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Farkas, Ildiko
Publications (4 of 4) Show all publications
Minamisawa, R. A., Mihaila, A., Farkas, I., Teodorescu, V. S., Afanasev, V. V., Chih-Wei, C.-W., . . . Rahimo, M. (2016). Characterization of a n+3C/n-4H SiC heterojunction diode. Applied Physics Letters, 108(14), 143502
Open this publication in new window or tab >>Characterization of a n+3C/n-4H SiC heterojunction diode
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2016 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 14, p. 143502-Article in journal (Refereed) Published
Abstract [en]

We report on the fabrication of n+3C/n-4H SiC heterojunction diodes (HJDs) potentially promising the ultimate thermal stability of the junction. The diodes were systematically analyzed by TEM, X-ray diffraction, AFM, and secondary ion mass spectroscopy, indicating the formation of epitaxial 3C-SiC crystal on top of 4H-SiC substrate with continuous interface, low surface roughness, and up to similar to 7 x 10(17) cm(-3) dopant impurity concentration. The conduction band off-set is about 1 V as extracted from CV measurements, while the valence bands of both SiC polytypes are aligned. The HJDs feature opening voltage of 1.65 V, consistent with the barrier height of about 1.5 eV extracted from CV measurement. We finally compare the electrical results of the n+3C/n-4H SiC heterojunction diodes with those featuring Si and Ge doped anodes in order to evaluate current challenges involved in the fabrication of such devices. (C) 2016 AIP Publishing LLC.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-127776 (URN)10.1063/1.4945332 (DOI)000374230700040 ()
Available from: 2016-05-12 Created: 2016-05-12 Last updated: 2017-11-30
Booker, I. D., Farkas, I., Ivanov, I. G., Ul Hassan, J. & Janzén, E. (2016). Chloride-based SiC growth on a-axis 4H-€“SiC substrates. Paper presented at 6th South African Conference on Photonic Materials (SACPM 2015), Mabula Game Lodge, South Africa, 4 – 8 May 2015. Physica. B, Condensed matter, 480, 23-25
Open this publication in new window or tab >>Chloride-based SiC growth on a-axis 4H-€“SiC substrates
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2016 (English)In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 480, p. 23-25Article in journal (Refereed) Published
Abstract [en]

Abstract SiC has, during the last few years, become increasingly important as a power-device material for high voltage applications. The thick, low-doped voltage-supporting epitaxial layer is normally grown by CVD on 4° off-cut 4H–SiC substrates at a growth rate of 5 – 10 ÎŒ m / h using silane (SiH4) and propane (C3H8) or ethylene (C2H4) as precursors. The concentrations of epitaxial defects and dislocations depend to a large extent on the underlying substrate but can also be influenced by the actual epitaxial growth process. Here we will present a study on the properties of the epitaxial layers grown by a Cl-based technique on an a-axis (90° off-cut from c-direction) 4H–SiC substrate.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
4H–SiC; a-face; DLTS; Photoluminescence; Raman; Epitaxy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-123948 (URN)10.1016/j.physb.2015.08.038 (DOI)000365600300005 ()
Conference
6th South African Conference on Photonic Materials (SACPM 2015), Mabula Game Lodge, South Africa, 4 – 8 May 2015
Available from: 2016-01-14 Created: 2016-01-14 Last updated: 2017-11-30Bibliographically approved
Banyai, I., Farkas, I. & Toth, I. (2016). Simple O-17 NMR method for studying electron self-exchange reaction between UO22+ and U4+ aqua ions in acidic solution. Magnetic Resonance in Chemistry, 54(6), 444-450
Open this publication in new window or tab >>Simple O-17 NMR method for studying electron self-exchange reaction between UO22+ and U4+ aqua ions in acidic solution
2016 (English)In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 54, no 6, p. 444-450Article in journal (Refereed) Published
Abstract [en]

O-17 NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of O-17-enrichment in (UOO2+)-O-17 ion in the presence of U4+ ion in aqueous solution. The reactions have been performed at room temperature using I=5MClO(4)(-) ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U4+ and UO22+ aqua ions. The rate equation is given as R = a[H+](-2) + R, where R is an acid independent parallel path. R depends on the concentration of the uranium species according to the following empirical rate equation: R = k(1)[UO2+](1/2)[U4+](1/2) + k(2)[UO2+](3/2)[U4+](1/2). The mechanism of the inverse H+ concentration-dependent path is interpreted as equilibrium formation of reactive UO2+ species from UO22+ and U4+ aqua ions and its electron exchange with UO22+. The determined rate constant of this reaction path is in agreement with the rate constant of UO22+-UO2+, one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO3+, which loses enrichment mainly by electron exchange with UO22+ ions. One can also conclude that O-17 NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes. Copyright (C) 2015 John Wiley amp; Sons, Ltd.

Place, publisher, year, edition, pages
WILEY-BLACKWELL, 2016
Keywords
NMR; O-17 NMR; isotope exchange; electron exchange; uranyl aqua complexes; kinetic analysis; mechanism
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-130668 (URN)10.1002/mrc.4235 (DOI)000379965900005 ()25854521 (PubMedID)
Note

Funding Agencies|Royal Institute of Technology, Stockholm Sweden; ENVIKUT project [TAMOP-4.2.2.A-11/1/KONV-2012-0043]; EU; European Social Fund at the University of Debrecen, Hungary

Available from: 2016-08-20 Created: 2016-08-19 Last updated: 2017-11-28
Ul-Hassan, J., Bae, H., Lilja, L., Farkas, I., Kim, I., Stenberg, P., . . . Janzén, E. (2014). Fast growth rate epitaxy on 4((degrees)under-bar) off-cut 4-inch diameter 4H-SiC wafers. In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2: . Paper presented at 15th International Conference on Silicon Carbide and Related Materials (ICSCRM), Miyazaki, Japan, 29 Sptember - 4 October 2013 (pp. 179-182). Trans Tech Publications, 778-780
Open this publication in new window or tab >>Fast growth rate epitaxy on 4((degrees)under-bar) off-cut 4-inch diameter 4H-SiC wafers
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2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 179-182Conference paper, Published paper (Refereed)
Abstract [en]

We report the development of over 100 mu m/h growth rate process on 4-inch diameter wafers using chlorinated growth. The optimized growth process has shown extremely smooth epilayers completely free of surface step-bunching with very low surface defect density, high uniformity in thickness and doping and high run to run reproducibility in growth rate, controlled doping and defect density.

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 1662-9752 ; 778-780
Keywords
Fast epitaxial growth; high growth rate; chlorinated growth; atomic force microscopy
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-108193 (URN)10.4028/www.scientific.net/MSF.778-780.179 (DOI)000336634100042 ()
Conference
15th International Conference on Silicon Carbide and Related Materials (ICSCRM), Miyazaki, Japan, 29 Sptember - 4 October 2013
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2016-06-02Bibliographically approved
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