Download or read book Study of InAs Quantum Dots on GaAsSb for Intermediate Band Solar Cells written by Keun-Yong Ban and published by . This book was released on 2010 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Epitaxial Growth of High Quality InAs GaAsSb Quantum Dots for Solar Cells written by Yeongho Kim and published by . This book was released on 2015 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: The development of high efficiency III-V solar cells is needed to meet the demands of a promising renewable energy source. Intermediate band solar cells (IBSCs) using semiconductor quantum dots (QDs) have been proposed to exceed the Shockley-Queisser efficiency limit [1]. The introduction of an IB in the forbidden gap of host material generates two additional carrier transitions for sub-bandgap photon absorption, leading to increased photocurrent of IBSCs while simultaneously allowing an open-circuit voltage of the highest band gap. To realize a high efficiency IBSC, QD structures should have high crystal quality and optimized electronic properties. This dissertation focuses on the investigation and optimization of the structural and optical properties of InAs/GaAsSb QDs and the development of InAs/GaAsSb QD-based IBSCs.In the present dissertation, the interband optical transition and carrier lifetime of InAs/GaAsSb QDs with different silicon delta-doping densities have been first studied by time-integrated and time-resolved photoluminescence (PL). It is found that an optimized silicon delta-doping density in the QDs enables to fill the QD electronic states with electrons for sub-bandgap photon absorption and to improve carrier lifetime of the QDs.After that, the crystal quality and QD morphology of single- and multi-stack InAs/GaAsSb QDs with different Sb compositions have been investigated by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The TEM studies reveal that QD morphology of single-stack QDs is affected by Sb composition due to strain reducing effect of Sb incorporation. The XRD studies confirm that the increase of Sb composition increases the lattice mismatch between GaAs matrix and GaAsSb spacers, resulting in increase of the strain relaxation in GaAsSb of the multi-stack QDs. Furthermore, the increase of Sb composition causes a PL redshift and increases carrier lifetime of QDs.Finally, the spacer layer thickness of multi-stack InAs/GaAsSb QDs is optimized for the growth of InAs/GaAsSb QD solar cells (QDSCs). The InAs/GaAsSb QDSCs with GaP strain compensating layer are grown and their device performances are characterized. The increase of GaP coverage is beneficial to improve the conversion efficiency of the QDSCs. However, the conversion efficiency is reduced when using a relatively large GaP coverage.

Download or read book Indium Gallium arsenide Quantum Dot Materials for Solar Cell Applications written by Anup Pancholi and published by ProQuest. This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The last few years have seen rapid advances in nanoscience and nanotechnology, allowing unprecedented manipulation of nanostructures controlling solar energy capture, conversion, and storage. Quantum confined nanostructures, such as quantum wells (QWs) and quantum dots (QDs) have been projected as potential candidates for the implementation of some high efficiency photovoltaic device concepts, including the intermediate band solar cell (IBSC). In this dissertation research, we investigated multiple inter-related themes, with the main objective of providing a deeper understanding of the physical and optical properties of QD structures relevant to the IBSC concept. These themes are: (i) Quantum engineering and control of energy levels in QDs, via a detailed study of the electronic coupling in multilayer QD structures; (ii) Controlled synthesis of well-organized, good quality, high volume density, and uniform-size QD arrays, in order to maximize the absorption efficiency and to ensure the coupling between the dots and the formation of the minibands; and (iii) Characterization of carrier dynamics and development of techniques to enhance the charge transport and efficient light harvesting. A major issue in a QD-based IBSC is the occurrence of charge trapping, followed by recombination in the dots, which results in fewer carriers being collected and hence low quantum efficiency. In order to collect most of the light-generated carriers, long radiative lifetimes, higher mobilities, and a lower probability of non-radiative recombination events in the solar cell would be desirable. QD size-dependent radiative lifetime and electronic coupling in multilayer QD structures were studied using photoluminescence (PL) and time-resolved photoluminescence (TRPL). For the uncoupled QD structures with thick barriers between the adjacent QD layers, the radiative lifetime was found to increase with the QD size, which was attributed to increased oscillator strength in smaller size dots. On the other hand, in the sample with thin barrier and electronically coupled QDs, the radiative lifetime increases and later decreases with the dot size. This is due to the enhancement of the oscillator strength in the larger size, coherently coupled QDs. In order to improve the quality of multi-layer QD structures, strain compensated barriers were introduced between the QD layers grown on off-oriented GaAs (311)B substrate. The QD shape anisotropy resulted from the growth on off-oriented substrate was studied using polarization-dependent PL measurements both on the surface and the edge of the samples. The transverse electric mode of the edge-emitted PL showed about 5° deviation from the sample surface for the dots grown on (311)B GaAs, which was attributed to the tilted vertical alignment and the shape asymmetry of dots resulted from the substrate orientation. Significant structural quality improvements were attained by introducing strain compensated barriers, i.e., reduction of misfit dislocations and uniform dot size formation. Longer lifetime (~1 ns) and enhanced PL intensity at room temperature were obtained, compared to those in conventional multilayer (In, Ga)As/GaAs QD structures. A significant increase in the open circuit voltage (V oc) was observed for the solar cell devices fabricated with the strain compensated structures. A major issue in a QD IBSC is the occurrence of charge trapping, followed by recombination in the dots, which results in fewer carriers being collected, and hence low quantum efficiency. We proposed and studied a novel structure, in which InAs QDs were sandwiched between GaAsSb (12% Sb) strain-reducing layers (SRLs) with various thicknesses. Both short (~1 ns) and long (~4-6 ns) radiative lifetimes were measured in the dots and were attributed to type-I and type-II transitions, respectively, which were induced by the band alignment modifications at the QD/barrier interface in the structures analyzed, due to the quantum confinement effect resulting from different GaAsSb barrier thicknesses. Based on our findings, a structure with type-II QD/barrier interface with relatively long radiative recombination lifetime may be a viable candidate in designing IBSC.

Download or read book Growth and Characterization of Self assembled Quantum Dots for Intermediate Band Solar Cells written by Meng Sun and published by . This book was released on 2013 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this study, Molecular Beam Epitaxy technology is presented in detail and several powerful characterization techniques such as XRD, AFM, TEM, PL are also reviewed. SAQDs are discussed to be applied in IBSCs application due to the formation of intermediate band which helps to absorb sub-band gap photons. We investigate how the structural and optical properties of InAs self-assembled quantum dots buried in AlAs0.56Sb0.44 barriers can be controlled through the use of thin GaAs1xSbx cladding layers. Structural and optical properties of the SAQDs are studied, and the characteristics we demonstrate for this quantum dot system show great potential for application in intermediate band solar cells.

Download or read book Quantum Dots for Intermediate Band in Solar Cells written by Shadi Dashmiz and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Structural Optical and Spectral Behaviour of InAs based Quantum Dot Heterostructures written by Saumya Sengupta and published by Springer. This book was released on 2017-08-04 with total page 77 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book explores the effects of growth pause or ripening time on the properties of quantum dots(QDs). It covers the effects of post-growth rapid thermal annealing (RTA) treatment on properties of single layer QDs. The effects of post-growth rapid thermal annealing (RTA) treatment on properties of single layer QDs are discussed. The book offers insight into InAs/GaAs bilayer QD heterostructures with very thin spacer layers and discusses minimum spacer thickness required to grow electronically coupled bilayer QD heterostructures. These techniques make bilayer QD heterostructures a better choice over the single layer and uncoupled multilayer QD heterostructure. Finally, the book discusses sub-monolayer (SML) growth technique to grow QDs. This recent technique has been proven to improve the device performance significantly. The contents of this monograph will prove useful to researchers and professionals alike.

Download or read book Self Assembled InGaAs GaAs Quantum Dots written by and published by Academic Press. This book was released on 1999-03-29 with total page 385 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume is concerned with the crystal growth, optical properties, and optical device application of the self-formed quantum dot, which is one of the major current subjects in the semiconductor research field.The atom-like density of states in quantum dots is expected to drastically improve semiconductor laser performance, and to develop new optical devices. However, since the first theoretical prediction for its great possibilities was presented in 1982, due to the difficulty of their fabrication process. Recently, the advent of self-organized quantum dots has made it possible to apply the results in important optical devices, and further progress is expected in the near future.The authors, working for Fujitsu Laboratories, are leading this quantum-dot research field. In this volume, they describe the state of the art in the entire field, with particular emphasis on practical applications.

Download or read book Quantum Dot Enhanced Epitaxial Lift off Solar Cells written by Mitchell F. Bennett and published by . This book was released on 2013 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Embedded nanostructures such as quantum dots (QDs) have been studied for many applications in solar cells including enhanced mini-band absorption in intermediate-band solar cells and current matching in multi junction cells. The major drawbacks of using such techniques to decrease intrinsic solar cell loss mechanisms are twofold: first, it is difficult to maintain partially populated states using QDs due to a quick thermal extraction of carriers; second, QDs have a weak absorption which necessitates a near-perfect control of QD growth mechanisms to carefully ensure a balance between dot size and density. One avenue for improving absorption into QDs is to utilize a thin cell with a back surface reflector in order to increase the effective optical path length (OPL) of light through the QD region, which has the potential to increase absorption into QD states. One method for the processing of thin solar cells that has been experimentally demonstrated on large 4-6" wafers is epitaxial lift-off, which takes advantage of an inverted growth and a wet chemical etch of a sacrificial release layer to remove the substrate. In this thesis, 0.25 cm2 InAs/GaAs QD cells were grown on 4" wafers, fabricated, and processed by epitaxial lift off, creating thin and flexible devices. Materials and optical characterization techniques such as atomic force microscopy and photoluminescence were used on test structures prior to and following ELO, and analysis indicated that QD optical coherence and material quality after ELO processing were preserved, although non-uniform. This was concluded to be caused by the radial thermal profile of the growth reactor, through which spatial dependence led to local variations in QD quality and size across the 4" wafer, indicative of the high temperature sensitivity of QDs. Transmission electron microscopy measurements were used to investigate defects and dislocations throughout the QD device structure that would impact performance, and showed a higher concentration of defects in regions of the wafer subject to a higher temperature during growth. A similar pattern of radial dependence was observed in solar cell devices by electrical characterization. Current-voltage measurements under one-sun AM0 illumination were taken on several cells around the wafer, showing a statistical variation in solar cell device metrics dependent on wafer position. Spectral responsivity measurements show an established cavity mode pattern in sub-host bandgap wavelengths, which is discussed as an enhancement due to the thinning of the device. Integrated external quantum efficiency shows a QD contribution to the short circuit current density of 0.23 mA/cm2. In addition to optical, materials, and electrical characterization, QD and baseline ELO devices were exposed to alpha radiation to gauge the effects of a harmful environment on cell performance. The QD device exhibited a remaining factor increase of 2 % (absolute) in conversion efficiency over the baseline device at an end of life alpha particle fluence of 5x109[alpha]/cm2/s. In addition, linear temperature coefficients for solar cell figures of merit were extracted as a function of increasing [alpha] fluence. At a fluence of 5x108[alpha]/cm2/s, the QD device showed an efficiency temperature coefficient 0.2 %/°C higher (absolute) than the baseline, indicating that the inclusion of QDs could improve the radiation and temperature tolerance of solar cell devices used for space applications."--Abstract.

Download or read book ICICCT 2019 System Reliability Quality Control Safety Maintenance and Management written by Vinit Kumar Gunjan and published by Springer. This book was released on 2019-06-27 with total page 874 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book discusses reliability applications for power systems, renewable energy and smart grids and highlights trends in reliable communication, fault-tolerant systems, VLSI system design and embedded systems. Further, it includes chapters on software reliability and other computer engineering and software management-related disciplines, and also examines areas such as big data analytics and ubiquitous computing. Outlining novel, innovative concepts in applied areas of reliability in electrical, electronics and computer engineering disciplines, it is a valuable resource for researchers and practitioners of reliability theory in circuit-based engineering domains.

Download or read book Nanoscale Applications for Information and Energy Systems written by Anatoli Korkin and published by Springer Science & Business Media. This book was released on 2012-10-28 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanoscale Applications for Information and Energy Systems presents nanotechnology fundamentals and applications in the key research areas of information technology (electronics and photonics) and alternative (solar) energy: plasmonics, photovoltaics, transparent conducting electrodes, silicon electroplating, and resistive switching. The three major technology areas – electronics, photonics, and solar energy – are linked on the basis of similar applications of nanostructured materials in research and development. By bridging the materials physics and chemistry at the atomic scale with device and system design, integration, and performance requirements, tutorial chapters from worldwide leaders in the field provide a coherent picture of theoretical and experimental research efforts and technology development in these highly interdisciplinary areas.

Download or read book Advanced Concepts in Photovoltaics written by Arthur J. Nozik and published by Royal Society of Chemistry. This book was released on 2014-07-10 with total page 631 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photovoltaic systems enable the sun’s energy to be converted directly into electricity using semiconductor solar cells. The ultimate goal of photovoltaic research and development is to reduce the cost of solar power to reach or even become lower than the cost of electricity generated from fossil and nuclear fuels. The power conversion efficiency and the cost per unit area of the phototvoltaic system are critical factors that determine the cost of photovoltaic electricity. Until recently, the power conversion efficiency of single-junction photovoltaic cells has been limited to approximately 33% - the so-called Shockley-Queisser limit. This book presents the latest developments in photovoltaics which seek to either reach or surpass the Shockley-Queisser limit, and to lower the cell cost per unit area. Progress toward this ultimate goal is presented for the three generations of photovoltaic cells: the 1st generation based on crystalline silicon semiconductors; the 2nd generation based on thin film silicon, compound semiconductors, amorphous silicon, and various mesoscopic structures; and the 3rd generation based on the unique properties of nanoscale materials, new inorganic and organic photoconversion materials, highly efficient multi-junction cells with low cost solar concentration, and novel photovoltaic processes. The extent to which photovoltaic materials and processes can meet the expectations of efficient and cost effective solar energy conversion to electricity is discussed. Written by an international team of expert contributors, and with researchers in academia, national research laboratories, and industry in mind, this book is a comprehensive guide to recent progress in photovoltaics and essential for any library or laboratory in the field.

Download or read book Quantum Dot Heterojunction Solar Cells written by Rachelle Ihly and published by . This book was released on 2014 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis explores the understanding of the chemistry and physics of colloidal quantum dots for practical solar energy photoconversion. Solar cell devices that make use of PbS quantum dots generally rely on constant and unchanged optical properties such that band gap energies remain tuned within the device. The design and development of unique experiments to ascertain mechanisms of optical band gap shifts occurring in PbS quantum dot thin-films exposed to air are discussed. The systematic study of the absorption properties of PbS quantum dot films exposed to air, heat, and UV illumination as a function of quantum dot size has been described. A method to improve the air-stability of films with atomic layer deposition of alumina is demonstrated. Encapsulation of quantum dot films using a protective layer of alumina results in quantum dot solids that maintain tuned absorption for 1000 hours. This thesis focuses on the use of atomic force microscopy and electrical variants thereof to study the physical and electrical characteristics of quantum dot arrays. These types of studies have broad implications in understanding charge transport mechanisms and solar cell device operation, with a particular emphasis on quantum dot transistors and solar cells. Imaging the channel potential of a PbSe quantum dot thin-film in a transistor showed a uniform distribution of charge coinciding with the transistor current voltage characteristics. In a second study, solar cell device operation of ZnO/PbS heterojunction solar cells was investigated by scanning active cross-sections with Kelvin probe microscopy as a function of applied bias, illumination and device architecture. This technique directly provides operating potential and electric field profiles to characterize drift and diffusion currents occurring in the device. SKPM established a field-free region occurring in the quantum dot layer, indicative of diffusion-limited transport. These results provide the path to optimization of future architectures that may employ drift-based transport in the quantum dot layer for enhanced charge extraction and power conversion efficiency.

Download or read book Optimization and Characterization of Indium Arsenide Quantum Dots for Application in III V Material Solar Cells written by Adam M. Podell and published by . This book was released on 2014 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: "In this work, InAs quantum dots grown by organometallic vapor-phase epitaxy (OMVPE) are investigated for application in III-V material solar cells. The first focus is on the optimization of growth parameters to produce high densities of uniform defect-free quantum dots via growth on 2" vicinal GaAs substrates. Parameters studied are InAs coverage, V/III ratio and growth rate. QDs are grown by the Stranski-Krastanov (SK) growth mode on (100) GaAs substrates misoriented toward (110) or (111) planes with various degrees of misorientation from 0° to 6°. Atomic force microscopy results indicated that as misorientation angle increased toward (110), critical thickness for quantum dot formation increased with [theta][subscript c] = 1.8 ML, 1.9 ML and 2.0 ML corresponding to 0°, 2° and 6°, respectively. Results for quantum dots grown on (111) misoriented substrates indicated, on average, that higher densities of quantum dots were achieved, compared with similar growths on substrates misoriented toward (110). Most notably, a stable average number density of 8 x 1010 cm−2 was observed over a range of growth rates of 0.1 ML/s - 0.4 ML/s on (111) misoriented substrates compared with a decreasing number density as low as 2.85 x 1010 cm−2 corresponding to a growth rate of 0.4 ML/s grown on (110) misoriented substrates. p-i-n solar cell devices with a 10-layer quantum dot superlattice imbedded in the i-region were also grown on (100) GaAs substrates misoriented 0°, 2° and 6° toward (110) as well as a set of devices grown on substrates misoriented toward (111). Device results showed a 1.0mA/cm2 enhancement to the short-circuit current for a 2° misoriented device with 2.2 ML InAs coverage per quantum dot layer. Spectral response measurements were performed and integrated spectral response showed sub-GaAs bandgap short-circuit contribution which increased with increasing InAs coverage in the quantum dot layers from 0.04mA/cm2/ML and 0.19mA/cm2/ML corresponding to 0°, 2° and 6° misorientation, respectively.""--Abstract.

Download or read book Basic Research of Self Organized Quantum Dots and Their Potential In Solar Cells and Novel Devices Applications Phase 4 written by and published by . This book was released on 2006 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the research output from our AOARD-supported work on basic investigation of self-assembled quantum dots and their potential applications during 2006. The research project is the fourth year of AOARD-support following the previous ones in 2003 2004 and 2005. During the past year, 6 international journal publications on self-assembled quantum dots and quantum dot molecules, heterostructure solar cells and quantum dot solar cells were published. There were technical papers on different growth techniques for different patterns of quantum dot molecules, e.g. bi-quantum dot molecules, long chain quantum dot molecules, quantum dot rings presented at 14th International Conference on Molecular Beam Epitaxy (MBE 2006), 32nd International Conference on Micro-and Nano- Engineering (MNE 2006), Electronic Material Conference (EMC 2006) and ECTI-CON 2006. Three papers on quantum dot molecule solar cells and their potential applications at high concentrated sunlight were also presented at major international solar cell conferences, i.e. 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4), 21st European PVSEC and at MRS (Material Research Society) Fall Meeting 2006. All our journal and technical papers (17 in total) acknowledge financial supports from AOARD and Thailand Research Fund (TRF). Research work on quantum dot molecules based on InAs and InP materials will be investigated and their applications for high efficiency solar cells will be presented in the upcoming 2nd IEEE-NEMs (Nano/Micro Engineered and Molecular Systems) in 2007. Challenge of 30 % up efficiency quantum dot molecular solar cells will be our target of our research in 2007 and 2008.

Download or read book CMOSET 2013 Vol 6 Devices Energy and Sensors Track written by CMOS Emerging Technologies Research and published by CMOS Emerging Technologies. This book was released on 2014-06-23 with total page 451 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presentation slides from the 2013 CMOS Emerging Technologies Research conference in Whistler, Canada.

Download or read book Electronic and Optical Properties of InAs GaAs Semiconductor Quantum Dots written by Mark Thomas Crowley and published by . This book was released on 2010 with total page 191 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents a theoretical study of the 1.3mm InAs/GaAs semiconductor quantum dot (QD) material system. A detailed 8-band k.P formalism accounting for all strain effects is used to calculate realistic distributions of dot carrier levels for typical 1.3mm InAs/GaAs dot structures as well as computing the optical transition strengths between these carrier states. The observed weak variation of the threshold radiative current density of 1.3mm InAs/GaAs QD lasers with temperature is shown to result from the much weaker optical matrix element of the excited dot states relative to the ground state (GS) transition. The observed sharp increase of the nonradiative component of the threshold current density around room temperature is attributed to Auger recombination. It is concluded that temperature-dependent loss mechanisms remain as significant in 1.3mm QD lasers as in conventional 1.3mm devices. The observation of a finite GS transverse magnetic absorption is attributed to transitions between GS electrons and low-lying excited hole states which possess a significant light-hole component of the correct symmetry to recombine with the GS electrons. It is shown that this absorption line is enhanced for dots having a small base to height aspect ratio whereas for dots with large aspect ratio it is effectively switched off. In addition, the absorption spectrum of GS electrons is found to consist of two distinct absorption lines. The lower energy of these originates from recombination between GS electrons and GS holes. The second, higher energy peak, arises primarily due to recombination between GS electrons and with holes containing GS light-hole character. Finally, two colour phase dynamics at 1.3mm are investigated. It is shown that InAs/GaAs QD SOAs retain significant promise for high speed optical switches based on cross phase modulation.

Download or read book Metalorganic Vapor Phase Epitaxy MOVPE written by Stuart Irvine and published by John Wiley & Sons. This book was released on 2019-10-07 with total page 582 pages. Available in PDF, EPUB and Kindle. Book excerpt: Systematically discusses the growth method, material properties, and applications for key semiconductor materials MOVPE is a chemical vapor deposition technique that produces single or polycrystalline thin films. As one of the key epitaxial growth technologies, it produces layers that form the basis of many optoelectronic components including mobile phone components (GaAs), semiconductor lasers and LEDs (III-Vs, nitrides), optical communications (oxides), infrared detectors, photovoltaics (II-IV materials), etc. Featuring contributions by an international group of academics and industrialists, this book looks at the fundamentals of MOVPE and the key areas of equipment/safety, precursor chemicals, and growth monitoring. It covers the most important materials from III-V and II-VI compounds to quantum dots and nanowires, including sulfides and selenides and oxides/ceramics. Sections in every chapter of Metalorganic Vapor Phase Epitaxy (MOVPE): Growth, Materials Properties and Applications cover the growth of the particular materials system, the properties of the resultant material, and its applications. The book offers information on arsenides, phosphides, and antimonides; nitrides; lattice-mismatched growth; CdTe, MCT (mercury cadmium telluride); ZnO and related materials; equipment and safety; and more. It also offers a chapter that looks at the future of the technique. Covers, in order, the growth method, material properties, and applications for each material Includes chapters on the fundamentals of MOVPE and the key areas of equipment/safety, precursor chemicals, and growth monitoring Looks at important materials such as III-V and II-VI compounds, quantum dots, and nanowires Provides topical and wide-ranging coverage from well-known authors in the field Part of the Materials for Electronic and Optoelectronic Applications series Metalorganic Vapor Phase Epitaxy (MOVPE): Growth, Materials Properties and Applications is an excellent book for graduate students, researchers in academia and industry, as well as specialist courses at undergraduate/postgraduate level in the area of epitaxial growth (MOVPE/ MOCVD/ MBE).