder alliberar-ho en l'organisme.
Finalment, en el tercer bloc s'han sintetitzat materials per catalisis (sulfur de bismut) i per cel·les solars (òxid de titani)Esta tesis esta dedicada a la sintesis, caracterizacion y aplicaciones de diferentes nanomateriales que presentan la propiedad de ser semiconductores. Esta dividida en tres bloques, en los cuales, en el primer de ellos se habla sobre quantum dots (QDs), que son nanoparticulas fluorescentes cuya longitud de onda de emision varia con el tamaño. Dichos materiales se estan usando ultimamente como sustitutos de los colorantes organicos ya que presentan ventajas, la principal es que no pierden su emision con el tiempo. Estos QDs han sido usados para estudiar su interaccion con el oro (que aumenta su intensidad de fluorescencia), han sido encapsulados usando polimeros para usarlos como controles en citometria de flujo y por silica para usarlos (una vez unidos a un peptido y un colorante organico adecuado) como detectores de fibrosis quistica. Finalmente tambien han sido usados en esta tesis para intentar seguir el movimiento de un receptor en plaquetas. En el segundo bloque de la tesis se habla de up conversion nanoparticles, cuya diferencia frente a los QDs es que se excitan a mayor longitud de onda a la que emiten, por lo que son capaces de absorber en el infrarojo y emitir en el visible, haciendolos ideales para aplicaciones en biologia. En esta tesis se usaron para reconocer un receptor en neutrofilos y para introducirlo dentro de hidrotalcitas (material que no es reconocido por el cuerpo como extraño) para asi poder liberarlo en el organismo. Finalmente, en el tercer bloque se han sintetizado materiales para catalisis (sulfuro de bismuto) y para celdas solares (oxido de titanio).
This thesis is dedicated to the synthesis, characterization and application of different nanomaterials that are semiconductors. It is divided in three blocks, in the first one we talk about quantum dots (QDs), that are fluorescent nanoparticles whose wavelength of emission changes with size. Such materials are being used as substitutes of organic dyes, due to the many advantages they present, the main one is that the fluorescence is not lost with time. These QDs have been used to study their interaction with gold ( that increases the fluorescence intensity), they have been encapsulated with polimers to be used as controls in flow cytometry or by silica to use them as sensors for cystic fibrosis (once they have been attatched to the right polymer and dye). Finally, in this thesis, they have been also used to track the movement of a platelet receptor. In the second block we talk about up conversion nanoparticles, which only difference regarding QDs is that they are excited using a longer wavelength than the emission, so they are able to absorb in the infrared and emit in the visible range of light, making them ideal for biological applications. We have use this materials to recognice an specific receptor in neutrophils as well as to be surrounded by hydrotalcite (body friendly material) so it can be released in the organism. Finally, in the third block we have syntesized materials for catalysis (bismuth sulfide) and for solar cells (titanium oxide for perovskite solar cells).
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Palacios-Berraquero, Carmen. "Quantum-confined excitons in 2-dimensional materials." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275721.
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The 2-dimensional semiconductor family of materials called transition metal dichalcogenides (2d-TMDs) offers many technological advantages: low power consumption, atomically-precise interfaces, lack of nuclear spins and ease of functional integration with other 2d materials are just a few. In this work we harness the potential of these materials as a platform for quantum devices: develop a method by which we can deterministically create single-photon emitting sites in 2d-TMDs, in large-scale arrays. These we call quantum dots (QDs): quantum confinement potentials within semiconductor materials which can trap single-excitons. The single excitons recombine radiatively to emit single-photons. Single-photon sources are a crucial requirement for many quantum information technology (QIT) applications such as quantum cryptography and quantum communication. The QDs are formed by placing the flakes over substrates nano-patterned with protru- sions which induce local strain and provoke the quantum confinement of excitons at low temperatures. This method has been successfully tested in several TMD materials, hence achieving quantum light at different wavelengths. We present one of the very few systems where quantum confinement sites have been shown to be deterministically engineered in a scalable way. Moreover, we have demonstrated how the 2d-based QDs can be embedded within 2d- heterostructures to form functional quantum devices: we have used TMD monolayers along with other 2d-materials - graphene and hexagonal boron nitride - to create quan- tum light-emitting diodes that produce electrically-driven single-photons. Again, very few single-photon sources can be triggered electrically, and this provides a great ad- vantage when considering on-chip quantum technologies. Finally, we present experimental steps towards using our architecture as quantum bits: capturing single-spins inside the QDs, using field-effect type 2d-heterostructures. We are able to controllably charge the QDs with single-electrons and single-holes – a key breakthrough towards the use of spin and valley pseudospin of confined carriers in 2d-materials as a new kind of optically addressable matter qubit. This work presents the successful marriage of 2d-semiconductor technology with QIT, paving the way for 2-dimensional materials as platforms for scalable, on-chip quantum photonics.
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Nemitz, Ian R. "Synthesis of Nanoscale Semiconductor Heterostructures for Photovoltaic Applications." Bowling Green State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1277087935.
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Royo, Romero Luis. "Optoelectronic Characteristics of Inorganic Nanocrystals and Their Solids." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1555422820907262.
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Olofsson, Karl-Johan. "Black-box optimization of simulated light extraction efficiency from quantum dots in pyramidal gallium nitride structures." Thesis, Linköpings universitet, Matematiska institutionen, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-162235.
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Microsized hexagonal gallium nitride pyramids show promise as next generation Light Emitting Diodes (LEDs) due to certain quantum properties within the pyramids. One metric for evaluating the efficiency of a LED device is by studying its Light Extraction Efficiency (LEE). To calculate the LEE for different pyramid designs, simulations can be performed using the FDTD method. Maximizing the LEE is treated as a black-box optimization problem with an interpolation method that utilizes radial basis functions. A simple heuristic is implemented and tested for various pyramid parameters. The LEE is shown to be highly dependent on the pyramid size, the source position and the polarization. Under certain circumstances, a LEE over 17% is found above the pyramid. The results are however in some situations very sensitive to the simulation parameters, leading to results not converging properly. Establishing convergence for all simulation evaluations must be done with further care. The results imply a high LEE for the pyramids is possible, which motivates the need for further research.
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Mendes, Udson Cabral 1984. "Electronic and optical properties of diluted magnetic semiconductors quantum wells and quantum dots = Propriedades eletrônicas e ópticas de poços quânticos e pontos quânticos de semicondutores magnéticos diluídos." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/276958.
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Orientador: José Antônio BrumTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Nesta tese, investigamos teoricamente as propriedades eletrônicas e ópticas de poços quânticos e pontos quânticos de semicondutores magnéticos diluídos. Este estudo é fortemente motivado por muitos resultados experimentais sobre as propriedades ópticas desse materiais. Usando a teoria do funcional da densidade dependente de spin descrevemos os estados eletrônicos como função do campo magnético externo para poços quânticos que possuem barreiras dopadas com impurezas magnéticas. Nosso modelo leva em conta os efeitos de muitos-corpos do gás de buracos e as interações entre portadores e os íons magnéticos. Comparamos nossos resultados com os dados experimentais disponíveis, que apresentam forte oscilações da luz polarizada circularmente como função do campo magnético. Nossos resultados apresentam excelente concordância qualitativa e quantitativa com os resultados experimentais. Mostramos que os efeitos de troca do gás de buraco são responsáveis pela forte oscilação observada na fotoluminescência. Também realizamos uma investigação sistemática dos parâmetros da heteroestrutura afim de aumentar a interação de troca entre portadores e íons de Mn. Com o nosso modelo entedemos os diferentes regimes de relaxação de spin do elétron em poços quânticos com barreiras dopadas com impurezas magnéticas. Nós também investigamos as propriedades eletrônicas e ópticas de pontos quânticos carregados dopados com uma única impureza magnética em seu centro. Usando métodos de diagonalização exata mostramos que os elétrons que não estão diretamente acoplados com o íon de Mn acoplam-se via uma interação indireta que é mediada pela interação elétron-elétron. Este acoplamento indireto entre elétrons e Mn pode ser tanto ferromagnético quanto antiferromagnético dependendo de ambos confinamento e número de camadas eletrônicas confinadas no ponto quântico. Demonstramos que este acoplamento indireto é um efeito importante mesmo quanto o íon de Mn não esta no centro do ponto quântico. O acoplamento indireto existe independentemente do tipo de interação direta entre portadores e a impureza magnética. Também extendemos a teoria de fotoluminescência para essa heteroestrutura. Observamos que a interação indireta entre portadores e íon magnético gera uma estrutura fina em ambos os estados iniciais e finais da emissão, o que nos permite determinar o número de camadas confinadas no ponto quântico e o spin eletrônico. Com esse método de diagonalização exata, explicamos a origem da estrutura fina do biexciton confinado em um ponto quântico dopado com uma única impureza magnética
Abstract: In this thesis, we theoretically investigate the electronic and optical properties of diluted magnetic semiconductors quantum wells and quantum dots. This is strongly motivated by many experimental results on the optical properties of these materials. Using spin-density functional theory we described the electronic states as a function of the external magnetic field for quantum wells which have barriers doped with magnetic impurities. Our model takes into account the many-body effects of the two-dimensional hole gas and the interaction between carriers and the magnetic ions. We compare our findings with the available experimental data, which shows strong oscillations in the circularly polarized light as a function of the magnetic field. Our results show excellent qualitative and quantitative agreement with the experimental data. We show that the hole gas exchange effects are responsible for the strong oscillations observed in the photoluminescence. We perform a systematic investigation of the heterostructure parameters in order to enhance the carriers-Mn exchange interaction. With our model we understand the different regime of the electron¿s spin relaxation in quantum wells with barriers doped with Mn impurities. We also investigate the electronic and optical properties of charged quantum dots doped with a single magnetic impurity in its center. Using an exact diagonalization method we show that the electrons that are not directly coupled with Mn do so via an indirect coupling mediated by electron-electron interaction. This indirect electron-Mn coupling can be either ferromagnetic or antiferromagnetic depending on both quantum dot confinement and the number of electronic confined shells. We also demonstrate that the indirect electron-Mn coupling is an important effect even when Mn is off-center. This coupling exists independently of the type of the direct interaction between carriers and Mn impurity. We also extend the theory of photoluminescence for charged quantum dots containing a single magnetic impurity. We show that the indirect interaction between carriers and magnetic ion generates a fine structure in both initial and final states of the emission, which allows us to determinate the number of confined shells in the quantum dots and the electronic spins. Whit this exact diagonalizationmethod, we explain the origin of the fine structure of a biexciton confined in quantum dot containing a single Mn impurity
Doutorado
Física
Doutor em Ciências
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Kairdolf, Brad A. "Development of polymer-coated nanoparticle imaging agents for diagnostic applications." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31845.
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Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Nie, Shuming; Committee Member: Bao, Gang; Committee Member: Murthy, Niren; Committee Member: Varma, Vijay; Committee Member: Wang, Zhong Lin. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Tallapally, Venkatesham. "Colloidal Synthesis and Photophysical Characterization of Group IV Alloy and Group IV-V Semiconductors: Ge1-xSnx and Sn-P Quantum Dots." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5568.
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Nanomaterials, typically less than 100 nm size in any direction have gained noteworthy interest from scientific community owing to their significantly different and often improved physical properties compared to their bulk counterparts. Semiconductor nanoparticles (NPs) are of great interest to study their tunable optical properties, primarily as a function of size and shape. Accordingly, there has been a lot of attention paid to synthesize discrete semiconducting nanoparticles, of where Group III-V and II-VI materials have been studied extensively. In contrast, Group IV and Group IV-V based nanocrystals as earth abundant and less-non-toxic semiconductors have not been studied thoroughly. From the class of Group IV, Ge1-xSnx alloys are prime candidates for the fabrication of Si-compatible applications in the field of electronic and photonic devices, transistors, and charge storage devices. In addition, Ge1-xSnx alloys are potentials candidates for bio-sensing applications as alternative to toxic materials. Tin phosphides, a class of Group IV-V materials with their promising applications in thermoelectric, photocatalytic, and charge storage devices. However, both aforementioned semiconductors have not been studied thoroughly for their full potential in visible (Vis) to near infrared (NIR) optoelectronic applications. In this dissertation research, we have successfully developed unique synthetic strategies to produce Ge1-xSnx alloy quantum dots (QDs) and tin phosphide (Sn3P4, SnP, and Sn4P3) nanoparticles with tunable physical properties and crystal structures for potential applications in IR technologies.
Low-cost, less-non-toxic, and abundantly-produced Ge1-xSnx alloys are an interesting class of narrow energy-gap semiconductors that received noteworthy interest in optical technologies. Admixing of α-Sn into Ge results in an indirect-to-direct bandgap crossover significantly improving light absorption and emission relative to indirect-gap Ge. However, the narrow energy-gaps reported for bulk Ge1-xSnx alloys have become a major impediment for their widespread application in optoelectronics. Herein, we report the first colloidal synthesis of Ge1-xSnx alloy quantum dots (QDs) with narrow size dispersity (3.3±0.5 – 5.9±0.8 nm), wide range of Sn compositions (0–20.6%), and composition-tunable energy-gaps and near infrared (IR) photoluminescence (PL). The structural analysis of alloy QDs indicates linear expansion of cubic Ge lattice with increasing Sn, suggesting the formation of strain-free nanoalloys. The successful incorporation of α-Sn into crystalline Ge has been confirmed by electron microscopy, which suggests the homogeneous solid solution behavior of QDs. The quantum confinement effects have resulted in energy gaps that are significantly blue-shifted from bulk Ge for Ge1-xSnx alloy QDs with composition-tunable absorption onsets (1.72–0.84 eV for x=1.5–20.6%) and PL peaks (1.62–1.31 eV for x=1.5–5.6%). Time-resolved PL (TRPL) spectroscopy revealed microsecond and nanosecond timescale decays at 15 K and 295 K, respectively owing to radiative recombination of dark and bright excitons as well as the interplay of surface traps and core electronic states. Realization of low-to-non-toxic and silicon-compatible Ge1-xSnx QDs with composition-tunable near IR PL allows the unprecedented expansion of direct-gap Group IV semiconductors to a wide range of biomedical and advanced technological studies.
Tin phosphides are a class of materials that received noteworthy interest in photocatalysis, charge storage and thermoelectric devices. Dual stable oxidation states of tin (Sn2+ and Sn4+) enable tin phosphides to exhibit different stoichiometries and crystal phases. However, the synthesis of such nanostructures with control over morphology and crystal structure has proven a challenging task. Herein, we report the first colloidal synthesis of size, shape, and phase controlled, narrowly disperse rhombohedral Sn4P3, hexagonal SnP, and amorphous tin phosphide nanoparticles (NPs) displaying tunable morphologies and size dependent physical properties. The control over NP morphology and crystal phase was achieved by tuning the nucleation/growth temperature, molar ratio of Sn/P, and incorporation of additional coordinating solvents (alkylphosphines). The absorption spectra of smaller NPs exhibit size-dependent blue shifts in energy gaps (0.88–1.38 eV) compared to the theoretical value of bulk Sn3P4 (0.83 eV), consistent with quantum confinement effects. The amorphous NPs adopt rhombohedral Sn4P3 and hexagonal SnP crystal structures at 180 and 250 °C, respectively. Structural and surface analysis indicates consistent bond energies for phosphorus across different crystal phases, whereas the rhombohedral Sn4P3 NPs demonstrate Sn oxidation states distinctive from those of the hexagonal and amorphous NPs owing to complex chemical structure. All phases exhibit N(1s) and ʋ(N-H) energies suggestive of alkylamine surface functionalization and are devoid of tetragonal Sn impurities.
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Walker, Alexandre W. "Bandgap Engineering of Multi-Junction Solar Cells for Enhanced Performance Under Concentration." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/26240.
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This doctorate thesis focuses on investigating the parameter space involved in numerically modeling the bandgap engineering of a GaInP/InGaAs/Ge lattice matched multi-junction solar cell (MJSC) using InAs/InGaAs quantum dots (QDs) in the middle sub-cell. The simulation environment – TCAD Sentaurus – solves the semiconductor equations using finite element and finite difference methods throughout well-defined meshes in the device to simulate the optoelectronic behavior first for single junction solar cells and subsequently for MJSCs with and without quantum dots under concentrated illumination of up to 1000 suns’ equivalent intensity. The MJSC device models include appropriate quantum tunneling effects arising in the tunnel junctions which serve as transparent sub-cell interconnects. These tunneling models are calibrated to measurements of AlGaAs/GaAs and AlGaAs/AlGaAs tunnel junctions reaching tunneling peak current densities above 1000 A/cm^2.
Self-assembled InAs/GaAs quantum dots (QDs) are treated as an effective medium through a description of appropriate generation and recombination processes. The former includes analytical expressions for the absorption coefficient that amalgamates the contributions from the quantum dot, the InAs wetting layer (WL) and the bulk states. The latter includes radiative and non-radiative lifetimes with carrier capture and escape considerations from the confinement potentials of the QDs. The simulated external quantum efficiency was calibrated to a commercial device from Cyrium Technologies Inc., and required 130 layers of the QD effective medium to match the contribution from the QD ground state. The current – voltage simulations under standard testing conditions (1 kW/cm^2, T=298 K) demonstrated an efficiency of 29.1%, an absolute drop of 1.5% over a control structure. Although a 5% relative increase in photocurrent was observed, a 5% relative drop in open circuit voltage and an absolute drop of 3.4% in fill factor resulted from integrating lower bandgap nanostructures with shorter minority carrier lifetimes. However, these results are considered a worst case scenario since maximum capture and minimum escape rates are assumed for the effective medium model. Decreasing the band offsets demonstrated an absolute boost in efficiency of 0.5% over a control structure, thus outlining the potential benefits of using nanostructures in bandgap engineering MJSCs.
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Kumar, Santosh. "Tuning of single semiconductor quantum dots and their host structures via strain and in situ laser processing." Doctoral thesis, Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-120799.
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Single self-assembled semiconductor quantum dots (QDs) are able to emit single-photons and entangled-photons pairs. They are therefore considered as potential candidate building blocks for quantum information processing (QIP) and communication. To exploit them fully, the ability to precisely control their optical properties is needed due to several reasons. For example, the stochastic nature of their growth ends up with only little probability of finding any two or more QDs emitting indistinguishable photons. These are required for two-photon quantum interference (partial Bell-state measurement), which lies at the heart of linear optics QIP. Also, most of the as-grown QDs do not fulfil the symmetries required for generation of entangled-photon pairs. Additionally, tuning is required to establish completely new systems, for example, 87Rb atomic-vapors based hybrid semiconductoratomic (HSA) interface or QDs with significant heavy-hole (HH)-light-hole (LH) mixings. The former paves a way towards quantum memories and the latter makes the optical control of hole spins much easier required for spin- based QIP.
This work focuses on the optical properties of a new type of QDs optimized for HSA experiments and their broadband tuning using strain. It was created by integrating the membranes, containing QDs, onto relaxor-ferroelectric actuators and was quantified with a spatial resolution of ~1 µm by combining measurements of the µ-photoluminescence of the regions surrounding the QDs and dedicated modeling. The emission of a neutral exciton confined in a QD usually consists of two fine-structure-split lines which are linearly polarized along orthogonal directions. In our QDs we tune the emission energies as large as ~23meV and the fine-structure-splitting by more than 90 µeV. For the first time, we demonstrate that strain is able to tune the angle between the polarization direction of these two lines up to 40° due to increased strain-induced HH-LH mixings up to ~55%. Compared to other quantum emitters, QDs can be easily integrated into optoelectronic devices, which enable, for example, the generation of non-classical light under electrical injection. A novel method to create sub-micrometer sized current-channels to efficiently feed charge carriers into single QDs is presented in this thesis. It is based on focused-laserbeam assisted thermal diffusion of manganese interstitial ions from the top GaMnAs layer into the underlying layer of resonant tunneling diode structures. The combination of the two methods investigated in this thesis may lead to new QDbased devices, where direct laser writing is employed to preselect QDs by creating localized current-channels and strain is used to fine tune their optical properties to match the demanding requirements imposed by QIP concepts.
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Zallo, Eugenio. "Control of electronic and optical properties of single and double quantum dots via electroelastic fields." Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-162870.
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Semiconductor quantum dots (QDs) are fascinating systems for potential applications in quantum information processing and communication, since they can emit single photons and polarisation entangled photons pairs on demand. The asymmetry and inhomogeneity of real QDs has driven the development of a universal and fine post-growth tuning technique. In parallel, new growth methods are desired to create QDs with high emission efficiency and to control combinations of closely-spaced QDs, so-called "QD molecules" (QDMs). These systems are crucial for the realisation of a scalable information processing device after a tuning of their interaction energies.
In this work, GaAs/AlGaAs QDs with low surface densities, high optical quality and widely tuneable emission wavelength are demonstrated, by infilling nanoholes fabricated by droplet etching epitaxy with different GaAs amounts. A tuning over a spectral range exceeding 10 meV is obtained by inducing strain in the dot layer. These results allow a fine tuning of the QD emission to the rubidium absorption lines, increasing the yield of single photons that can be used as hybrid semiconductor-atomic-interface.
By embedding InGaAs/GaAs QDs into diode-like nanomembranes integrated onto piezoelectric actuators, the first device allowing the QD emission properties to be engineered by large electroelastic fields is presented. The two external fields reshape the QD electronic properties and allow the universal recovery of the QD symmetry and the generation of entangled photons, featuring the highest degree of entanglement reported to date for QD-based photon sources.
A method for controlling the lateral QDM formation over randomly distributed nanoholes, created by droplet etching epitaxy, is demonstrated by depositing a thin GaAs buffer over the nanoholes. The effect on the nanohole occupancy of the growth parameters, such as InAs amount, substrate temperature and arsenic overpressure, is investigated as well. The QD pairs show good optical quality and selective etching post-growth is used for a better characterisation of the system.
For the first time, the active tuning of the hole tunnelling rates in vertically aligned InGaAs/GaAs QDM is demonstrated, by the simultaneous application of electric and strain fields, optimising the device concept developed for the single QDs. This result is relevant for the creation and control of entangled states in optically active QDs. The modification of the electronic properties of QDMs, obtained by the combination of the two external fields, may enable controlled quantum operations.
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Laura, M. Robinson. "USING TIME-RESOLVED PHOTOLUMINESCENCE SPECTROSCOPY TO EXAMINE EXCITON DYNAMICS IN II-VI SEMICONDUCTOR NANOSTRUCTURES." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin980259259.
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Menezes, Alan Silva de. "Estudo estrutural de nanossistemas semicondudores e semicondutores implantados por difração de raios-X de n-feixes." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278200.
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Orientador: Lisandro Pavie CardosoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Neste trabalho, a difração múltipla (DM) de raios-X associada com as vantagens da radiação síncrotron configura-se como uma microssonda de alta resolução e é utilizada para obter relevantes contribuições ao estudo das propriedades estruturais de materiais semicondutores, apresentem-se eles como nanosistemas epitaxiais ou implantados com íons. O estudo e detecção de reflexões híbridas (interação camada epitaxial/substrato) coerentes (CHR) negativas nas varreduras Renninger (RS) do substrato é uma das contribuições desta tese. O mapeamento ?:f da condição de difração da reflexão secundária (113)(111) mostra que a CHR negativa que aparece é, na realidade, a interferência destrutiva entre a reflexão secundária da rede da camada e a reflexão primária do substrato. Ressalta-se aqui importância da medida detalhada da condição de difração de reflexões secundárias adequadas da DM. O uso do caso especial da DM denominado difração Bragg-superfície (BSD), cuja reflexão secundária se propaga paralelamente à superfície dos monocristais ou interfaces nas heteroestruturas, quando envolve reflexões secundárias que são sensíveis à simetria da rede cristalina, constitui outra contribuição da tese. O pico na RS para o substrato (GaAs), que representa o caso de quatro-feixes (000)(004)(022)(022) e que se separa em dois picos na RS da camada GaInP por distorção tetragonal foi utilizado como uma nova ferramenta no estudo de deformações tetragonais, mesmo para camadas epitaxiais finas. Além disso, a presença de distorções ortorrômbicas ou até mesmo monoclínicas, pode ser investigada pela medida dos dois pares de picos secundários (022)(022) e (202)(202), também presentes na mesma RS da camada ternária. Outras contribuições desta tese estão na aplicação da DM no estudo de amostras de SiO2/Si(001) implantadas com íons Fe+, que passaram pelo processo de cristalização epitaxial induzida por feixe de íons (IBIEC) e, finalmente, por tratamento térmico. Mapeamentos ?:f do pico BSD (000)(002)(111) forneceram parâmetros de rede e tensões nas direções perpendiculares e paralelas com relação à superfície, para as regiões tensionadas provocadas por formação das nanopartículas da fase ?-FeSi2 produzidas por IBIEC. Para outro conjunto de amostras semelhantes exceto pela ausência do óxido a interessante formação de nanopartículas da fase ?-FeSi2 sob a forma de placas orientadas na amostra IBIEC, que foram observadas por microscopia e confirmadas por curvas de rocking (002) na condição de DM para os picos BSD (111) e (111) e mapeamentos ?:f, provocou tensões anisotrópicas no plano da superfície da amostra IBIEC. Formas esféricas das nanopartículas também detectadas por microscopia introduzem tensões isotrópicas e a caracterização estrutural das amostras foi realizada da mesma maneira mencionada acima. Medidas dos mapeamentos do espaço recíproco (RSM) com reflexões simétricas e assimétricas foram importante para confirmar os resultados obtidos por MD das amostras implantadas, por permitir observar a variação de composição lateral e periódica existente na camada de GaInP, assim como, por confirmar o efeito da altura dos pontos quânticos de InP sobre a camada ternária, no nível de tensão provocado por eles na camada de recobrimento desses pontos, ou seja, quanto maior a altura maior o nível de tensão na camada
Abstract: In this paper, X-ray multiple diffraction (MD) associated with the advantages of synchrotron radiation appears as a high-resolution microprobe and it is used to obtain relevant contributions to the study of structural properties of semiconductor materials, as they present themselves nanosystems epitaxial or implanted with ions. The study and detection of negative hybrid reflections (interaction epitaxial layer/substrate) coherent (CHR) in substrate Renninger scans (RS) is one of the contributions of this thesis. The ?:f mapping, i.e., the scanning of the (113)(111) secondary reflection diffraction condition shows that the CHR negative that appears is, in fact, the destructive interference between the layer secondary reflection and the substrate primary reflection. It is emphasized here the importance of a detailed measurement of the diffraction condition of adequate MD secondary reflections. The use of the MD special case named Bragg-Surface Diffraction (BSD), in which the secondary reflection propagates parallel to the single crystal surface or interfaces in heterostructures, when involves secondary reflections that are sensitive to the crystalline lattice symmetry, is another relevant contribution of this thesis. The substrate (GaAs) RS peak, which stands for the (000)(004)(022)(022) four-beam case that splits into two three-beam peaks GaInP layer RS by tetragonal distortion was used as a novel tool in the study of tetragonal distortions, even for thin epitaxial layers. Moreover, the presence of orthorhombic distortion or even monoclinic one, can be investigated by measuring the two pairs of secondary peaks (022)(022)and (202)(202) also present in the same ternary layer RS. Other thesis contributions are in the application of DM to the study of SiO2/Si(001) crystals implanted with Fe+, which were submitted to Ion Beam Induced Epitaxial Crystallization process (IBIEC) and then, annealed. ?:f mappings of the (000)(002)(111) BSD peak gave rise to perpendicular and in-plane lattice parameters and strains for the stressed regions provoked by the ?-FeSi2 nanoparticles formation provided by IBIEC. For another set of similar samples except for the absence of the oxide, the interesting formation of oriented plate-like ?-FeSi2 nanoparticles, that were observed by TEM and confirmed by (002) rocking curves obtained at MD condition for the BSD (111) and (1 peaks and the ?:f mappings that provided anisotropic in-plane strains in IBIEC sample. Nanoparticles spherical-like also detected by TEM induce isotropic strains and the samples structural characterization was obtained using the same above mentioned manner. Measurements of the reciprocal space mapping (RSM) using symmetric and asymmetric reflections were important to confirm the implanted crystal results obtained by MD by allowing to observe the periodic and lateral composition variation in the GaInP layer as well as, to confirm the effect of the height of InP quantum dots grown on the ternary layer in the strain degree they cause in the ternary cap layer, it means, the greater the height the greater the level of strain in the cap layer
Doutorado
Física da Matéria Condensada
Doutor em Ciências
50
Artioli, Alberto. "Formation de polarons magnétiques dans des boîtes quantiques de (Cd,Mn)Te insérées dans des nanofils de ZnTe." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY006/document.
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Ce travail de thèse porte sur l’étude des propriétés optiques de boites quantiques anisotropes de (Cd,Mn)Te insérées dans des nanofils de ZnTe. Les boites quantiques étudiées contenant 10% de Mn sont allongées suivant l’axe du fil ce qui tend à favoriser un état fondamental à trou léger ayant une susceptibilité de spin perpendiculaire à l’axe du fil. L’objectif principal de la thèse est l’étude de la formation du Polaron Magnétique dans ces boites et la détermination de leur anisotropie magnétique.Nous avons étudié en premier les propriétés optiques de nanofils de ZnTe et de nanofils coeurs-coquilles ZnTe/(Zn,Mg)Te. Ces études nous ont amené à modéliser les contraintes élastiques dans le cœur, dans la coquille et dans des boites allongées insérées dans les nanofils. Ce modèle nous a permis d’estimer les splittings entre les niveaux de trou lourd et de trou léger dans la boite et dans le fil.Nous avons étudié ensuite des nanofils contenant des boites magnétiques et non magnétiques par spectroscopie magnéto-optique. Dans les boites magnétiques, les interactions d’exchange entre les porteurs localisés et les spins de Mn induisent un très fort décalage Zeeman de la raie excitonique (Effet Zeeman Géant). Pour extraire des paramètres quantitatifs, nous avons combiné différentes techniques expérimentales sur le même nanofil (photo et cathodoluminescence, analyse dispersive en énergie du rayonnement X). Nous avons utilisé différentes orientations du champ magnétique pour déterminer l’anisotropie du trou dans la boite. Les valeurs expérimentales sont plus petites que les valeurs théoriques ce qui suggère un mauvais confinement du trou dans la boite.Afin d’obtenir un meilleur confinement du trou, nous avons étudié des boites de (Cd,Mn)Te entourées d’une coquille de (Zn,Mg)Te. Grace au meilleur confinement du trou, nous avons réussi à observer la formation du Polaron Magnétique excitonique. Des mesures de photoluminescence résolues en temps sur des nanofils uniques nous ont permis d’extraire l’énergie et le temps de formation du Polaron Magnétique entre 5K et 50K. La raie d’émission des boites présente un effet Zeeman géant inhabituel caractéristique d’un Polaron Magnétique à trou léger. Nous avons développé un modèle théorique pour décrire la formation du Polaron Magnétique excitonique dans les boites quantiques. Ce model, basé sur l’énergie libre et valable pour des températures et des champs magnétiques arbitraires, a été utilisé pour rendre compte de l’ensemble des données expérimentales. Ce modèle a permis de déterminer les paramètres caractéristiques du polaron magnétique à trou léger (énergie, orientation and amplitude du moment magnétique, volume d’échange, anisotropie du trou)In this PhD work we study the optical properties of anisotropic (Cd,Mn)Te magnetic quantum dots inserted in ZnTe nanowires. The quantum dots containing typically 10% of Mn spins are elongated along the nanowire axis which tend to stabilize a light hole ground state with a spin susceptibility perpendicular to the nanowire axis. The main goal was to study the formation of exciton Magnetic Polarons in such quantum dots and to determine their magnetic anisotropy.We investigate first the optical properties of ZnTe and ZnTe/(Zn,Mg)Te core shell nanowires. We model the elastic strain profile in core-shell nanowires and in elongated quantum dots. From the strain profiles, we estimate the value of the light hole heavy hole splitting expected in the dot and in the nanowire.In a second step we study single nanowires containing magnetic and non magnetic quantum dots by magneto-optical spectroscopy. The exchange interactions between confined carriers and Mn spins induce a large Zeeman shift of the exciton line (Giant Zeeman Effect). To extract quantitative parameters, we combine different experimental techniques (photo and cathodoluminescence, energy dispersive X ray spectroscopy) on the same nanowire. We use also different magnetic field orientations in order to determine the hole anisotropy in the dot. The experimental values are smaller than the theoretical ones suggesting a weak confinement of the holes in the dot due to a small (Cd,Mn)Te/ZnTe valence band offset.In a third step we study nanowires containing (Cd,Mn)Te quantum dots surrounded by a (Zn,Mg)Te alloy. Thanks to the better hole confinement induced by the (Zn,Mg)Te alloy, the formation of exciton magnetic polarons can be observed. We perform time resolved photoluminescence studies on single nanowires in order to determine the energy and the formation time of magnetic polarons from 5K to 50K. The quantum dot emission line shows an unusual Zeeman shift, characteristic of a light hole magnetic polaron. We develop a theoretical model describing the formation of exciton magnetic polaron in quantum dots. We use this model, based on the free energy and valid for any temperature and magnetic field, to fit the whole set of experimental data. It allows us to determine the characteristic parameters of the light hole magnetic polarons (energy, orientation and magnitude of the magnetic moment, exchange volume, hole anisotropy)