1,720,956 research outputs found
Ab initio model of carrier transport in diamond
Full text linkWe have investigated the carrier-transport properties of diamond using a first-principles approach. We have employed a full-band Monte Carlo model based on an electronic structure obtained from density-functional theory (DFT) augmented with Heyd-Scuseria-Ernzerhof (HSE) hybrid functionals. We have computed the carrier-phonon interaction directly employing the DFT electronic structure and phonon dispersion. Effective acoustic and optical scattering models have been calibrated against the ab initio results to obtain a computationally efficient transport model that retains the accuracy of the first-principles approach. Using the DFT-derived full-band structure and the calculated carrier-phonon scattering rates, we have evaluated the field-dependent drift velocities and impact-ionization coefficients and compared them to the available experimental data. We have also analyzed the temperature dependence of the carrier drift velocity up to 500 K and developed analytical models that can be used to perform device simulation based on the drift-diffusion method
Design and modeling of asymmetric bow-tie VCSELs for 100 GHz and beyond
Full text linkWe present the design and numerical analysis of an asymmetric bow-tie vertical-cavity
surface-emitting laser (ABT-VCSEL) that enables PAM-2 direct modulation up to 100 GHz.
The device concept relies on photon-photon resonance (PPR) between laterally coupled modes,
triggered by a structural asymmetry introduced via a hollowed dielectric mirror. This approach
avoids the need for asymmetric pumping and probing while ensuring strong modal coupling
under uniform carrier injection. A dynamical in-house suite, combining field-carrier interaction,
electromagnetic, and thermal problems, is developed and discussed to evaluate device performance
under realistic conditions. The simulation results predict a 3-dB bandwidth up to 70 GHz with
low modulation swing, and open eye diagrams at 100 GHz PAM-2 modulation and 70 GHz
PAM-4 modulation. The proposed ABT-VCSEL concept shows robustness against geometrical
variations and ambient temperature when proper cavity detuning is applied, making it a promising
candidate for next-generation ultra-fast short-reach interconnects
Enhanced dynamic properties of Ge-on-Si mode-evolution waveguide photodetectors
Full text linkThis work discusses coupled three-dimensional electromagnetic and electrical simulations of a Ge-on-Si waveguide photodetector where light is fed through a lateral waveguide. The numerical results show that this coupling solution leads to more uniform photon and carrier distributions along the Ge absorber compared to a conventional butt-coupled detector, allowing a broader electrooptical bandwidth for high input power levels in good agreement with available experimental measurements
Different approximations for carriers lifetimes in HgCdTe quasi-neutral regions
Full text linkIn mid- and far-infrared HgCdTe photodetectors, the maximum operating temperature is determined by the dark current, which in turn depends on charge carriers lifetimes. The ability to reduce dark current and operate at the radiative limit allows for significantly higher operating temperature, but in this new scenario some approximations, commonly and historically applied in the literature to estimate and optimize lifetimes and dark current, in some cases should be avoided
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
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