Download or read book Size Dependent Optoelectronic Properties and Controlled Doping of Semiconductor Quantum Dots written by Jesse Hart Engel and published by . This book was released on 2013 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt: Given a rapidly developing world, the need exists for inexpensive renewable energy alternatives to help avoid drastic climate change. Photovoltaics have the potential to fill the energy needs of the future, but significant cost decreases are necessary for widespread adoption. Semiconductor nanocrystals, also known as quantum dots, are a nascent technology with long term potential to enable inexpensive and high efficiency photovoltaics. When de- posited as a film, quantum dots form unique nanocomposites whose electronic and optical properties can be broadly tuned through manipulation of their individual constituents. The contents of this thesis explore methods to understand and optimize the optoelectronic properties of PbSe quantum dot films for use in photovoltaic applications. Systematic optimization of photovoltaic performance is demonstrated as a function of nanocrystal size, establishing the potential for utilizing extreme quantum confinement to improve device energetics and alignment. Detailed investigations of the mechanisms of electrical transport are performed, revealing that electronic coupling in quantum dot films is significantly less than often assumed based on optical shifts. A method is proposed to employ extended regions of built-in electrical field, through controlled doping, to sidestep issues of poor transport. To this end, treatments with chemical redox agents are found to effect profound and reversible doping within nanocrystal films, sufficient to enable their use as chemical sensors, but lack- ing the precision required for optoelectronic applications. Finally, a novel doping method employing "redox buffers" is presented to enact precise, stable, and reversible charge-transfer doping in porous semiconductor films. An example of oxidatively doping PbSe quantum dot thin films is presented, and the future potential for redox buffers in photovoltaic applications is examined.
Download or read book Complementary Tuning Semiconductor NCs Properties Using Precursor Reactivity Doping and Post synthetic Modification written by Mohammad Sadegh Yadanparast and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Quantum dots are nanocrystalline semiconductors in which the size is so small that optoelectronic properties are size dependent. QDs have a lot of applications in displays, solar cells, lasers, light emitting diodes, etc. The optoelectronic properties of QDs depend on their size, composition, the shape of the particles and also the surface chemistry of the QDs. Phosphine based precursors have been mostly used in the synthesis of QDs. Due to the lack of tunable reactivity, this class of precursors, QDs with different shape are obtained by under different reaction conditions. With that, branched QDs are less likely to be obtained in one step reaction using phosphine based precursors. To synthesis QDs with a branched structure, in a single step synthesis, mixtures of precursors with different reactivity were used. Using dichalcogenides mixture, CdSe1-xSx hyperbranched supra-quantum dots (HSQDs) where synthesized in a one-step microwave-assisted synthesis and shape evolution mechanism of formation of NCs studied. It is shown that the NCs formed in three steps of nucleation, aggregation, and growth. By controlling the reaction conditions, simple branched tetrapod NCs are prepared, but the obtained NCs have no emission due to unpassivated surface and defects which work as trap. To obtain luminescent NCs obtained through doping. Hyperbranched Mn2+:ZnSe1-xSx NCs also prepared using a mixture of Ph2Se2 and Me2S2. The shape evolution mechanism of the formation of NCs was studied and it is shown that the NCs are formed via oriented attachment of initially formed nanoparticles. The NCs used for thiol sensing, and it observed that they have a better sensitivity and detection limit than spherical QDs. Although hyperbranched NCs have higher sensitivities over nonbranched NCs but, the spherical NCs have better detection limit and can dispersed in aqueous medium by ZnS shell growth followed by silica shell formation. To study the effect of ZnS shell thickness on sensing property of NCs, a set of spherical Mn:ZnSe@ZnS with different ZnS shell thickness were prepared and used for thiol sensing. It observed that in organic medium, thinner ZnS layer gives the highest sensitivity and QDs with thick ZnS shell layer have less sensitivity. For measurement in aqueous medium, QDs transferred to PBS buffer after formation of silica shell over QDs. It observed that NCs with a thin ZnS shell layer lose their emission and sensing completely. Thick ZnS shell protects NCs in the silica shell formation step but they show very low sensitivity to thiol compounds as well. ZnS shell with medium thickness gives the best sensitivity in an aqueous medium. The emission of Mn:ZnSe@ZnS QDs originated from d-d electron transition of Mn(II) ions and is independent to the size of QDs. To extend our study to QDs with band edge emission, preparation of luminescent InP QDs by post-synthetic modification is studied. InP NCs were synthesized using heat up method and successive injection of precursors. Narrow size distribution NCs obtained after size selection precipitation. Emissive NCs obtained after etching using InCl3 and fluoride containing salts. The study showed that more InCl3 case more etching and presence of fluoride-containing salt is necessary for band edge emission of the NCs.
Download or read book Quantum Dot Optoelectronic Devices written by Peng Yu and published by Springer Nature. This book was released on 2020-04-16 with total page 329 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book captures cutting-edge research in semiconductor quantum dot devices, discussing preparation methods and properties, and providing a comprehensive overview of their optoelectronic applications. Quantum dots (QDs), with particle sizes in the nanometer range, have unique electronic and optical properties. They have the potential to open an avenue for next-generation optoelectronic methods and devices, such as lasers, biomarker assays, field effect transistors, LEDs, photodetectors, and solar concentrators. By bringing together leaders in the various application areas, this book is both a comprehensive introduction to different kinds of QDs with unique physical properties as well as their preparation routes, and a platform for knowledge sharing and dissemination of the latest advances in a novel area of nanotechnology.
Download or read book Semiconductor Nanocrystals written by Alexander L. Efros and published by Springer Science & Business Media. This book was released on 2013-06-29 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt: A physics book that covers the optical properties of quantum-confined semiconductor nanostructures from both the theoretical and experimental points of view together with technological applications. Topics to be reviewed include quantum confinement effects in semiconductors, optical adsorption and emission properties of group IV, III-V, II-VI semiconductors, deep-etched and self assembled quantum dots, nanoclusters, and laser applications in optoelectronics.
Download or read book Quantum Dot single Wall Carbon Nanotube Complexes for Tunable Optoelectronic Microsystems Sensors written by Brian J. Landi and published by . This book was released on 2006 with total page 396 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Quantum dot-single wall carbon nanotube (QD-SWNT) complexes have been investigated for use in optoelectronic applications. Quantum confinement effects imbue size-dependent properties in nanomaterials which can be controlled during synthesis and exploited in devices. The physical properties inherent to semiconducting quantum dots (QDs) and single-wall carbon nanotubes (SWNTs) render their chemical combination a unique nanomaterial complex for Microsystems. Synthesis proficiency has been demonstrated for two techniques: (1) a pulsed laser vaporization process for SWNTs, and (2) wet chemistry colloidal approaches for CdSe and CuInS2 QDs. A significant fraction of the work in this Dissertation has been devoted to establishing standardized protocols for characterizing the nanomaterial properties using electron microscopy and spectroscopy. In the case of SWNTs, innovative methods have been developed to accurately assess the SWNT purity and monitor the purification steps during thermal oxidation. These results represent the first established metrics of reference for SWNT purity as well as unprecedented levels of purification efficiency. Experimental control over SWNT chiral distributions and QD particle diameter has shown where the size-dependent tunability of their optical bandgap can be used for selective absorption and emission based upon size and structure. Modification of the surface ligands on the QDs has facilitated an investigation of chemical attachment procedures to high purity SWNTs using covalent, electrostatic, and noncovalent reaction schemes. Polymeric photodiodes utilizing successful QD-SWNT complexes were fabricated and have shown the ability for select optical absorption, exciton dissociation, and charge transport. Thus, QD-SWNT complexes represent a new class of nanomaterials which are expected to impact Microsystems optoelectronic applications (e.g.color sensors, lab-on-a-chip spectrometry, smart pixels, etc.) due to wavelength selectivity, absorption sensitivity, and potential for nanoscale fabrication"--Abstract.
Download or read book Nanocrystal Quantum Dots written by Victor I. Klimov and published by CRC Press. This book was released on 2017-12-19 with total page 485 pages. Available in PDF, EPUB and Kindle. Book excerpt: A review of recent advancements in colloidal nanocrystals and quantum-confined nanostructures, Nanocrystal Quantum Dots is the second edition of Semiconductor and Metal Nanocrystals: Synthesis and Electronic and Optical Properties, originally published in 2003. This new title reflects the book’s altered focus on semiconductor nanocrystals. Gathering contributions from leading researchers, this book contains new chapters on carrier multiplication (generation of multiexcitons by single photons), doping of semiconductor nanocrystals, and applications of nanocrystals in biology. Other updates include: New insights regarding the underlying mechanisms supporting colloidal nanocrystal growth A revised general overview of multiexciton phenomena, including spectral and dynamical signatures of multiexcitons in transient absorption and photoluminescence Analysis of nanocrystal-specific features of multiexciton recombination A review of the status of new field of carrier multiplication Expanded coverage of theory, covering the regime of high-charge densities New results on quantum dots of lead chalcogenides, with a focus studies of carrier multiplication and the latest results regarding Schottky junction solar cells Presents useful examples to illustrate applications of nanocrystals in biological labeling, imaging, and diagnostics The book also includes a review of recent progress made in biological applications of colloidal nanocrystals, as well as a comparative analysis of the advantages and limitations of techniques for preparing biocompatible quantum dots. The authors summarize the latest developments in the synthesis and understanding of magnetically doped semiconductor nanocrystals, and they present a detailed discussion of issues related to the synthesis, magneto-optics, and photoluminescence of doped colloidal nanocrystals as well. A valuable addition to the pantheon of literature in the field of nanoscience, this book presents pioneering research from experts whose work has led to the numerous advances of the past several years.
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.
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.
Download or read book Core Shell Quantum Dots written by Xin Tong and published by Springer Nature. This book was released on 2020-07-01 with total page 331 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book outlines various synthetic approaches, tuneable physical properties, and device applications of core/shell quantum dots (QDs). Core/shell QDs have exhibited enhanced quantum yield (QY), suppressed photobleaching/blinking, and significantly improved photochemical/physical stability as compared to conventional bare QDs. The core-shell structure also promotes the easy tuning of QDs’ band structure, leading to their employment as attractive building blocks in various optoelectronic devices. The main objective of this book is to create a platform for knowledge sharing and dissemination of the latest advances in novel areas of core/shell QDs and relevant devices, and to provide a comprehensive introduction and directions for further research in this growing area of nanomaterials research.
Download or read book Designing Quantum Dot Solids for Optoelectronic Devices Through Matrix Engineering written by Jason Tolentino and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal quantum dot (CQD) solids represent a class of materials that allows one to control the optical and electronic properties due to their unique size-dependent properties with special electronic and optoelectronic device applications. Unfortunately, integration of these materials into high performing devices such as transistors and solar cells have been challenging due to: 1) uncontrolled environmental stability 2) lack of accurate control over charge carrier type and mobility 3) poor device operational stability and 4) limited experimental methods to probe the density of states in these materials in order to understand fundamental electronic and optical properties. In this thesis, we demonstrate the ability to stabilize and improve the environmental stability of these materials with amorphous Al2O3 (a-alumina). More importantly, we can accurately engineer the carrier type and mobility by varying the thickness of the alumina. Through a combination of small, compact inorganic ligands and the ability to passivate surface electronic traps, air-stable, high electron mobility PbSe QD field-effect transistors (FET) are obtained. We then show that we can also improve transistor device operational stability through an in-vacuo ligand exchange with H2S gas introduced in an atomic layer deposition (ALD) chamber. We find that this method is universal when volatile ligands are used. Possible mechanisms for device instability will be discussed such as proton migration and trap passivation. Using an optimized film preparation, this work will be the first demonstration of a QD FET with an electron mobility greater than 10 cm2 V-1 s-1 that is also operationally stable. Finally, we introduce a unique transmission spectroscopy technique of field-effect transistors to electrostatically probe induced charge carriers in PbSe QD films. With this technique we resolve occupation of quantized states of the quantum dots rather than the matrix or interfacial states. This platform is used to test fundamental transport models as it relates to disordered semiconductors such as QDs. From this technique, we can draw important conclusions about charge transport at room temperature. This novel experimental method can be extended to other experimental setups such as photoluminescence and photoconductivity in order to understand how to rationally improve the electronic properties of QD films.
Download or read book Quantum Dots Theory and Applications written by Rodolph Donovan and published by . This book was released on 2016-04-01 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: A quantum dot is a nanoparticle made of any semiconductor material such as silicon, cadmium selenide, cadmium sulfide, or indium arsenide. Quantum dots may be able to increase the efficiency of solar cells. In normal solar cells, a photon of light generates one electron. Experiments with both silicon quantum dots and lead sulfide quantum dots can generate two electrons for a single photon of light. Therefore, using quantum dots in solar cells could significantly increase their efficiency in producing electric power. Quantum dots (QD) are nanoscale semiconductor devices that tightly confine either electrons or electron holes in all three spatial dimensions. They can be made through several possible routes including colloidal synthesis, plasma synthesis, or mechanical fabrication. The electronic properties of the quantum dots fall between those of bulk semiconductors and those of discrete molecules of comparable size, and optoelectronic properties such as band gap, can be tuned as a function of particle size and shape for a given composition. Because of the high tunability of properties, QDs are of interest in many research applications such as transistors, solar cells, LEDs, and diode lasers. For instance, the ability of QDs to precisely convert and tune a spectrum makes them ideal for LCD displays. Previous LCD displays can waste energy converting red-green poor, blue-yellow rich white light into a more balanced lighting. By using QDs, only the necessary colors for ideal images are contained in the screen. The result is a screen that is brighter, clearer, and more energy-efficient. Researchers are also working on the use of quantum dots in displays for applications ranging from your cell phone to large screen televisions that would consume less power than current displays. By placing different size quantum dots in each pixel of a display screen, the red, green, and blue colors used to generate the full spectrum of colors would be available. The book Quantum Dots - Theory and Applications covers some new research results in the field of fundamental excitations, decoherence, charge states, epitaxial techniques and photoluminescence experiments related to devices made with quantum dots also includes numerous applications of quantum dots.
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 Luminescence Spectroscopy of Semiconductors written by Ivan Pelant and published by OUP Oxford. This book was released on 2012-02-02 with total page 557 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reviews up-to-date ideas of how the luminescence radiation in semiconductors originates and how to analyze it experimentally. The book fills a gap between general textbooks on optical properties of solids and specialized monographs on luminescence. It is unique in its coherent treatment of the phenomenon of luminescence from the very introductory definitions, from light emission in bulk crystalline and amorphous materials to the advanced chapters that deal with semiconductor nano objects, including spectroscopy of individual nanocrystals. The theory of radiative recombination channels in semiconductors is considered on a level of intuitive physical understanding rather than rigorous quantum mechanical treatment. The book is based on teaching and written in the style of a graduate text with plenty of tutorial material, illustrations, and problem sets at chapter ends. It is designed predominantly for students in physics, optics, optoelectronics and materials science.
Download or read book Quantum Dot Photodetectors written by Xin Tong and published by Springer Nature. This book was released on 2021-09-17 with total page 319 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents a comprehensive overview of state-of-the-art quantum dot photodetectors, including device fabrication technologies, optical engineering/manipulation strategies, and emerging photodetectors with building blocks of novel quantum dots (e.g. perovskite) as well as their hybrid structured (e.g. 0D/2D) materials. Semiconductor quantum dots have attracted much attention due to their unique quantum confinement effect, which allows for the facile tuning of optical properties that are promising for next-generation optoelectronic applications. Among these remarkable properties are large absorption coefficient, high photosensitivity, and tunable optical spectrum from ultraviolet/visible to infrared region, all of which are very attractive and favorable for photodetection applications. The book covers both fundamental and frontier research in order to stimulate readers' interests in developing novel ideas for semiconductor photodetectors at the center of future developments in materials science, nanofabrication technology and device commercialization. The book provides a knowledge sharing platform and can be used as a reference for researchers working in the fields of photonics, materials science, and nanodevices.
Download or read book Transition Metal Doped Semiconductor Quantum Dot Alloys written by Khalid M. Hanif and published by . This book was released on 2004 with total page 472 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Selected Papers on Semiconductor Quantum Dots written by Frank W. Wise and published by SPIE-International Society for Optical Engineering. This book was released on 2005 with total page 408 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconductor quantum dots, also known as nanocrystals, are structures with electronic and optical properties that can be engineered through the size of the structure, not just the composition. Quantum confinement of charge carriers leads to a wide range of intriguing physical and chemical phenomena, and is a new degree of freedom in material design. Semiconductor quantum dots have potential for applications ranging from optoelectronic devices to biological imaging. The papers selected for this volume treat the fundamental properties of semiconductor quantum dots and form a significant part of the foundation on which the current field of nanoscience research is built.
Download or read book The Interplay of Size and Site Dependence of Magnetic Properties of Diluted Magnetic Semiconductor Quantum Dots written by Weiwei Zheng and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: This dissertation studies the size- and site-dependent optical and magnetic properties of II-VI quantum dots (QDs). The first chapter provides a theoretical background used to analyze the data and the properties expected for diluted magnetic semiconductor materials at the nanoscale. The second chapter probes the size-dependent magnetic properties for Mn doped CdSe QDs. The Curie-Weiss law plots show significant size-dependent carrier concentration in the QDs. The carriers inside the small QDs can mediate the Mn(II)-Mn(II) ferromagnetic interaction by the RKKY model, which helps explain reasons for the observation of a superparamagnetism (SPM) in small Mn-CdSe QDs. The third chapter involves high frequency EPR analysis of possible dopant (Mn(II) ions) sites in CdSe lattice. Surface doped Mn-CdSe QDs and stochastically doped Mn-CdSe QDs were successfully made by traditional thermal decomposition of cluster and microwave irradiation. Two sets of hyperfine splitting were observed for stochastically doped Mn-CdSe QDs from EPR spectra and the ratio of the signal has liner relationship with the surface to volume ratio of QDs. One set of hyperfine splitting can be removed by surface acid treatment enabled us to identify the Mn(II) sites on the surface or core position of Mn-CdSe QDs. The fourth chapter is a study of chromium incorporation in ZnSe QDs by single cubic source precursor method. The formation of ZnCr2Se4 spinel structure was approved by XANES, and 4A2g to 4T2g transition of Cr (III) ion in absorption spectra.
