1,720,973 research outputs found
Relaxed germanium epilayers on porous silicon buffers for low dislocation content Ge on Si virtual substrates
No full textWhile silicon represents the dominant material in the semiconductor industry, the continuous improvement in the performance of Si based devices is reaching its upper bound due to the approaching of insuperable physical limitations intrinsic to Si, which requires the introduction of new semiconductor materials and the development of new assembly techniques to guarantee the future performance improvement and reduction in fabrication costs. The integration of high-quality germanium epilayers on Si substrates has received great attention from the semiconductor community due to the chance to extend the range of performance offered by Si-based technology by taking advantage of both the superior properties of Ge such as a higher carrier mobility, a lattice constant close to that of GaAs which enables III-V epitaxy and a quasi-direct bandgap, and of the possibility of strain and bandgap engineering offered by the formation of a heterojunction.
To overcome the 4.2% lattice constant mismatch existing between Ge and Si which hamper the direct integration approach, this thesis investigates a novel technique for the realization of high-quality Ge on Si virtual substrates (VSs), consisting in the introduction of a porous silicon (pSi) buffer layer in between Ge and Si. pSi is a versatile, self-assembled, nanomaterial which can be realized at very high growth rates through electrochemical etching of Si. Thanks to its reduced Young’s and shear moduli pSi can deform during epitaxy, potentially alleviating part of the lattice mismatch between Ge and Si and reducing the density of misfit dislocations and associated threading segments necessary for complete Ge relaxation. Together with the very high throughput of the anodization process, other fundamental advantages of the proposed approach are its low cost, its simple scalability to large area Si substrates and the possibility to lift-off the grown epilayers from the starting substrates, giving Ge on pSi VSs the possibility to outperform other existing techniques for Ge integration on Si.
During the course of this work, several Ge on pSi VSs have been grown through low energy plasma enhanced chemical vapor deposition (LEPECVD) technique, and the resulting crystalline quality has been compared to that of Ge on Si VSs. Using X-ray diffraction techniques, together with electron microscopy analysis and selective etching techniques, it will be shown how the main physical parameters of pSi buffers affect the crystalline quality of Ge heteroepilayers. Finally, it will be demonstrated that strong threading dislocation reduction is possible in Ge grown on low porosity pSi buffers compared to Ge on bulk Si, at parity of experimental conditions, and the main mechanisms responsible for crystalline quality improvement in Ge grown on pSi will be uncovered
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Numerical simulation of the temperature distortions in InGaP/GaAs/Ge solar cells working under high concentrating conditions due to voids presence in the solder joint
No full textThe presence of voids in solar cell solder joints causes a modification of the heat fluxes inside the device during its operation, which in turn leads to local increases in cell temperature and thermal resistance. These temperature increases at device surface lead to a modification of the photovoltaic cell voltage map which translates in a drop in cell output power. Moreover, for pv cells working under high concentration conditions such as III-V multi-junction solar cells for terrestrial application, very high temperature increases can arise as a consequence of void presence, both above the void volume and around it, leading in extreme cases to irreversible damages of the device. In this paper a matlab script is implemented to assess the temperature increase at the top surface of a InGaP/GaAs/Ge solar cell, in the device regions lying outside the void coverage area, for different void sizes found in concentrator solar cells. The obtained results are compared to those of finite element method (FEM) simulations, which are based on an equivalent 2.5 D thermal representation of the cell. A good agreement between FEM simulations and the developed thermal model is observed for small and medium size voids, while for larger voids the error between FEM simulations and the developed model becomes not-negligible. An analytical expression is obtained to assess the device thermal resistance in presence of a random distribution on not-interacting voids. The developed model can be used as starting point to assess the influence of void presence on the power performances of InGaP/GaAs/Ge multi-junction solar cells working under high concentrating conditions
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