Download or read book Charge Carrier Dynamics in Nontoxic Semiconductor Quantum Dots written by Alexander Florian Richter and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Charge Carrier Dynamics and the Development of Optical Gain in Semiconductor Quantum Dots written by Ryan R. Cooney and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Charge Carrier Dynamics in Lead Sulfide Quantum Dot Solids written by Rachel Hoffman Gilmore and published by . This book was released on 2017 with total page 117 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Effects of Surface and Chemical Composition on the Charge Carriers of Alloyed Quantum Dots written by Joseph Daniel Keene and published by . This book was released on 2015 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Surface Effects on Charge Carrier Dynamics in Semiconductor Quantum Dots written by Pooja Tyagi and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "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." --
Download or read book Carrier Dynamics in Semiconductor Quantum Dots written by Jörg Siegert and published by . This book was released on 2006 with total page 99 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Self Organized Quantum Dots for Memories written by Tobias Nowozin and published by Springer. This book was released on 2016-08-27 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Ultrafast Carrier Dynamics in Semiconductor Self assembled Quantum Dots in the Low Carrier Density Regime written by Junji Urayama and published by . This book was released on 2002 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Charge Carrier Dynamics in Colloidal Quantum Dots written by and published by . This book was released on 2015 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Semiconductor Quantum Dots written by Yasuaki Masumoto and published by Springer Science & Business Media. This book was released on 2002-05-28 with total page 520 pages. Available in PDF, EPUB and Kindle. Book excerpt: Growth of Self Organized Quantum Dots / J.-S. Lee / - Excitonic Structures and Optical Properties of Quantum Dots / Toshihide Takagahara / - Electron-Phonon Interactions in Semiconductor Quantum Dots / Toshihide Takagahara / - Micro-Imaging and Single Dot Spectroscopy of Self Assembled Quantum Dots / Mitsuru Sugisaki / - Persistent Spectral Hole Burning in Semiconductor Quantum Dots / Yasuaki Masumoto / - Dynamics of Carrier Relaxation in Self Assembled Quantum Dots / Ivan V. Ignatiev, Igor E. Kozin / - Resonant Two-Photon Spectroscopy of Quantum Dots / Alexander Baranov / - Homogeneous Width of Confined Excitons in Quantum Dots - Experimental / Yasuaki Masumoto / - Theory of Exciton Dephasing in Semiconductor Quantum Dots / Toshihide Takagahara / - Excitonic Optical Nonlinearity and Weakly Correlated Exciton-Pair States / Selvakumar V. Nair, Toshihide Takagahara / - Coulomb Effects in the Optical Spectra of Highly Excited Semiconductor Quantum Dots / Selvakumar V. Nair / - Device ...
Download or read book Semiconducting Nanocrystals Synthesis Colloidal Stability and Charge Carrier Dynamics written by Shuai Chen and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal nanocrystals (NCs) with controllable morphologies and sizes are at the core of nanomaterials research. Among different NCs (zero-dimensional quantum dots, one-dimensional nanorods, etc.), two-dimensional cadmium selenide (CdSe) nanoplatelets (NPLs) with lateral extension of over 100 nm2 and atomically precise thickness are one of the most promising semiconductors for optoelectronic applications. However, several issues remain for implementing CdSe NPLs for applications, including: (1) containing toxic and heavy elements, and (2) lacking a fundamental understanding of the colloidal stability and the process of charge carrier generation in solids. This thesis aims to synthesize environmentally friendly alternatives, such as indium phosphide (InP) NCs with varied shapes, and shed light on colloidal stability and charge carrier generation and dynamics using conventional CdSe NPLs as the model system. The introductory Chapter 1 briefly presents an overview of nanomaterials and nanotechnology, including quantum confinement in NCs, quantum dots, InP NCs, the synthesis status of CdSe NPLs, colloidal NCs stabilization in dispersion, photophysics of CdSe NPLs, ligand exchange method, and the thermal annealing method. In Chapter 2, we introduce terahertz (THz) spectroscopy basics, including the generation and detection mechanism, experimental setups, and the conductivity models for data analysis to infer charge transport properties in materials of interest. Chapters 3-5 present the key results of this thesis. In Chapter 3, we synthesize InP NCs with different shapes and sizes by utilizing triphenyl phosphite as the phosphorus source. We show that InP NCs can be synthesized and formed from In2O3 NCs. Our findings open new synthetic possibilities by utilizing a cost-effective, non-pyrophoric, and non-toxic phosphorus precursor. In Chapter 4, we combine THz photoconductivity measurements with simulations to study the colloidal stability and aggregation process in CdSe NPL dispersion. We demonstrate that increasing the facet area of NPLs and the solvent length can reduce the critical concentration at which NPLs start aggregating. Our simulation attributes the effect to the solvation force-dominated colloidal stability for the NPL system; the solvation force is enhanced by increasing the NPL lateral area and the length of solvent molecules. In Chapter 5, we report that thermal annealing constitutes an effective strategy to control the optical absorption and electrical properties of CdSe NPLs by tuning the inter-NPL distance. We observe a direct correlation between the temperature-dependent ligand decomposition and the NPL-NPL distance shortening (by TEM). This leads to a strong red-shift in the absorption band edge (by UV-vis studies) and enhanced electrical transport Abstract in NPL films. Our results illustrate a straightforward manner to control the interfacial electronic coupling strength for developing functional optoelectronics through thermal treatments.
Download or read book Non Markovian Quantum Dynamics of Charge Carriers in Open Quantum Dots written by Eduardo Vicente Vaz and published by . This book was released on 2010 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Optical Nonlinearities and Ultrafast Carrier Dynamics in Semiconductor Quantum Dots written by and published by . This book was released on 1998 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Time Resolved Electronic Relaxation Processes in Self Organized Quantum Dots written by and published by . This book was released on 2005 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: The authors have performed a comprehensive set of experiments on the dynamics of electrons and holes in semiconductor quantum dots, and a complete picture of the dynamics as a function of carrier density and temperature has emerged. Specifically, they have used two- and three-pulse femtosecond differential transmission spectroscopy to study the dependence of quantum dot carrier dynamics on temperature. At low temperatures and densities, the rates for relaxation between the quantum dot confined states and for capture from the barrier region into the various dot levels could be directly determined. For electron-hole pairs generated directly in the quantum dot excited state, relaxation is dominated by electron-hole scattering, and occurs on a 5-ps time scale. Capture times from the barrier into the quantum dot are on the order of 2 ps (into the excited state) and 10 ps (into the ground state). The phonon bottleneck was clearly observed in low-density capture experiments, and the conditions for its observation (namely, the suppression of electron-hole scattering for non-geminately captured electrons) were determined. As temperature increases beyond about 100 K, the dynamics become dominated by the reemission of carriers from the lower dot levels due to the large density of states in the wetting layer and barrier region. Measurements of the gain dynamics show fast (130-fs) gain recovery due to intradot carrier-carrier scattering, and picosecond-scale capture. Direct measurement of the transparency density versus temperature shows the dramatic effect of carrier reemission for the quantum dots to thermally activated scattering. The carrier dynamics at elevated temperatures are thus strongly dominated by the high density of the high-energy continuum states relative to the dot-confined levels. Deleterious hot carrier effects can be suppressed in quantum dot lasers by resonant tunneling injection.
Download or read book Quantum Control of Charge Carrier Dynamics in Layered Semiconductor Heterostructures written by Kevin L. Shuford and published by . This book was released on 2003 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Theoretical Study of Carrier Dynamics in Semiconductor Quantum Dots written by Marta Cundin and published by . This book was released on 2004 with total page 334 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Semiconductor Quantum Dots written by Ladislaus B nyai and published by World Scientific. This book was released on 1993 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
