A Theoretical Study of Carrier Dynamics in Semiconductor Quantum Dots PDF Download
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Author: Marta Cundin
Publisher:
ISBN:
Category :
Languages : en
Pages : 334
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Book Description
Author: Marta Cundin
Publisher:
ISBN:
Category :
Languages : en
Pages : 334
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Book Description
Author: Y. Masumoto
Publisher: Springer Science & Business Media
ISBN: 3662050013
Category : Technology & Engineering
Languages : en
Pages : 500
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Book Description
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.
Author: Ladislaus Alexander Banyai
Publisher: World Scientific
ISBN: 9814504238
Category : Science
Languages : en
Pages : 264
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Book Description
Semiconductor Quantum Dots presents an overview of the background and recent developments in the rapidly growing field of ultrasmall semiconductor microcrystallites, in which the carrier confinement is sufficiently strong to allow only quantized states of the electrons and holes. The main emphasis of this book is the theoretical analysis of the confinement induced modifications of the optical and electronic properties of quantum dots in comparison with extended materials. The book develops the theoretical background material for the analysis of carrier quantum-confinement effects, introduces the different confinement regimes for relative or center-of-mass motion quantization of the electron-hole-pairs, and gives an overview of the best approximation schemes for each regime. A detailed discussion of the carrier states in quantum dots is presented and surface polarization instabilities are analyzed, leading to the self-trapping of carriers near the surface of the dots. The influence of spin-orbit coupling on the quantum-confined carrier states is discussed. The linear and nonlinear optical properties of small and large quantum dots are studied in detail and the influence of the quantum-dot size distribution in many realistic samples is outlined. Phonons in quantum dots as well as the influence of external electric or magnetic fields are also discussed. Last but not least the recent developments dealing with regular systems of quantum dots are also reviewed. All things included, this is an important piece of work on semiconductor quantum dots not to be dismissed by serious researchers and physicists.
Author: 蘇立杰
Publisher:
ISBN:
Category :
Languages : en
Pages : 85
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Book Description
Author: Tobias Nowozin
Publisher: Springer Science & Business Media
ISBN: 3319019708
Category : Technology & Engineering
Languages : en
Pages : 163
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Book Description
Today’s semiconductor memory market is divided between two types of memory: DRAM and Flash. Each has its own advantages and disadvantages. While DRAM is fast but volatile, Flash is non-volatile but slow. A memory system based on self-organized quantum dots (QDs) as storage node could combine the advantages of modern DRAM and Flash, thus merging the latter’s non-volatility with very fast write times. This thesis investigates the electronic properties of and carrier dynamics in self-organized quantum dots by means of time-resolved capacitance spectroscopy and time-resolved current measurements. The first aim is to study the localization energy of various QD systems in order to assess the potential of increasing the storage time in QDs to non-volatility. Surprisingly, it is found that the major impact of carrier capture cross-sections of QDs is to influence, and at times counterbalance, carrier storage in addition to the localization energy. The second aim is to study the coupling between a layer of self-organized QDs and a two-dimensional hole gas (2DHG), which is relevant for the read-out process in memory systems. The investigation yields the discovery of the many-particle ground states in the QD ensemble. In addition to its technological relevance, the thesis also offers new insights into the fascinating field of nanostructure physics.
Author: Gero Nootz
Publisher:
ISBN:
Category : Quantum dots
Languages : en
Pages : 113
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Book Description
The aim of this dissertation is to gain a better understanding of the unique electronic structure of lead salt quantum dots (QDs) and its influences on the nonlinear optical (NLO) properties as well as the time dynamics of the photogenerated charge carriers. A variety of optical techniques such as Z-scan, two-photon excited fluorescence and time-resolved pump probe spectroscopy are used to measure these properties. The one-photon as well as the degenerate and nondegenerate two-photon absorption (2PA) spectra are measured and the electronic wave functions from a four-band envelope function formalism are used to model the results. We observe local maxima in the 2PA spectra for QD samples of many different sizes at energies where only 1PA is predicted by the model. This is similar to the previously measured transitions in the 1PA spectra which are not predicted by the model but accrue at the energies of the two-photon allowed transitions. Most importantly we observe 2PA peaks for all samples at the energy of the first one-photon allowed transition. This result can only be understood in terms of symmetry breaking and therefore is strong evidence that other transitions, not predicted by the model if the selection rules are left intact, also have the origin in the lifted spatial symmetry of the wave functions. On the other hand, the uniquely symmetric eigenenergies of these quantum-confined energy states in the conduction and valance bands explain the observed trend toward larger two-photon cross-sections as the quantum confinement is increased in smaller QDs. Moreover, this unique feature is shown to reduce the possible relaxation channels for photoexcited carriers, which is confirmed experimentally by the reduced carrier relaxation rate as compared to CdSe QDs which lack this symmetry. Carrier multiplication (CM), a process in which several electrons are excited by the absorption of a single photon is studied in PbS QDs. We show that for PbS QDs with radius smaller than 2.5 nm the parameters of CM get very close to the theoretical optimum. Next-generation solar cells operating under these ideal conditions could potentially have conversion efficiency of up to 42%. This compares favorably to the 30% efficiency limit of a single junction silicon solar cell.
Author: Pooja Tyagi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"Due to the large surface-to-volume ratio of quantum dots, their surface conditions play a significant role in determining their electronic and optical properties. In this thesis, we show that the presence of surface states modifies the optical selection rules in quantum dots and enhances the rate of surface charge trapping. These surface-induced effects have profound impact on the measurement of multiexciton recombination and carrier multiplication processes. Specifically, in transient absorption studies, surface states result in additional decay timescales which may be misattributed to multiexciton recombination processes. Additionally, they lead to large "apparent" carrier multiplication yields even under conditions where it is forbidden by energy conservation. The surface-dependent transient absorption studies presented in this work suggest ways to identify and minimize the undesirable surface-induced signals. Interestingly, surface-induced processes also result in significant electrostatic effects. We show that due to the piezoelectric nature of wurtzite CdSe quantum dots, the strong electric field created by surface charge trapping can drive coherent acoustic phonons in these systems. We further show that the amplitude of this piezoelectric response can be controlled by altering the surface conditions of the quantum dot. Finally, we theoretically investigate the effect of multiple surface layers on carrier localization in nanostructures. We find that in a core/barrier/shell configuration, layered nanostructures offer independent control over electron and hole wave functions. These results suggest design principles for wave function engineering in potential quantum dot applications in light emitting devices, photovoltaics and optical amplification." --
Author: Rosa Leon
Publisher: Cambridge University Press
ISBN: 9781107412927
Category : Technology & Engineering
Languages : en
Pages : 402
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Book Description
This book confirms the high level of international interest in understanding and control the properties of semiconductor quantum-dot structures and devices. It highlights the self-assembled (self-forming) type of quantum dots that result from the islanding transition in strained heteroepitaxy of III-V semiconductors. It also features nanocrystals, colloidal dots and biological applications. Technological applications span quantum-dot laser diodes, quantum-dot optical amplifiers, biosensing applications, infrared photodetectors, photovoltaic devices, quantum cellular automata and magnetic semiconductors. It reports the development by researchers at the Johannes Kepler University in Linz of a mid-infrared, vertical cavity surface emitting quantum dot (QD) using the lead salt compounds PbSe and PbEuTe; optical gain and stimulated emission in colloidal quantum dots and the use of quantum dots for optical amplifiers reported by researchers at the National Institute of Standards and Technology in Boulder. Topics include: theory, modeling and simulations; nanocrystals, colloidal dots and biological applications; quantum-dot-based devices and transport studies; carrier dynamics and interactions and energy relaxation and single-dot spectroscopy.
Author: Gerasimos Konstantatos
Publisher: Cambridge University Press
ISBN: 0521198267
Category : Science
Languages : en
Pages : 329
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Book Description
Captures the most up-to-date research in the field, written in an accessible style by the world's leading experts.
Author: Andrey Rogach
Publisher: Springer Science & Business Media
ISBN: 3211752374
Category : Technology & Engineering
Languages : en
Pages : 374
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Book Description
This is the first book to specifically focus on semiconductor nanocrystals, and address their synthesis and assembly, optical properties and spectroscopy, and potential areas of nanocrystal-based devices. The enormous potential of nanoscience to impact on industrial output is now clear. Over the next two decades, much of the science will transfer into new products and processes. One emerging area where this challenge will be very successfully met is the field of semiconductor nanocrystals. Also known as colloidal quantum dots, their unique properties have attracted much attention in the last twenty years.
