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An Optical Study Of The Electronic Structure Of Cdse Znse And Cdte Znte Self Assembled Quantum Dots
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Book Synopsis An Optical Study of the Electronic Structure of CdSe/ZnSe and CdTe/ZnTe Self Assembled Quantum Dots by :
Download or read book An Optical Study of the Electronic Structure of CdSe/ZnSe and CdTe/ZnTe Self Assembled Quantum Dots written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the excitonic structure and optical properties of single quantum dots in three different II-VI semiconductor structure systems: as-grown CdSe/ZnSe, as-grown CdTe/ZnTe, and annealed CdTe/ZnTe self-assembled quantum dots(QD) using photoluminescence(PL), micro-PL, micro-PL obtained using a sub-wavelength aperture, and PL images obtained using a Solid Immersion Lens (SIL). These experiments are performed both at zero field and magnetic field up to 3 Tesla. While in zero field, linear polarized PL are used to find exchange splitting and QD asymmetry direction of the three QD samples, in a 3 Tesla magnetic field, circular polarized PL is used to determine the g-factor and diamagnetic shift. With a solid immersion lens (SIL), we are able to directly image a large number of single QD at 6K with 400 nm spatial resolution. Using zero field measurements, we find that while the some of the QDs are symmetric, and emit completely unpolarized light, over half of the QDs are antisymmetric which are typically aligned along one of the in-plane crystallographic directions, and so emit linear polarized PL. Since polarization properties as well as spin properties such as exchange splitting, g-factor and diamagnetic coefficient are different from dot to dot due to their size and asymmetry variations, we have carried out a statistical study of these properties in order to understand what changes occur in the QDs between these three samples. The major result from this work shows that thermal annealing of CdTe dots significantly reduces the statistical variation of exchange splittings for asymmetric dots as well as the g-factors for symmetric dots. We infer that these changes result from enlargement of the CdTe dots due to interdiffusion of Zn between the barriers and the dots. This enlargement is reflected in the increase of the median distributions of the diamagnetic shifts. Moreover, in CdSe dots, where the dot size is comparable or slightly larger than the exciton Bohr diameter, we find that the variation of these parameters is reduced as well.
Book Synopsis Investigations of Electronic Structure and Optical Properties of Ii-Vi Self-assembled Quantum Dots by : Tuan Anh Nguyen
Download or read book Investigations of Electronic Structure and Optical Properties of Ii-Vi Self-assembled Quantum Dots written by Tuan Anh Nguyen and published by . This book was released on 2006 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, we use different optical and imaging spectroscopy techniques to study electronic structure and optical properties of CdTe/ZnTe and CdSe/ZnSe self-assembled quantum dots (SAQDs). We perform single dot photoluminescence excitation experiments to identify carrier excitation mechanisms in CdTe/ZnTe QDs. The first mechanism is direct excitation into the QD excited states followed by relaxation to the ground state and the second mechanism is direct excitation into the QD ground states through LO phonon-assisted absorption. We then execute resonant PL measurements for both CdTe and CdSe QD ensembles to study the dependence of exciton-LO phonon coupling on QD size in these II-VI SAQDs. We shown that the strength of exciton-LO phonon coupling increases significantly for QDs with lateral sizes smaller than the exciton Bohr radius (e.g. as-grown CdTe QDs) while for larger QDs (e.g. CdSe or CdTe annealed) it is almost independent of the QD emission energy, and therefore presumably of the QD size. In order to study electronic coupling between SAQDs, we setup imaging experiments with the use of a hemisphere solid immersion lens. While the PLE imaging measurements show the existence two-dimensional platelets with a typical size of about 500 nm which provide spatially extended but strong localized states through which different QDs could be populated simultaneously, the spatially resolved imaging data demonstrates a complete 2D map of those platelets. These results are further supported by computational calculations based on finite element analysis. Low temperature exciton spin relaxation in symmetric CdTe SAQDs has been thoroughly studied by means of cw polarized magneto-PL and polarized time-resolved PL spectroscopies. We find that the degeneracy of exciton energy levels has a strong influence on the spin transition. When the exciton spin states in QDs are degenerate, the spin relaxation time is much shorter than the exciton recombination time. In contrast, if this degeneracy is removed, either by asymmetry or an external magnetic field, the spin relaxation time becomes much longer than the exciton recombination time. Using simple rate equation models, we estimate exciton spin relaxation times equal to 4.8 ns and 50 ps for non-degenerate and degenerate QD states, respectively.
Book Synopsis Nanotechnology Abstracts by : Eugene V. Dirote
Download or read book Nanotechnology Abstracts written by Eugene V. Dirote and published by Nova Publishers. This book was released on 2002 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanotechnology is a 'catch-all' description of activities at the level of atoms and molecules that have applications in the real world. A nanometre is a billionth of a metre, that is, about 1/80,000 of the diameter of a human hair, or 10 times the diameter of a hydrogen atom. Nanotechnology is now used in precision engineering, new materials development as well as in electronics; electromechanical systems as well as mainstream biomedical applications in areas such as gene therapy, drug delivery and novel drug discovery techniques. This book presents carefully selected abstracts of the last 5 years in this frontier field. Special access is provide by author, title and subject indexes.
Book Synopsis Advances in Condensed Matter and Materials Research by : Francois Gerard
Download or read book Advances in Condensed Matter and Materials Research written by Francois Gerard and published by Nova Publishers. This book was released on 2001 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nine articles written especially for the series synthesize international research in condensed matter. Among the topics are fiber debonding and bridging toughening in fiber-reinforced brittle matrix composites, analyzing the electron transport phenomena in high- temperature superconductivity materials by studying the band spectrum and its transformation under doping by different impurities, a functional integral approach in superconductivity theory, dye molecules in zeolite L nano crystals for efficient light harvesting, luminescent properties of some substituted 1,8 naphthyridines, and the discrete dependence of powder steels properties on porosity. No information is provided about future volumes. c. Book News Inc.
Book Synopsis State-of-the-Art of Quantum Dot System Fabrications by : Ameenah Al-Ahmadi
Download or read book State-of-the-Art of Quantum Dot System Fabrications written by Ameenah Al-Ahmadi and published by BoD – Books on Demand. This book was released on 2012-06-13 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book "State-of-the-art of Quantum Dot System Fabrications" contains ten chapters and devotes to some of quantum dot system fabrication methods that considered the dependence of shape, size and composition parameters on growth methods and conditions such as temperature, strain and deposition rates. This is a collaborative book sharing and providing fundamental research such as the one conducted in Physics, Chemistry, Material Science, with a base text that could serve as a reference in research by presenting up-to-date research work on the field of quantum dot systems.
Book Synopsis Dissertation Abstracts International by :
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2006 with total page 860 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Colloidal Quantum Dot Optoelectronics and Photovoltaics by : Gerasimos Konstantatos
Download or read book Colloidal Quantum Dot Optoelectronics and Photovoltaics written by Gerasimos Konstantatos and published by Cambridge University Press. This book was released on 2013-11-07 with total page 329 pages. Available in PDF, EPUB and Kindle. Book excerpt: Captures the most up-to-date research in the field, written in an accessible style by the world's leading experts.
Book Synopsis A Photoluminescence Scaling Study of CdSe/ZnSe Self Assembled Quantum Dots by :
Download or read book A Photoluminescence Scaling Study of CdSe/ZnSe Self Assembled Quantum Dots written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A scaling study was conducted to determine the optical properties of CdSe/ZnSe self assembled quantum dots (SAQD) as a function of changing aperture area. To accomplish this, photoluminescence (PL) experiments were performed on a sample consisting of a (100) GaAs substrate, a 1 æm ZnSe buffer layer, 3 monolayers of CdSe (forming the SAQD), and a 50 nm ZnSe capping layer through 16 apertures ranging in area from 21.76 through 0.006 æm 2 . The PL spectra from the CdSe SAQD are composed of sharp peaks seemingly dispersed on a broad feature. Two models that explain these spectral features are a single and a multiple energy state model. The multiple energy state model assumes that both the sharp peaks and the broad feature are real, distinct characteristics of the quantum dot energy landscape, while the single energy state model assumes that the broad feature is an artifact from the overlap of the individual sharp peaks. To test this the broad and the sharp features from PL spectra were isolated and the fractional integrated intensity of the features were determined for each of the aperture areas. The ratio of the sharp/broad fractional integrated intensity was then plotted as a function of changing aperture area. If the single energy state model were correct, the broad feature would vanish with a significant reduction in aperture area. This is not the case; the area of the broad feature persists for even the smallest of aperture areas. To further test the two models, several simple simulations were performed. These simulations generate a distribution of individual sharp peaks and plot their superposition. The sharp/broad fractional integrated intensity for these simulated spectra was then plotted and compared to the results from the experimental PL spectra. None of the simulation results reproduce the experimental results. When two of the simulated spectra were added together (simulating the multiple energy state model), the sharp/broad fractional integrated intensity is very similar to the experimental results. This suggests that the multiple energy state model describes the PL spectra and the CdSe SAQD energy landscape while the single energy state model does not.
Book Synopsis Encyclopedia of Optical and Photonic Engineering (Print) - Five Volume Set by : Craig Hoffman
Download or read book Encyclopedia of Optical and Photonic Engineering (Print) - Five Volume Set written by Craig Hoffman and published by CRC Press. This book was released on 2015-09-22 with total page 3726 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first edition of the Encyclopedia of Optical and Photonic Engineering provided a valuable reference concerning devices or systems that generate, transmit, measure, or detect light, and to a lesser degree, the basic interaction of light and matter. This Second Edition not only reflects the changes in optical and photonic engineering that have occurred since the first edition was published, but also: Boasts a wealth of new material, expanding the encyclopedia’s length by 25 percent Contains extensive updates, with significant revisions made throughout the text Features contributions from engineers and scientists leading the fields of optics and photonics today With the addition of a second editor, the Encyclopedia of Optical and Photonic Engineering, Second Edition offers a balanced and up-to-date look at the fundamentals of a diverse portfolio of technologies and discoveries in areas ranging from x-ray optics to photon entanglement and beyond. This edition’s release corresponds nicely with the United Nations General Assembly’s declaration of 2015 as the International Year of Light, working in tandem to raise awareness about light’s important role in the modern world. Also Available Online This Taylor & Francis encyclopedia is also available through online subscription, offering a variety of extra benefits for researchers, students, and librarians, including: Citation tracking and alerts Active reference linking Saved searches and marked lists HTML and PDF format options Contact Taylor and Francis for more information or to inquire about subscription options and print/online combination packages. US: (Tel) 1.888.318.2367; (E-mail) [email protected] International: (Tel) +44 (0) 20 7017 6062; (E-mail) [email protected]
Book Synopsis Self-Assembled Quantum Dots by : Zhiming M Wang
Download or read book Self-Assembled Quantum Dots written by Zhiming M Wang and published by Springer Science & Business Media. This book was released on 2007-11-29 with total page 470 pages. Available in PDF, EPUB and Kindle. Book excerpt: This multidisciplinary book provides up-to-date coverage of carrier and spin dynamics and energy transfer and structural interaction among nanostructures. Coverage also includes current device applications such as quantum dot lasers and detectors, as well as future applications to quantum information processing. The book will serve as a reference for anyone working with or planning to work with quantum dots.
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2540 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Semiconductor Quantum Dots by : Y. Masumoto
Download or read book Semiconductor Quantum Dots written by Y. Masumoto and published by Springer Science & Business Media. This book was released on 2013-04-17 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconductor quantum dots represent one of the fields of solid state physics that have experienced the greatest progress in the last decade. Recent years have witnessed the discovery of many striking new aspects of the optical response and electronic transport phenomena. This book surveys this progress in the physics, optical spectroscopy and application-oriented research of semiconductor quantum dots. It focuses especially on excitons, multi-excitons, their dynamical relaxation behaviour and their interactions with the surroundings of a semiconductor quantum dot. Recent developments in fabrication techniques are reviewed and potential applications discussed. This book will serve not only as an introductory textbook for graduate students but also as a concise guide for active researchers.
Book Synopsis Probing Electronic and Vibronic States in CdTe Self-assembled Quantum Dots and CdS Nanowires Using Room Temperature Resonant Raman Scattering by :
Download or read book Probing Electronic and Vibronic States in CdTe Self-assembled Quantum Dots and CdS Nanowires Using Room Temperature Resonant Raman Scattering written by and published by . This book was released on 2006 with total page 141 pages. Available in PDF, EPUB and Kindle. Book excerpt: Resonant Raman scattering (RRS) is a sensitive means to probe electronic and vibrational states in semiconductor nanostructures, even when such states are not accessible either through photoluminescence or transport techniques. In this thesis, resonant Raman scattering is used to probe the electronic and vibronic states of CdTe/ZnTe quantum dots and CdS nanowires at room temperature. In case of the CdTe/ZnTe quantum dots, the sensitivity of the ZnTe longitudinal optical phonon (LO) resonance is used to probe the excited state in the CdTe quantum dots. In addition, this technique is utilized to study the energy shifts due to post growth rapid thermal annealing. Due to annealing, both the ground and excited state energies of the quantum dots move to a higher value. This is consistent with the interdiffusion of Zn and Cd which makes the confining potential shallower and the average diameter of the quantum dots larger. In the case of the CdS nanowires, the 1-LO and 2-LO resonance is readily observed above the broad photoluminescence (PL) background. The lineshape of the integrated intensity of the 1-LO and 2-LO resembles the PL spectrum suggesting that the RRS probes the electronic states in both the ensemble and in single nanowires. In addition, the energy separation between the peaks of the 1-LO and 2-LO resonance of the ensemble CdS nanowires was found to be 34 meV which is comparable to the 37 meV value measured in bulk samples. We also show that spatially-resolved Raman scattering at resonance probes the structural uniformity in a single CdS nanowire and is able to identify the layers of the CdTe/ZnTe quantum dots sample. We found RRS intensity of single CdS nanowire strongly depends on the morphology of the wire. In conclusion, we have shown that RRS at room temperature is a sensitive and nondestructive tool to probe electronic and vibration sates as well as structural uniformity in semiconductor nanostructures.
Book Synopsis Electrical & Electronics Abstracts by :
Download or read book Electrical & Electronics Abstracts written by and published by . This book was released on 1997 with total page 2240 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Quantum Dot Sensors by : John Callan
Download or read book Quantum Dot Sensors written by John Callan and published by CRC Press. This book was released on 2013-01-24 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: Consisting of six chapters, written by experts in their field, this book charts the progress made in the use of quantum dots as the signaling component in optical sensors since their discovery in the early 1980s. In particular, it focuses on CdS-, CdSe-, and CdTe-type QDs due to their emission in the visible region of the electromagnetic spectrum.
Book Synopsis Cadmium Telluride Quantum Dots by : John Donegan
Download or read book Cadmium Telluride Quantum Dots written by John Donegan and published by CRC Press. This book was released on 2016-04-19 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the last two decades, semiconductor quantum dots-small colloidal nanoparticles-have garnered a great deal of scientific interest because of their unique properties. Among nanomaterials, CdTe holds special technological importance as the only known II-VI material that can form conventional p-n junctions. This makes CdTe very important for the dev
Book Synopsis CdTe/ZnTe Quantum Dots - Growth and Optical Properties by : Sebastian Mackowski
Download or read book CdTe/ZnTe Quantum Dots - Growth and Optical Properties written by Sebastian Mackowski and published by . This book was released on 2002 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper gives an overview of molecular beam epitaxy (MBE) growth of and the optical properties of Cadmium Telluride (CdTe) quantum dots grown on Zinc Telluride (ZnTe) by self-assembly. It is shown that quantum dots in this material system can be obtained either by depositing CdTe at a high substrate temperature or by subjecting CdTe layer to a healing process, up to 70 seconds long before its capping or, eventually, by applying these two methods simultaneously. Moreover, it is found that one can also use the atomic layer epitaxy method to achieve the formation. From optical measurements performed on large quantum dot ensembles it is found that the quantum dot emission is much broader than that of quantum wells, and that it is observable up to much higher temperatures, which indicates strong exciton localization. The latter is also evidenced by an insensitivity of the decay time of the exciton recombination (^3O0 ps) to the temperature. From the presence of a second, very long decay time (^5 ns) and from disappearance of the sharp lines related to recombination in single dots, the acoustic phonon scattering of excitons is found to play an important role in these quantum dot structures. From a magnetic field dependence of the single dot emission energy, the exciton effective g-factor and spatial extension of the exciton wave function are deduced to be equal to -3 and 3 nanometers, respectively. Both the g-factor and the value of the diamagnetic shift are found to be independent of the energy of the quantum dot emission at Beta=Omicron Tau and of the in-plane symmetry of its potential. (11 figures, 35 refs.).
