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Analysis of the hole transport through valence band states in heavy Al doped 4H-SiC by ion implantation
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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
Preparation of Ni2Si contacts: effect on SiC diode operation
No full textThe excellent electrical and thermal properties of SiC make it a preferable semiconductor material for high-power and high temperature devices. A complete exploitation of the properties of SiC needs the manufacturing of low resistivity ohmic contacts stable at high temperatures. Ni/SiC contacts have been studied in order to achieve very low contact resistivity values on n-type SiC. From the first studies, it was observed that, a good ohmic contact can be made by annealing the nickel film at 900-950°C [1] in order to form nickel silicide (Ni2Si), which consumes a SiC layer by solid-state reaction, rising an interface at a larger depth inside the material.
A 10m thick 6H-SiC p-type epilayer with 7.51015cm-3 nominal carrier concentration, underwent a selective phosphorous multiple implantation at 300°C, in order to achieve a box-shaped doping profile 200nm deep and 11020cm-3 high. The sample was annealed at 1300°C for 20 minutes in argon. A Ni layer 50nm thick was evaporated on the front of the wafer and defined by the lift-off technique in order to achieve contacts on the n+ regions. The back contact was made up of an Ti and Al alloy. A first electrical characterization (IV, CV, DLTS) was carried out. The samples subsequently underwent an alloy treatment at 900°C for 1 minute in vacuum in order to form nickel silicide. The diodes were electrically characterized by IV, CV, and TLM measurements. DLTS and EBIC analyses were carried out.
Preliminary TLM measurements show the ohmic behaviour of the alloyed contact, yielding a contact resistivity value around 0.001 IV measurements evidenced some changes in the diode operation: an excess forward current arises in some diodes after the alloy treatment. A degradation of the reverse leakage current was observed as well. Two hypotheses were made on the cause of this change:
1) The further annealing induces the formation of electrically active defects, which act as generation-recombination centres in the current transport.
2) The reaction for the formation of nickel silicide consumes the n+ regions in one or more points, and a small Schottky diode in parallel with the n+/p junction is responsible of the increase of the current.
The formation of defects was investigated by DLTS, the presence of a localised region with different conduction properties was investigated by EBIC analyses.
The analyses show that no further defects are present in the device. A highly conductive layer (fig. 1) was observed by EBIC in the devices where the increase in forward current is most pronounced.
(a) (b)
(c) (d)
Figure 1. SEM (a,c) and EBIC (b,d) images of the conductive area at 15 kV (a,b) and 7.5 kV (c,d) beam energy and 5200x magnification.
[1] L. M. Porter, R. F. Davis, Mater. Sci. Eng. B 34 (1995) 83
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
Charge particle detection properties of epitaxial 4H-SiC Schottky diodes
No full textThis work presents measurements of the charge-collection properties of 4H-SiC Schottky diodes under alpha radiation and investigates the influence of native and alpha induced defects on the detector performance. The contribution of the diffusion of minority carriers to the charge collection efficiency is pointed out. Vaues of 500 ns and 95 us are inferred for the hole and electron lifetime respectively
Characterization of a thermal oxidation process on SiC preamorphized by Ar ion implantation
No full textIn this paper we investigate the thermal growth of SiO2 films on Ar+ amorphized 6H-SiC. The experimental conditions to grow oxide layers on SiC with high oxidation rate at low temperature have been determined. Rutehrford Back Scattering Channelling (RBS-C), Secondary Ion Mass Spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) analyses show the presence of a C rich fim at the SiC infiterface. The thickness of this layers increases as the oxidation time increases to that after 390 min a SiO2Cx transition region as thick as 118 nm has been evidenced between the pure stoichiometric layer of SiO2 and the SiC substrat
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