1,720,991 research outputs found
Full-Band Quantum Transport of Heterojunction Electron Devices with Empirical Pseudopotentials
No full textThis article presents the methodology, implementation, and application of a full-band quantum transport model based on the nonequilibrium Green's function formalism and the empirical pseudopotentials. In particular, this article reports the treatment of heterojunctions between lattice-matched semiconductors, comprising a gradual transition region described according to a virtual crystal approximation. Our approach entails several numerical techniques to make the full-band quantum transport method computationally affordable and thus enable robust and efficient self-consistent device simulations. Then, we employ our simulation scheme for the analysis of some exemplary devices based on quantum tunneling, such as an Esaki tunneling diode, as well as n- and p-type heterojunction tunnel FETs. In particular, we investigate the influence on the current-voltage characteristics of the width of the heterojunction transition region. We observe that a gradual transition region mainly affects the device characteristics by lengthening the tunneling path at the heterojunction, which has a different impact on device current depending on the external bias conditions
Surface-Roughness-Induced Variability in Nanowire InAs Tunnel FETs
No full textWe present a comparative study of the surfaceroughness
(SR)-induced variability at low supply voltage
VDD = 0.3 V in nanowire InAs tunnel FETs and strained-silicon
(sSi)MOSFETs. By exploiting a 3-D full-quantum approach based
on the Non-Equilibrium Green’s Function formalism, we show
that the Ion variability in InAs tunnel FETs is much smaller
than the Ioff variability, whereas for VDD = 0.3 V, the sSi MOSFETs
working in the subthreshold regime present similar Ion
and Ioff variability. We explain the smaller Ion compared with
Ioff variability of InAs tunnel FETs by noting that in the source
depletion region, where tunnelingmainly occurs for VGS = VDD,
microscopic subband fluctuations induced by SR are small compared
to macroscopic band bending due to the built-in potential
of the source junction and to the gate bias. This results in SR-induced
variability that is larger in InAs tunnel FETs than in sSi
MOSFETs
Impact of Interface Traps on the IV Curves of InAs Tunnel-FETs and MOSFETs: A Full Quantum Study
No full textWe present the first computational study employing a full
quantum transport model to investigate the effect of interface
traps in nanowire InAs Tunnel FETs and MOSFETs. To this
purpose, we introduced a description of interface traps in a
simulator based on the NEGF formalism and on a 8×8 k·p
Hamiltonian and accounting for phonon scattering. Our results
show that: (a) even a single trap can detereorate the inverse
sub-threshold slope (SS) of a nanowire InAs Tunnel FET; (b)
the inelastic phonon assisted tunneling (PAT) through interface
traps results in a temperature dependence of the Tunnel FETs
IV characteristics; (c) the impact of interface traps on Iof f is
larger in Tunnel FETs than in MOSFETs; (d) interface traps
represent a sizable source of device variability
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
Impact of inelastic phonon scattering in the OFF state of Tunnel-field-effect transistors
No full textWe study the impact of electron–phonon interaction on the subthreshold operation region of Tunnel-FETs by means of full-quantum simulations. Our approach is based on the nonequilibrium Green’s function method, where acoustic and optical phonon scatterings are taken into account through the self-consistent Born approximation. Two device architectures are analyzed: InAs nanowire longitudinal Tunnel-FETs, and 2D vertical Tunnel-FETs based on either an GaSb/AlSb/InAs heterostructure or a MoS2/WTe2 van der Waals heterojunction. In InAs nanowire Tunnel-FETs with interface traps, electron–phonon interaction deteriorates the subthreshold swing by allowing trap-assisted tunneling at energies higher than the valence-band edge in the source. In vertical heterojunction Tunnel-FETs, optical phonon scattering increases the OFF current by inducing inelastic transition in the overlap region even in the absence of trap
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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