186,374 research outputs found
Formation of Ti ohmic contact on p-SiC by laser annealing
No full textSilicon carbide (4H-SiC) Schottky barrier diodes with a mature technological level and a large variety of products, targeted for different voltage and current values, are now commercially available [1]. Although significant progresses in 4H-SiC devices technology have been recorded in the last decade, there are still some challenging aspects hindering the achievement of devices operating at the theoretical limits, mainly related to surface and interface processing [2,3]. As an example, the formation of good- quality Ohmic contacts to p-type doped SiC still represents a critical issue. Nickel has been widely used as Ohmic contact to p-type 4H-SiC following silicidation at annealing temperatures above 900◦C [4]. Another good candidate to obtain ohmic contact is Titanium (Ti). In fact, reaction between Ti layer and the p-type 4H-SiC emphasizes the role of the ternary phase Ti3SiC2 formed at the interface as responsible for the barrier height lowering and Ohmic behavior [5–7]. For the Ohmic contacts formation, rapid thermal annealing (RTA) was conventionally used. However, during the fabrication process of 4H-SiC power devices, the RTA method causes unnecessarily heating of the whole structure and not only of the contacts. Therefore, a local annealing method for silicidation has become necessary. In this context, a nanosecond non-equilibrium laser annealing (LA) for the metal/4H-SiC silicidation process is a method that could help to overcome the RTA limits [8,9].
In this study, we systematically investigate the influence of the LA conditions, both in terms of energy density in the range 2.0-3.8 J/cm2 and number of shots (n) from 1 to 10, on the properties of Ti-based Ohmic contact on p-type 4H-SiC. In particular, the electrical properties of Ti/4H-SiC Ohmic contacts processed under different LA conditions will be correlated with the structural ones.
The starting material was a commercial n-type 4H-SiC wafer. On this sample, transmission line model (TLM) devices were fabricated by using Al implantion for p-type doping and 20 nm Ti deposited by e- beam evaporation for the Ohmic contact. Fig.1 shows the representative I-V characteristics of the devices for two different energy densities. The measurements are acquired between two adjacent pads of TLM structures at different distances from 10 to 50 μm, with 10 μm step. Up to 3.4 J/cm2 (Fig. 1a) the characteristics do not show either a dependence on the TLM pad distance or a linear behavior. Instead, the sample irradiated at the higher fluence from 3.6 J/cm2 (Fig. 1b) shows linear I−V characteristics, with a total resistance increasing with the pad distance. Fig. 2 shows the contact resistance (RC) values as a function of LA energy density. Increasing LA energy density leads to a decrease of the contact resistance values of about one order of magnitude. On the other hand, the increase of number of shots leads to higher RC values. Furthermore, we have studied the behavior of the current, acquired at 1V between two adjacent pads, by fixing the energy density and varying the number of shots. Fig. 3 shows variation of current at different n, spanning from 1 to 10 shots, for 3.4 and 3.6 J/cm2 LA energies. It is possible to observe that the current varies differently with the number of shots in the two cases. For energy density of 3.4 J/cm2 we can observe a first decrease up to 6 shots and then an increment. This behavior is similar to the one observed by Choi et al. [10] and can be related to the different C thickness induced by LA of SiC [11]. On the other hand, the current for the energy density of 3.6 J/cm2 continues to drop down by increasing the number of shots.
To confirm this point, additional microstructural analyses are in progress to understand if the evolution of the contact properties is linked with C formation. In the extended paper, a systematic investigation of all the process parameters (LA, C-thickness Ti/4H-SiC interface) will be presented, highlighting their role in controlling the electrical characteristics of the Ohmic contact
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
A novel experiment approach to ohmic contact formation on p-doped SiC
No full textIn this work, the fabrication of a novel configuration for an ohmic contact on p-doped SiC substrate, employing laser treatment instead of the conventional oven treatment, is analyzed. Test patterns made by Ti rectangular contacts on p-SiC were fabricated. The overall structure is treated with an excimer laser, employing different energy densities and number of shots. In particular, the laser energy density ranges from 1.0 J/cm2 to 3.8 J/cm2 and the number of shots from 1 to 10. The analysis shows that the system begins to exhibit an ohmic behavior when exposed to laser energy densities of 3.6 J/cm2 and above. Also, the number of shots influences the electrical behavior, with higher values leading to losing the linearity in the I-V curves. The best performance, characterized by the lowest resistivity value, is observed with an energy density value of 3.8 J/cm2 and 1 laser shot applied. Under these conditions, the resistivity value is 1.4x10-2 Ωcm, or in terms of specific resistivity 7x10-5 Ωcm2, the contact resistance is 152 Ω and the sheet resistance is 656 Ω/sq. This work enables the achievement of an ohmic contact between Titanium and p doped SiC, overcoming the challenge of using high temperature oven treatment
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
No full textWe 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
Dr. Edward P. Wimberly, ITC, July 2011
No full textThis video is a conversation with Dr. Edward P. Wimberly. Dr. Wimberly talks about his book, "No Shame in Wesley's Gospel: A Twenty-First Century Pastoral Gospel". Brad Ost, AUC Woodruff Library, is the interviewer
Author Rights and Scholarly Publishing
No full textOriginally posted at
http://blog.library.gsu.edu/2014/10/24/author-rights-and-scholarly-publishing/</p
Ohmic contact formation on p-doped 4H-SiC using pulsed laser annealing
No full textIn this work, the fabrication of a novel configuration for an ohmic contact on p doped SiC substrate, employing laser treatment instead of the con- ventional oven treatment, is analyzed. Test-patterns made by Ti rectangular contacts on p-SiC were fabricated. The overall structure is treated with an ex- cimer laser, employing different energy densities and number of shots. In par- ticular, the laser energy density ranges from 1.0 J/cm2 to 3.8 J/cm2 and the number of shots from 1 to 10. The analysis shows that the system begins to ex- hibit an ohmic behavior when exposed to laser energy densities of 3.6 J/cm2 and above. Also, the number of shots influences the electrical behavior, with higher values leading to losing the linearity in the I-V curves. The best performance, characterized by the lowest resistivity value, is observed with an energy density value of 3.8 J/cm2 and 1 laser shot applied. Under these conditions, the resistivi- ty value is 1.4x10-2 Ωcm or 7x10-5 Ωcm2, the contact resistance RC is 152 Ω and the sheet resistance Rsh 372 Ω/cm2. This work enables the achievement of an ohmic contact between Titanium and p doped SiC, overcoming the challenge of using high temperature oven treatment
- …
