1,721,093 research outputs found
Kontrolle der Polarität und Dotierung in Aluminium Gallium Nitrid
Full text linkAlGaN basierte Laterale Polare Strukturen (LPS) können mit Hilfe der metallorganischen Gasphasenepitaxie gewachsen werden, indem man die c-Achse periodisch invertiert. Derartige Strukturen haben das Potential, um für Frequenzverdopplung von kohärentem Licht in das ultraviolette (UV) Spektralgebiet verwendet zu werden. Weitere Anwendungen liegen im Bereich lateraler p/n-Übergänge. Bezüglich ihrer Herstellung gibt es derzeit noch zwei wesentliche Herausforderungen, die gelöst werden müssen, um das volle Potential des Materialsystems für optoelektronische Bauelemente im UV ausnutzen zu können: (1) In AlGaN kann eine hohe Konzentration von intrinsischen und extrinsischen Störstellen zu einer reduzierten Quanteneffizienz von optischen Bauelementen führen. Dies ist besonders bei höheren Dotierungen der Fall, da es dort zur Selbstko mpensation des Dotanden kommen kann. (2) Werden III- und N-polare Domänen nebeneinanderliegend in einer LPS gewachsen, so wird in der Regel ein Schichtdickenunterschied zwischen den Domänen beobachtet. In der vorliegenden Arbeit wurden beide genannten Herausforderungen detailliert bearbeitet und gelöst. Im Fall von mit Si oder Mg dotiertem AlGaN führen hohe Störstellen-konzentrationen wie Stickstoffvakanzen, H oder O zu hohen Widerständen und einer niedrigen Beweglichkeit der freien Ladungsträger. Diese hohen Konzentrationen werden dadurch erklärt, dass im Bereich hoher Dotierungen die Formierungsenergien dieser S törstellen verringert werden, was zu einem erhöhten Einbau von Kompensatoren führt. Bestrahlt man AlGaN Filme während des Wachstums mit UV-Licht (entsprechend einer Anregungsenergie größer als die Bandlücke), führt dies zu einem verringertem Einbau von Störstellen. So kann z.B. in GaN:Mg eine stark reduzierte blaue Lumineszenz (2.8 eV) gemessen werden, was auf einen verringerten Einbau von Stickstoffvakanzen schließen lässt und zu einem geringerem elektrischen Widerstand führt. Des Weiteren wird im Rahmen dieser Arbeit gezeigt, dass das hier vorgestellte Modell zur Kontrolle des Einbaus von Defekten sowohl für n- als auch p-leitende Halbleiter verwendet werden kann. Die zweite Herausforderung des Schichtdickenunterschiedes der N- und III-polaren Domänen in LPS (2) wird in dieser Arbeit durch einen Oberflächenmassentransport zwischen den polaren GaN Domänen erklärt. Abhängig von der Wachstumsbedingung führt dieser Massentransport zu einem bevorzugten Wachstum jeweils einer polaren Domäne. Folglich konnten aber auch Bedingungen gefunden werden, in denen die Wachstumsrate der Domänen identisch ist und hoch qualitative AlGaN LPS mit Mikrometer großen Domäne n gewachsen werden. Abschließend wurden die Erkenntnisse aus (1) und (2) kombiniert und verbesserte elektrische und optische Eigenschaften lateraler p/n Übergänge nachgewiesen, wenn diese mit UV-Licht während des Wachstums bestrahlt wurden. Beides, sowohl die Störstellenkontrolle mittels UV-Bestrahlung als auch die Kontrolle der N- und III-polaren Domänen in LPS, wurde nie zuvor demonstriert und eröffnen einzigartige neue Möglichkeiten.AlGaN can be used for the fabrication of lateral polar structures (LPS) by a periodic inversion of the c-axis as achieved by a polarity control scheme during its growth by metal organic chemical vapor deposition (MOCVD). These structures can be used for second harmonic generation in the ultraviolet spectral region, as well as for lateral p/n-junctions. The two major challenges addressed in this work exist in the general implementation of the AlGaN technology and in the fabrication of AlGaN LPS, and both prevent the realization of AlGaN UV-emitters. These challenges are: (1) the presence of a high concentrations of native defects and extrinsic impurities in AlGaN that can reduce the efficiency of optoelectronic devices, especially in the case of high doping with Mg or Si, and (2) as typically observed, a growth rate difference that exists during the simultaneous growth of III- and N-polar domains adjacent to each other in a LPS.
In this dissertation, solutions to these two challenges are based on two novel and original approaches involving (1) Fermi-level point defect control schemes, and (2) mass transport control between polar domains. In approach (1), the control of point defects and reduction of compensations, VN, H or O are identified as the cause of high resistivity and low mobility in AlGaN due to their low formation energies at high Mg or Si doping concentrations. To confirm and quantify the Fermi-level point defect control scheme, above bandgap illumination during the growth of GaN was demonstrated to control the incorporation of these defects. Significant reductions in the point defect were achieved as evidenced by changes in their corresponding luminescence, for example, the blue luminescence at 2.8 eV (VN-related). Additionally, reduced resistivity and atomic concentrations, such as an order of magnitude lower H concentration, were observed. These studies confirm that the point defect management scheme developed in this work can control compensation in n-type as well as in p-type semiconductors.
In approach (2), mass transport control between polar domains, the surface mass transport between differently oriented domains was determined to be a function of the Ga supersaturation. Using Ga supersaturation as a control, a condition where identical growth rates for both polarities was obtained and high quality AlGaN LPS with domains in the micrometer scale could be fabricated. Furthermore, the first AlN LPS was grown and studied. Finally, the utility of these two new approaches was demonstrated by fabricating an AlGaN lateral p/n-junction that exhibited a marked decrease in compensation effects within each particular domain.
Both point defect control via above bandgap illumination, as well as the control of the growth rate difference of LPS, will have considerable impact on the field of III-V-nitrides as these novel approaches will potentially facilitate a new class of devices in the future
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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