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Author: Lawrence William James
Publisher:
ISBN:
Category : Gallium arsenide
Languages : en
Pages : 144
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Book Description
Considerable interest has been shown in developing a practical photocathode using the GaAs-Cs system. It was felt that a thorough study of the photoemission from vacuum cleaved surfaces would eliminate the variable of surface preparation, and allow a detailed examination of the photoemission process in GaAs. In the process of this examination, new instrumentation allowing high resolution measurement of emitted electron energy distributions and their derivatives was developed, and played a critical role in making sufficient information available from experiment to allow the description of the photoemission process in terms of meaningful quantitative theories. In parallel with other laboratories, a process was developed for applying additional layers of oxygen and cesium to the surface, resulting in a lower vacuum level and an increased quantum efficiency. The report covers in detail the methods and results of the experimental work conducted, and the theories which have been developed to explain the experimental results. (Author).
Author: Lawrence William James
Publisher:
ISBN:
Category : Gallium arsenide
Languages : en
Pages : 144
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Book Description
Considerable interest has been shown in developing a practical photocathode using the GaAs-Cs system. It was felt that a thorough study of the photoemission from vacuum cleaved surfaces would eliminate the variable of surface preparation, and allow a detailed examination of the photoemission process in GaAs. In the process of this examination, new instrumentation allowing high resolution measurement of emitted electron energy distributions and their derivatives was developed, and played a critical role in making sufficient information available from experiment to allow the description of the photoemission process in terms of meaningful quantitative theories. In parallel with other laboratories, a process was developed for applying additional layers of oxygen and cesium to the surface, resulting in a lower vacuum level and an increased quantum efficiency. The report covers in detail the methods and results of the experimental work conducted, and the theories which have been developed to explain the experimental results. (Author).
Author: Ronald E. Warwick
Publisher:
ISBN:
Category : Gallium
Languages : en
Pages : 116
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Book Description
Author: James Francis Kearney
Publisher:
ISBN:
Category : Gallium compounds
Languages : en
Pages : 94
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Author: Stanford University. Stanford Electronics Laboratories
Publisher:
ISBN:
Category : Electrons
Languages : en
Pages : 328
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Book Description
Photoemission studies of the electronic energy band structures of gallium arsenide, gallium phosphide, and silicon are reported. The results of measurements of photoemissive yield and energy distributions for photoemitted electrons, as a function of the photon energy of the monochromatic light, are presented for both clean surfaces of GaAs, GaP and silicon, and those surfaces covered with a monolayer of cesium to lower the vacuum level. The structure features of the energy distribution curves for photoemitted electrons for GaAs, GaP, and Si are explained in detail in terms of direct interband transitions in the respective electronic energy band structures of the materials. The overall photoemission results for the three materials are shown to be quite similar, which reflects the basic similarity of their electronic band structures and optical spectra.
Author: Anup Pancholi
Publisher: ProQuest
ISBN: 9780549924562
Category : Gallium arsenide
Languages : en
Pages :
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Book Description
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.
Author: Georg Gaertner
Publisher: Springer Nature
ISBN: 3030472914
Category : Technology & Engineering
Languages : en
Pages : 609
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This book gives an overview of modern cathodes and electron emitters for vacuum tubes and vacuum electron devices in general. It covers the latest developments in field emission theory as well as new methods towards improving thermionic and cold cathodes. It addresses thermionic cathodes, such as oxide cathodes, impregnated and scandate cathodes, as well as photocathodes and field emitters – the latter comprising carbon nanotubes, graphene and Spindt-type emitter arrays. Despite the rise and fall of the once dominant types of vacuum tubes, such as radio valves and cathode ray tubes, cathodes are continually being improved upon as new applications with increased demands arise, for example in electron beam lithography, high-power and high-frequency microwave tubes, terahertz imaging and electron sources for accelerators. Written by 17 experts in the field, the book presents the latest developments in cathodes needed for these applications, discussing the state of the art and addressing future trends.
Author: Stanford University. Stanford Electronics Laboratories
Publisher:
ISBN:
Category :
Languages : en
Pages : 46
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Author:
Publisher:
ISBN:
Category : Science
Languages : en
Pages : 1296
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Author: Shigemasa Suga
Publisher: Springer Nature
ISBN: 3030640736
Category : Science
Languages : en
Pages : 511
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Book Description
This book presents photoelectron spectroscopy as a valuable method for studying the electronic structures of various solid materials in the bulk state, on surfaces, and at buried interfaces. This second edition introduces the advanced technique of high-resolution and high-efficiency spin- and momentum-resolved photoelectron spectroscopy using a novel momentum microscope, enabling high-precision measurements down to a length scale of some tens of nanometers. The book also deals with fundamental concepts and approaches to applying this and other complementary techniques, such as inverse photoemission, photoelectron diffraction, scanning tunneling spectroscopy, as well as photon spectroscopy based on (soft) x-ray absorption and resonance inelastic (soft) x-ray scattering. This book is the ideal tool to expand readers’ understanding of this marvelously versatile experimental method, as well as the electronic structures of metals and insulators.
Author: United States. Congress. House. Committee on Armed Services. Armed Services Investigating Subcommittee
Publisher:
ISBN:
Category : Research and development contracts
Languages : en
Pages : 286
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Book Description
