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Leone, Stefano
Alternative names
Publications (10 of 43) Show all publications
Gällström, A., Magnusson, B., Leone, S., Kordina, O., Son, N. T., Ivády, V., . . . Ivanov, I. G. (2015). Optical properties and Zeeman spectroscopy of niobium in silicon carbide. Physical Review B. Condensed Matter and Materials Physics, 92(7), 1-14, Article ID 075207.
Open this publication in new window or tab >>Optical properties and Zeeman spectroscopy of niobium in silicon carbide
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2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 92, no 7, 1-14 p., 075207Article in journal (Refereed) Published
Abstract [en]

The optical signature of niobium in the low-temperature photoluminescence spectra of three common polytypes of SiC (4H, 6H, and 15R) is observed and confirms the previously suggested concept that Nb occupies preferably the Si-C divacancy with both Si and C at hexagonal sites. Using this concept we propose a model considering a Nb-bound exciton, the recombination of which is responsible for the observed luminescence. The exciton energy is estimated using first-principles calculation and the result is in very good agreement with the experimentally observed photon energy in 4H SiC at low temperature. The appearance of six Nb-related lines in the spectra of the hexagonal 4H and 6H polytypes at higher temperatures is tentatively explained on the grounds of the proposed model and the concept that the Nb center can exist in both C1h and C3v symmetries. The Zeeman splitting of the photoluminescence lines is also recorded in two different experimental geometries and the results are compared with theory based on phenomenological Hamiltonians. Our results show that Nb occupying the divacancy at the hexagonal site in the studied SiC polytypes behaves like a deep acceptor.

Place, publisher, year, edition, pages
American Physical Society, 2015
National Category
Theoretical Chemistry Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-117972 (URN)10.1103/PhysRevB.92.075207 (DOI)000362204100001 ()
Note

At the time for thesis presentation publication was in status: Manuscript

Funding Agencies|Knut and Alice Wallenberg Foundation; Lendulet program of the Hungarian Academy of Sciences; Hungarian OTKA Project [K101819]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D. I. Mendeleev Fund Program [8.1.18.2015]

Available from: 2015-05-19 Created: 2015-05-19 Last updated: 2017-12-04Bibliographically approved
Leone, S., Henry, A., Janzén, E. & Nishizawa, S. (2013). Epitaxial growth of SiC with chlorinated precursors on different off-angle substrates. Journal of Crystal Growth, 362, 170-173.
Open this publication in new window or tab >>Epitaxial growth of SiC with chlorinated precursors on different off-angle substrates
2013 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 362, 170-173 p.Article in journal (Refereed) Published
Abstract [en]

This study focuses on the epitaxial growth of silicon carbide (SiC) epitaxial layers, adopting the chloride-based chemical-vapor-deposition (CVD) process, which allows to achieve ten times higher growth rate compared to the standard process based on the mixture of a silicon-containing gas and a hydrocarbon. In order to improve the material quality, substrates with different off-angles were used, since low off-angle substrates result in a reduction of killer defects for specific devices. Different growth mechanisms dominate for different substrate off-cut and an accurate set up of dedicated surface preparation procedures and tuning of growth parameters are needed. This study demonstrates that silicon-rich gas inputs are favorable for lower off-angle (nominally on-axis) substrates, while carbon-rich are beneficial for higher off-angles (usually 8 degrees off-axis for 4H-SiC). Methyltrichlorosilane (MTS) is shown to be the best precursor to achieve the presented results.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Crystal morphology; Chemical vapor deposition processes; Chloride vapor phase epitaxy; Semiconducting silicon compounds
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87196 (URN)10.1016/j.jcrysgro.2011.09.061 (DOI)000311647400038 ()
Available from: 2013-01-14 Created: 2013-01-14 Last updated: 2017-12-06
Gueorguiev Ivanov, I., Gällström, A., Leone, S., Kordina, O., Tien Son, N., Henry, A., . . . Janzén, E. (2013). Optical properties of the niobium centre in 4H, 6H, and 15R SiC. In: SILICON CARBIDE AND RELATED MATERIALS 2012: . Paper presented at 9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012) (pp. 405-408). Trans Tech Publications, 740-742.
Open this publication in new window or tab >>Optical properties of the niobium centre in 4H, 6H, and 15R SiC
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2013 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2012, Trans Tech Publications , 2013, Vol. 740-742, 405-408 p.Conference paper, Published paper (Refereed)
Abstract [en]

A set of lines in the photoluminescence spectra of 4H-, 6H-, and 15R-SiC in the near-infrared are attributed to Nb-related defects on the ground of doping experiments conducted with 4H-SiC. A model based on a an exciton bound at the Nb-centre in an asymmetric split vacancy configuration at a hexagonal site is proposed, which explains the structure of the luminescence spectrum and the observed Zeeman splitting of the lines.

Place, publisher, year, edition, pages
Trans Tech Publications, 2013
Keyword
transition metals; niobium; photoluminescence; Zeeman effect
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-96515 (URN)10.4028/www.scientific.net/MSF.740-742.405 (DOI)000319785500095 ()
Conference
9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012)
Available from: 2013-08-21 Created: 2013-08-20 Last updated: 2014-10-08
Yazdanfar, M., Leone, S., Pedersen, H., Kordina, O., Henry, A. & Janzén, E. (2012). Carrot defect control in chloride-based CVD through optimized ramp up conditions. In: Materials Science Forum Vols 717 - 720. Paper presented at 14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA (pp. 109-112). Trans Tech Publications Inc., 717-720.
Open this publication in new window or tab >>Carrot defect control in chloride-based CVD through optimized ramp up conditions
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2012 (English)In: Materials Science Forum Vols 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, 109-112 p.Conference paper, Published paper (Refereed)
Abstract [en]

Epitaxial growth of 4H-SiC on 8 degrees off-axis substrates has been performed under different condition during the temperature ramp up in order to study the effect on the carrot defect. The study was done in a hot wall chemical vapor deposition reactor using the single molecule precursor methyltrichlorosilane (MTS). During the temperature ramp up, a small flow of HCl or C2H4 was added to the H-2 ambient to study different surface etching conditions. The best result was obtained when HCl was added from 1175 to 1520 degrees C during the ramp up to growth temperature (1575 degrees C).

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
Keyword
Carrot defects; Chloride-based CVD; Ramp up condition
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87565 (URN)10.4028/www.scientific.net/MSF.717-720.109 (DOI)000309431000025 ()
Conference
14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2015-03-11
Pedersen, H., Leone, S., Kordina, O., Henry, A., Nishizawa, S.-i., Koshka, Y. & Janzén, E. (2012). Chloride-Based CVD Growth of Silicon Carbide for Electronic Applications. Chemical Reviews, 112(4), 2434-2453.
Open this publication in new window or tab >>Chloride-Based CVD Growth of Silicon Carbide for Electronic Applications
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2012 (English)In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 112, no 4, 2434-2453 p.Article, review/survey (Refereed) Published
Abstract [en]

n/a

Place, publisher, year, edition, pages
American Chemical Society, 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-78588 (URN)10.1021/cr200257z (DOI)000303283900015 ()
Note
Funding Agencies|Swedish Research Council||Swedish Energy Agency||Swedish Foundation for Strategic Research||Office of Naval Research||National Science Foundation||Available from: 2012-06-15 Created: 2012-06-15 Last updated: 2017-12-07
Leone, S., Pedersen, H., Beyer, F., Andersson, S., Kordina, O., Henry, A., . . . Janzén, E. (2012). Chloride-Based CVD of 4H-SiC at High Growth Rates on Substrates with Different Off-Angles. In: Materials Science Forum Vols 717 - 720. Paper presented at 14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA (pp. 113-116). Trans Tech Publications Inc., 717-720.
Open this publication in new window or tab >>Chloride-Based CVD of 4H-SiC at High Growth Rates on Substrates with Different Off-Angles
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2012 (English)In: Materials Science Forum Vols 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, 113-116 p.Conference paper, Published paper (Refereed)
Abstract [en]

A review of recently achieved results with the chloride-based CVD on 8 degrees and 4 degrees off-axis and nominally on-axis 4H-SiC wafers is done to clarify the epitaxial growth mechanisms on different off-angle substrates. The process conditions selected for each off-axis angle become even more difficult when running at growth rates of 100 mu m/h or more. A fine-tuning of process parameters, mainly temperature, C/Si ratio and in situ surface preparation is necessary for each Wangle. Some trends related to the surface properties and the effective C/Si ratio existing on the surface prior to and during the epitaxial growth can be observed.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
Keyword
Chloride-based CVD; homoepitaxial growth; substrate off-angle; high growth rate
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87566 (URN)10.4028/www.scientific.net/MSF.717-720.113 (DOI)000309431000026 ()
Conference
14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2015-03-11
Henry, A., Li, X., Leone, S., Kordina, O. & Janzén, E. (2012). CVD growth of 3C-SiC on 4H-SiC substrate. In: Materials Science Forum Vol 711. Paper presented at HeteroSiC & WASMPE 2011 (pp. 16-21). Trans Tech Publications Inc., 711.
Open this publication in new window or tab >>CVD growth of 3C-SiC on 4H-SiC substrate
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2012 (English)In: Materials Science Forum Vol 711, Trans Tech Publications Inc., 2012, Vol. 711, 16-21 p.Conference paper, Published paper (Refereed)
Abstract [en]

The hetero epitaxial growth of 3C-SiC on nominally on-axis 4H-SiC is reported. A horizontal hot-wall CVD reactor working at low pressure is used to perform the growth experiments in a temperature range of 1200-1500 °C with the standard chemistry using silane and propane as precursors carried by a mix of hydrogen and argon. The optimal temperature for single-domain growth is found to be about 1350 °C. The ramp up-conditions and the gas-ambient atmosphere when the temperature increases are key factors for the quality of the obtained 3C layers. The best pre-growth ambient found is carbon rich environment; however time of this pre-treatment is crucial. A too high C/Si ratio during growth led to polycrystalline material whereas for too low C/Si ratios Si cluster formation is observed on the surface. The addition of nitrogen gas is also explored.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-79057 (URN)10.4028/www.scientific.net/MSF.711.16 (DOI)000302673900003 ()
Conference
HeteroSiC & WASMPE 2011
Available from: 2012-06-28 Created: 2012-06-28 Last updated: 2014-10-08
Li, X., Leone, S., Andersson, S., Kordina, O., Henry, A. & Janzén, E. (2012). CVD Heteroepitaxial Growth of 3C-SiC on 4H-SiC (0001) Substrates. In: Materials Science Forum Vols 717 - 720. Paper presented at 14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA (pp. 189-192). Trans Tech Publications Inc., 717-720.
Open this publication in new window or tab >>CVD Heteroepitaxial Growth of 3C-SiC on 4H-SiC (0001) Substrates
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2012 (English)In: Materials Science Forum Vols 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, 189-192 p.Conference paper, Published paper (Refereed)
Abstract [en]

This study has been focused on 3C-SiC epitaxial growth on 4H-SiC (0001) on-axis substrates using the standard CVD chemistry. Several growth parameters were investigated, including growth temperature, in-situ etching process and C/Si ratio. High quality single domain 3C epilayers could be obtained around 1350 degrees C, with propane present during pre-growth etching and when the C/Si ratio was equal to 1. The best grown layer is 100% 3C-SiC and single domain. The net n-type background doping is around 2x10(16) cm(-3). The surface roughness of the layers from AFM analysis is in the 3 to 8 nm range on a 50x50 mu m(2) area.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
Keyword
heteroepitaxial growth; CVD; 3C-SiC
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87569 (URN)10.4028/www.scientific.net/MSF.717-720.189 (DOI)000309431000045 ()
Conference
14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2014-10-08
Son Tien, N., Trinh, X. T., Gällström, A., Leone, S., Kordina, O., Janzén, E., . . . Gali, A. (2012). Electron paramagnetic resonance and theoretical studies of Nb in 4H- and 6H-SiC. Journal of Applied Physics, 112(8), 083711.
Open this publication in new window or tab >>Electron paramagnetic resonance and theoretical studies of Nb in 4H- and 6H-SiC
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2012 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 8, 083711- p.Article in journal (Refereed) Published
Abstract [en]

High purity silicon carbide (SiC) materials are of interest from high-power high temperature applications across recent photo-voltaic cells to hosting solid state quantum bits, where the tight control of electrically, optically, and magnetically active point defects is pivotal in these areas. 4H- and 6H-SiC substrates are grown at high temperatures and the incorporation of transition metal impurities is common. In unintentionally Nb-doped 4H- and 6H-SiC substrates grown by high-temperature chemical vapor deposition, an electron paramagnetic resonance (EPR) spectrum with C-1h symmetry and a clear hyperfine (hf) structure consisting of ten equal intensity hf lines was observed. The hf structure can be identified as due to the interaction between the electron spin S - 1/2 and the nuclear spin of Nb-93. Additional hf structures due to the interaction with three Si neighbors were also detected. In 4H-SiC, a considerable spin density of similar to 37.4% was found on three Si neighbors, suggesting the defect to be a complex between Nb and a nearby carbon vacancy (V-C). Calculations of the Nb-93 and Si-29 hf constants of the neutral Nb on Si site, Nb-Si(0), and the Nb-vacancy defect, NbSiVC0, support previous reported results that Nb preferentially forms an asymmetric split-vacancy (ASV) defect. In both 4H- and 6H-SiC, only one Nb-related EPR spectrum has been observed, supporting the prediction from calculations that the hexagonal-hexagonal defect configuration of the ASV complex is more stable than others.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-86385 (URN)10.1063/1.4759362 (DOI)000310597500056 ()
Note

Funding Agencies|Swedish Energy Agency||Swedish Research Council VR/Linne Environment LiLI-NFM, FP7|270197|NHDP|TAMOP-4.2.1/B-09/1/KMR-2010-0002|Swedish National Infrastructure for Computing||Knut and Alice Wallenberg Foundation||

Available from: 2012-12-14 Created: 2012-12-14 Last updated: 2017-12-06
Gällström, A., Magnusson, B., Beyer, F., Gali, A., Son, N. ., Leone, S., . . . Janzén, E. (2012). Electronic Configuration of Tungsten in 4H-, 6H-, and 15R-SiC. In: Materials Science Forum Vols 717 - 720: . Paper presented at 14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA (pp. 211-216). Trans Tech Publications Inc., 717-720.
Open this publication in new window or tab >>Electronic Configuration of Tungsten in 4H-, 6H-, and 15R-SiC
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2012 (English)In: Materials Science Forum Vols 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, 211-216 p.Conference paper, Published paper (Refereed)
Abstract [en]

A commonly observed unidentified photoluminescence center in SiC is UD-1. In this report, the UD-1 center is identified to be tungsten related. The identification is based on (i) a W-doping study, the confirmation of W in the samples was made using deep level transient spectroscopy (DLTS), (ii) the optical activation energy of the absorption of UD-1 in weakly n-type samples corresponds to the activation energy of the deep tungsten center observed using DLTS. The tungsten-related optical centers are reported in 4H-, 6H-, and 15R-SiC. Further, a crystal field model for a tungsten atom occupying a Si-site is suggested. This crystal field model is in agreement with the experimental data available: polarization, temperature dependence and magnetic field splitting.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
Keyword
deep level defect; PL; transition metal; Crystal Field Model
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87570 (URN)10.4028/www.scientific.net/MSF.717-720.211 (DOI)000309431000049 ()978-3-03785-419-8 (ISBN)
Conference
14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA
Available from: 2013-01-18 Created: 2013-01-18 Last updated: 2015-09-22
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