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 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 Synthesis and Optimization of Quantum Dot based Technologies written by Toshia Lynn Wrenn and published by . This book was released on 2015 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Bandstructure Engineering of Indium Arsenide Quantum Dots in Gallium Arsenide Antimonide Barriers for Photovoltaic Applications written by Jonathan Boyle and published by ProQuest. This book was released on 2008 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: Increasing the efficiency of solar cell technology is one of the current research aims being under taken in order to help supply growing global energy demands. The research presented in this thesis contributes to the current materials hunt for suitable candidates for an Intermediate Band Solar Cell (IBSC). A background on other "third generation" photovoltaic concepts along with details about the IBSC concept is also presented.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 702 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis and Characterization of Infrared Quantum Dots written by Daniel Kelly Harris and published by . This book was released on 2014 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on the development of synthetic methods to create application ready quantum dots (QDs) in the infrared for biological imaging and optoelectronic devices. I concentrated primarily on controlling the size and size distribution of indium arsenide and cadmium arsenide QDs. In the nanocrystal community, classical nucleation and growth is often invoked to explain size focusing. However, this model lacks predictive power and contradicts what is known about the chemistry of QD growth. I try to relate my experimental approach and my conclusions to our understanding of the mechanism of particle growth. This approach led me to explore the role of precursor conversion rate in the growth of III-V QDs and to develop a continuous injection synthesis method that I used to make both III-V and cadmium arsenide QDs. Cadmium arsenide (Cd 3As 2 ) is a narrow gap semiconductor that can form QDs with tunable emission between 530nm and 2000nm. I developed a synthetic strategy to precisely control the size of Cd3As 2 QDs while maintaining a narrow size distribution. Continuous precursor injection was used to drive growth and suppress size broadening. The quantum yields of Cd3As 2 QDs produced using this method ranged as high as 80%, and their emission is tunable over a broad range with narrow linewidths. However, they were found to be unstable in ambient conditions. Nevertheless, by processing in inert conditions we were able to make a crude photodetector that demonstrates that Cd3As 2 QDs are sufficiently stable for use in optoelectronic devices. Although growth of a Cd3 P2 shell provided enough added stability to observe emission after ligand exchange into water, these core-shell structures do not seem to be robust enough for biological applications. Indium arsenide (InAs) QDs are more easily stabilized with a core-shell structure. However, the spectral linewidths are broad and existing synthetic techniques produce only small particles with limited spectral tunability. Models predicted that decreasing precursor reactivity would produce larger, more monodisperse particles. Therefore, I chemically modified the group-V precursor to reduce reactivity. I made a library of group-V precursors, and I developed a framework for comparing the QDs that they produced and measuring the kinetics of precursor conversion and particle growth. Although we successfully reduced precursor reactivity, we found that the effect on particle size was minimal and that the least reactive precursors produced particles with inferior size distributions. To find another way to try to improve III-V synthesis, I adapted the continuous injection method developed for making Cd3As 2. Using this strategy, I was able to produce InAs QDs with broadly tunable size and narrow spectral features. However, continuous injection ceases to drive particle growth beyond about 5nm in diameter. We examined why particle growth stops, and proposed a strategy to prolong growth and size focusing. Ultimately, the continuous injection technique allowed us to produce InAs QDs with infrared emission and narrow spectral features that were ideally suited for producing QDs optimized for deep tissue imaging in mice. By adding a shell of CdSe, CdS, or ZnSe, the quantum yield and stability were enhanced. These emitters allowed us to see biodistribution and biological processes occurring inside live mice. Although we found that precursor chemistry did not affect particle growth to the degree we hoped, we were able to produce application ready QDs via a continuous injection procedure. Continuous injection synthesis of QDs is a precise way to tune QD size while maintaining narrow size distributions. We have used this technique to produce QDs with the specifications required for high impact applications.

Download or read book Self Assembled Quantum Dots written by Zhiming M Wang and published by Springer Science & Business Media. This book was released on 2007-11-29 with total page 470 pages. Available in PDF, EPUB and Kindle. Book excerpt: This multidisciplinary book provides up-to-date coverage of carrier and spin dynamics and energy transfer and structural interaction among nanostructures. Coverage also includes current device applications such as quantum dot lasers and detectors, as well as future applications to quantum information processing. The book will serve as a reference for anyone working with or planning to work with quantum dots.

Download or read book Material Characterization and Process Development for Indium arsenide written by Rohan K. Bambery and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Efforts to push the performance of transistors for millimeter-wave and microwave applications have borne fruit through device size scaling and the use of novel material systems. III-V semiconductors and their alloys hold a distinct advantage over silicon because they have much higher electron mobility which is a prerequisite for high frequency operation. InGaAs/InP pseudomorphic heterojunction bipolar transistors (HBTs) have demonstrated fT of 765 GHz at room temperature and InP based high electron mobility transistors (HEMTs) have demonstrated fMax of 1.2 THz. The 6.1 A lattice family of InAs, GaSb, AlSb covers a wide variety of band gaps and is an attractive future material system for high speed device development. Extremely high electron mobilities ~ 30,000 cm^2 V^-1s^-1 have been achieved in modulation doped InAs-AlSb structures. The work described in this thesis involves material characterization and process development for HEMT fabrication on this material system.

Download or read book Indium Arsenide gallium Arsenide Antimonide Quantum Dots and Their Applications in Intermediate Band Solar Cells written by Anthony James Meleco and published by . This book was released on 2016 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Advanced Energy Materials written by Ashutosh Tiwari and published by John Wiley & Sons. This book was released on 2014-02-12 with total page 416 pages. Available in PDF, EPUB and Kindle. Book excerpt: An essential resource for scientists designing new energy materials for the vast landscape of solar energy conversion as well as materials processing and characterization Based on the new and fundamental research on novel energy materials with tailor-made photonic properties, the role of materials engineering has been to provide much needed support in the development of photovoltaic devices. Advanced Energy Materials offers a unique, state-of-the-art look at the new world of novel energy materials science, shedding light on the subject’s vast multi-disciplinary approach The book focuses particularly on photovoltaics, efficient light sources, fuel cells, energy-saving technologies, energy storage technologies, nanostructured materials as well as innovating materials and techniques for future nanoscale electronics. Pathways to future development are also discussed. Critical, cutting-edge subjects are addressed, including: Non-imaging focusing heliostat; state-of-the-art of nanostructures Metal oxide semiconductors and their nanocomposites Superionic solids; polymer nanocomposites; solid electrolytes; advanced electronics Electronic and optical properties of lead sulfide High-electron mobility transistors and light-emitting diodes Anti-ferroelectric liquid crystals; PEEK membrane for fuel cells Advanced phosphors for energy-efficient lighting Molecular computation photovoltaics and photocatalysts Photovoltaic device technology and non-conventional energy applications Readership The book is written for a large and broad readership including researchers and university graduate students from diverse backgrounds such as chemistry, materials science, physics, and engineering working in the fields of nanotechnology, photovoltaic device technology, and non-conventional energy.

Download or read book Silicon Heterojunction Solar Cells written by W.R. Fahrner and published by Trans Tech Publications Ltd. This book was released on 2006-08-15 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: The world of today must face up to two contradictory energy problems: on the one hand, there is the sharply growing consumer demand in countries such as China and India. On the other hand, natural resources are dwindling. Moreover, many of those countries which still possess substantial gas and oil supplies are politically unstable. As a result, renewable natural energy sources have received great attention. Among these, solar-cell technology is one of the most promising candidates. However, there still remains the problem of the manufacturing costs of such cells. Many attempts have been made to reduce the production costs of “conventional” solar cells (manufactured from monocrystalline silicon using diffusion methods) by instead using cheaper grades of silicon, and simpler pn-junction fabrication. That is the ‘hero’ of this book; the heterojunction solar cell.

Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2002 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 Preparation and Characterization of Indium Galium Arsenide Homojunction Solar Cell by Liquid Phase Epitaxy written by Willy Dirgahayu Notohamiprodjo and published by . This book was released on 1990 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Synthesis Optimization and Characterization of Carbon Quantum Dots written by Vibha Deshpande and published by . This book was released on 2016 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Quantum dots are Nano-sized structures of semiconductors with unique optical properties that make them a very valuable tool in a wide range of interesting and important applications. Quantum dots can be designed to emit a particular colored light by altering their size; they are long-lived and fluoresce brightly. Consequently, they have been used extensively in biological imaging studies, where they have facilitated the observation of detailed biological processes at the molecular level. The thesis work focuses on understanding the fundamental electronic properties of low dimensional material and their Biological applications. Carbon based Quantum Dots is the main subject in our project due to their biocompatibility and novel optical properties. Here we studied the structural, luminescence, biological properties and applications of carbon based different sizes of quantum dots. Our main goal lied in the formulation of highly florescent, broad range pH and ionic-stable N/S-doped Carbon based Quantum Dots for the purpose of determining or studying Inter and intra Cellular Functions and Imaging Live Cells. The Studies also include the effect of doping carbon based Quantum Dots. Our interest also lies in using scanning probe microscopy to investigate these quantum dots. Since the carbon element is the basis of all biological materials, full carbon nanomaterial’s have a lower toxicity compared with other nanomaterial’s; simultaneously, the particle size of CQDs is smaller and thus more convenient to enter the cell in vivo, which makes CQDs having great potential applications in the biological fields. In addition, the surface of CQDs contains a lot of functional groups, so that it can be modified with organic, inorganic, polymer, and other substances endowing different functional properties."--

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.