Charge Carrier Dynamics and the Development of Optical Gain in Semiconductor Quantum Dots PDF Download

Author: Ryan R. Cooney
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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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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Captures the most up-to-date research in the field, written in an accessible style by the world's leading experts.

Author: Golam Bappi
Publisher:
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Languages : en
Pages :

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Colloidal quantum dots have seen progress over the last three decades as an active material for solution processed optoelectronics. Quantum dots offer a tunable optical bandgap from the UV to the mid-IR via control over size and chemical composition. Their optical and electronic properties can be further manipulated through surface engineering and heterostructuring. These materials are processed from solution, enabling low-cost fabrication; and are compatible with a wide range of substrates.In this thesis, I investigate properties of colloidal quantum dots for lasing applications. My findings illuminate fundamental processes that determine their performance in lasing; and point to strategies to overcome present-day limitations. First, I investigate the effects of temperatures reached during continuous-wave excitation on the charge carrier dynamics in CdSe/CdS core/shell QDs, and their effect on the lasing threshold. Modelling and experimental characterization reveal a temperature-activated sub- picosecond electron trapping process that depletes the population of excited QDs. Accordingly, a small decrease in the athermal lasing threshold can yield a large decrease in the continuous- wave lasing threshold due to reduced heat generation. In CdSe/CdS QDs, built-in biaxial strain reduces the valence band-edge degeneracy, lowering the athermal and CW lasing threshold by 30% and 70% respectively. Next I investigate graded CdSe/CdS shells on infrared InAs QDs to suppress non-radiative biexciton Auger recombination. Infrared InAs QDs are promising materials for infrared light emitting devices, but their Auger lifetime is much shorter than those found in more widely explored cadmium and lead chalcogenide materials. The graded CdSe/CdS shells on InAs which I develop herein result in a 2x increase in the Auger lifetime relative to the best value reported in prior InAs QD literature. Finally, I propose a method to achieve nanosecond deep-blue lasing using CsPbCl3 QDs. These perovskite quantum dots suffer from fast biexciton Auger lifetimes, and are consequently able to sustain lasing only under femtosecond pulsed photoexcitation. Forming a superlattice of QDs with aligned dipoles, and coupling them to a high Q-factor distributed feedback grating, is a step toward quasi-CW lasing in this materials system. I design the grating for single mode operation within the gain spectrum of the CsPbCl3 QDs.

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: Rachel Hoffman Gilmore
Publisher:
ISBN:
Category :
Languages : en
Pages : 117

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Quantum dots, also called semiconductor nanocrystals, are an interesting class of materials because their band gap is a function of the quantum dot size. Their optical properties are not determined solely by the atomic composition, but may be engineered. Advances in quantum dot synthesis have enabled control of the ensemble size dispersity and the creation of monodisperse quantum dot ensembles with size variations of less than one atomic layer. Quantum dots have been used in a variety of applications including solar cells, light-emitting diodes, photodetectors, and thermoelectrics. In many of these applications, understanding charge transport in quantum dot solids is crucial to optimizing efficient devices. We examine charge transport in monodisperse, coupled quantum dot solids using spectroscopic techniques explained by hopping transport models that provide a complementary picture to device measurements. In our monodisperse quantum dot solids, the site-to-site energetic disorder that comes from size dispersity and the size-dependent band gap is very small and spatial disorder in the quantum dot superlattice often has a greater impact on charge transport. In Chapter 2, we show that improved structural order from self-assembly in monodisperse quantum dots reduces the interparticle spacing and has a greater impact than reduced energetic disorder on increasing charge carrier hopping rates. In Chapter 3, we present temperature-dependent transport measurements that demonstrate again that when energetic disorder is very low, structural changes will dominate the dynamics. We find increasing mobility with decreasing temperature that can be explained by a 1-2 Å contraction in the edge-to-edge nearest neighbor quantum dot spacing. In Chapter 4, we study optical states that are 100-200 meV lower in energy than the band gap. Because we work with monodisperse quantum dots, we are able to resolve this trap state separately from the band edge state and study its optical properties. We identify the trap state as dimers that form during synthesis and ligand exchange when two bare quantum dot surfaces fuse. The findings of this thesis point to the importance of minimizing the structural disorder of the coupled quantum dot solid in addition to the energetic disorder to optimize charge carrier transport.

Author: Pooja Tyagi
Publisher:
ISBN:
Category :
Languages : en
Pages :

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"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:
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Category :
Languages : en
Pages : 4

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Low-dimensional semiconductors have attracted great interest due to the potential for tailoring their linear and nonlinear optical properties over a wide-range. Semiconductor nanocrystals (NC's) represent a class of quasi-zero-dimensional objects or quantum dots. Due to quantum cordhement and a large surface-to-volume ratio, the linear and nonlinear optical properties, and the carrier dynamics in NC's are significantly different horn those in bulk materials. napping at surface states can lead to a fast depopulation of quantized states, accompanied by charge separation and generation of local fields which significantly modifies the nonlinear optical response in NC's. 3D carrier confinement also has a drastic effect on the energy relaxation dynamics. In strongly confined NC's, the energy-level spacing can greatly exceed typical phonon energies. This has been expected to significantly inhibit phonon-related mechanisms for energy losses, an effect referred to as a phonon bottleneck. It has been suggested recently that the phonon bottleneck in 3D-confined systems can be removed due to enhanced role of Auger-type interactions. In this paper we report femtosecond (fs) studies of ultrafast optical nonlinearities, and energy relaxation and trap ping dynamics in three types of quantum-dot systems: semiconductor NC/glass composites made by high temperature precipitation, ion-implanted NC's, and colloidal NC'S. Comparison of ultrafast data for different samples allows us to separate effects being intrinsic to quantum dots from those related to lattice imperfections and interface properties.

Author: Peter Michler
Publisher: Springer Science & Business Media
ISBN: 3540874461
Category : Technology & Engineering
Languages : en
Pages : 390

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Book Description
This book reviews recent advances in the field of semiconductor quantum dots via contributions from prominent researchers in the scientific community. Special focus is given to optical, quantum optical, and spin properties of single quantum dots.

Author: Stefan Meinecke
Publisher: Springer Nature
ISBN: 3030962482
Category : Technology & Engineering
Languages : en
Pages : 264

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Book Description
This thesis investigates passively mode-locked semiconductor lasers by numerical methods. The understanding and optimization of such devices is crucial to the advancement of technologies such as optical data communication and dual comb spectroscopy. The focus of the thesis is therefore on the development of efficient numerical models, which are able both to perform larger parameter studies and to provide quantitative predictions. Along with that, visualization and evaluation techniques for the rich spatio-temporal laser dynamics are developed; these facilitate the physical interpretation of the observed features. The investigations in this thesis revolve around two specific semiconductor devices, namely a monolithically integrated three-section tapered quantum-dot laser and a V-shaped external cavity laser. In both cases, the simulations closely tie in with experimental results, which have been obtained in collaboration with the TU Darmstadt and the ETH Zurich. Based on the successful numerical reproduction of the experimental findings, the emission dynamics of both lasers can be understood in terms of the cavity geometry and the active medium dynamics. The latter, in particular, highlights the value of the developed simulation tools, since the fast charge-carrier dynamics are generally not experimentally accessible during mode-locking operation. Lastly, the numerical models are used to perform laser design explorations and thus to derive recommendations for further optimizations.