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Gali, Adam
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Publications (10 of 27) Show all publications
Trinh, X. T., Szasz, K., Hornos, T., Kawahara, K., Suda, J., Kimoto, T., . . . Son, N. T. (2014). Identification of the negative carbon vacancy at quasi-cubic site in 4H-SiC by EPR and theoretical calculations. In: Silicon Carbide and Related Materials 2013, PTS 1 AND 2: . Paper presented at 15th International Conference on Silicon Carbide and Related Materials (ICSCRM 2013), 29 September - 4 October 2013, Miyazaki, Japan (pp. 285-288). Trans Tech Publications Inc., 778-780
Open this publication in new window or tab >>Identification of the negative carbon vacancy at quasi-cubic site in 4H-SiC by EPR and theoretical calculations
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2014 (English)In: Silicon Carbide and Related Materials 2013, PTS 1 AND 2, Trans Tech Publications Inc., 2014, Vol. 778-780, p. 285-288Conference paper, Published paper (Refereed)
Abstract [en]

In freestanding n-type 4H-SiC epilayers irradiated with low-energy (250 keV) electrons at room temperature, the electron paramagnetic resonance (EPR) spectrum of the negative carbon vacancy at the hexagonal site, V-C(-)(h), and a new signal were observed. From the similarity in defect formation and the spin-Hamiltonian parameters of the two defects, the new center is suggested to be the negative C vacancy at the quasi-cubic site, V-C(-)(k). The identification is further supported by hyperfine calculations.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014
Series
Materials Science Forum, ISSN 1662-9752 ; 778-780
Keywords
Carbon vacancy; negative-U behavior; electron irradiation; EPR; supercell calculations
National Category
Ceramics
Identifiers
urn:nbn:se:liu:diva-108197 (URN)10.4028/www.scientific.net/MSF.778-780.285 (DOI)000336634100067 ()
Conference
15th International Conference on Silicon Carbide and Related Materials (ICSCRM 2013), 29 September - 4 October 2013, Miyazaki, Japan
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2014-10-28Bibliographically approved
Ivády, V., Abrikosov, I., Janzén, E. & Gali, A. (2014). Theoretical investigation of the single photon emitter carbon antisite-vacancy pair in 4H-SiC. In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2: . Paper presented at SILICON CARBIDE AND RELATED MATERIALS 2013 (pp. 495-498). Trans Tech Publications, 778-780
Open this publication in new window or tab >>Theoretical investigation of the single photon emitter carbon antisite-vacancy pair in 4H-SiC
2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 495-498Conference paper, Published paper (Refereed)
Abstract [en]

Well addressable and controllable point defects in device friendly semiconductors are desired for quantum computational and quantum informational processes. Recently, such defect, an ultra-bright single photon emitter, the carbon antisite - vacancy pair, was experimentally investigated in 4H-SiC. In our theoretical work, based on ab initio calculation and group theory analysis, we provide a deeper understanding of the features of the electronic structures and the luminescence process of this defect.

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 1662-9752 ; 778-780
Keywords
Point defect; single photon emitter; carbon antisite-vacancy pair
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-108199 (URN)10.4028/www.scientific.net/MSF.778-780.495 (DOI)000336634100116 ()
Conference
SILICON CARBIDE AND RELATED MATERIALS 2013
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2014-06-26
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, p. 405-408Conference 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
Keywords
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
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, p. 211-216Conference 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
Keywords
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
Son, N. T., Ivady, V., Gali, A., Gällström, A., Leone, S., Kordina, O. & Janzén, E. (2012). Identification of Niobium in 4H-SiC by EPR and ab Initio Studies. 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. 217-220). Trans Tech Publications Inc., 717-720
Open this publication in new window or tab >>Identification of Niobium in 4H-SiC by EPR and ab Initio Studies
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2012 (English)In: Materials Science Forum Vols 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, p. 217-220Conference paper, Published paper (Refereed)
Abstract [en]

In unintentionally Nb-doped 4H-SiC grown by high-temperature chemical vapor deposition (HTCVD), an electron paramagnetic resonance (EPR) center with C-lh symmetry and an electron spin S=1/2 was observed. The spectrum shows a hyperfine structure consisting of ten equal-intensity hyperfine (hf) lines which is identified as due to the hf interaction between the electron spin and the nuclear spin of Nb-93. An additional hf structure due to the interaction with two equivalent Si neighbors was also observed. Ab initio supercell calculations of Nb in 4H-SiC suggest that Nb may form a complex with a C-vacancy (V-C) resulting in an asymmetric split-vacancy (ASV) defect, Nb-Si-V-C. Combining results from EPR and supercell calculations, we assign the observed Nb-related EPR center to the hexagonal-hexagonal configuration of the AVS defect in the neutral charge state, (Nb-Si-V-C)(0).

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
Keywords
Transition metal impurity; split-vacancy defect; electron paramagnetic resonance; ab initio calculations
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-87571 (URN)10.4028/www.scientific.net/MSF.717-720.217 (DOI)000309431000050 ()
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: 2016-06-02
Ivady, V., Somogyi, B., Zolyomi, V., Gällström, A., Son, N. T., Janzén, E. & Gali, A. (2012). Transition Metal Defects in Cubic and Hexagonal Polytypes of SiC: Site Selection, Magnetic and Optical Properties from ab initio Calculations. In: Materials Science Forum Vol 717 - 720. Paper presented at 14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA (pp. 205-210). Trans Tech Publications Inc., 717-720
Open this publication in new window or tab >>Transition Metal Defects in Cubic and Hexagonal Polytypes of SiC: Site Selection, Magnetic and Optical Properties from ab initio Calculations
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2012 (English)In: Materials Science Forum Vol 717 - 720, Trans Tech Publications Inc., 2012, Vol. 717-720, p. 205-210Conference paper, Published paper (Refereed)
Abstract [en]

Relatively little is known about the transition metal defects in silicon carbide (SiC). In this study we applied highly convergent and sophisticated density functional theory (DFT) based methods to investigate important transition metal impurities including titanium (Ti), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo) and tungsten (W) in cubic 3C and hexagonal 4H and 6H polytypes of SiC. We found two classes among the considered transition metal impurities: Ti, V and Cr clearly prefer the Si-substituting configuration while W, Nb, and Mo may form a complex with a carbon vacancy in hexagonal SiC even under thermal equilibrium with similar concentration. If the metal impurity is implanted into SiC or when many carbon impurities exist during the growth of SiC then complex formation between the Si-substituting metal impurity and the carbon vacancy should be considered. This complex pair configuration exclusively prefers the hexagonal-hexagonal sites in hexagonal polytypes and may be absent in the cubic polytype. We also studied transition metal doped nano 3C-SiC crystals in order to check the effect of the crystal field on the d-orbitals of the metal impurity.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2012
Keywords
point defects; hybrid density functional theory; transition metals; electron paramagnetic resonance; photoluminescence; site selection; polytypes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88453 (URN)10.4028/www.scientific.net/MSF.717-720.205 (DOI)000309431000048 ()
Conference
14th International Conference on Silicon Carbide and Related Materials (ICSCRM 2011), 11-16 September 2011, Cleveland, OH, USA
Available from: 2013-02-12 Created: 2013-02-07 Last updated: 2013-02-21
Gali, A., Gällström, A., Son, N. T. & Janzén, E. (2010). Theory of neutral divacancy in SiC: a defect for spintronics. In: Materials Science Forum, Vols. 645-648. Paper presented at ICSCRM 2009 (pp. 395-397). Trans Tech Publications
Open this publication in new window or tab >>Theory of neutral divacancy in SiC: a defect for spintronics
2010 (English)In: Materials Science Forum, Vols. 645-648, Trans Tech Publications , 2010, p. 395-397Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Trans Tech Publications, 2010
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-62704 (URN)
Conference
ICSCRM 2009
Available from: 2010-12-02 Created: 2010-12-02 Last updated: 2012-04-03
Nguyen, S. T., Isoya, J., Morishita, N., Ohshima, T., Itoh, H., Gali, A. & Janzén, E. (2009). Defects introduced by electron-irradiation at low temperatures in SiC. In: Materials Science Forum Vols. 615-617: . Paper presented at 7th European Conference on Silicon Carbide and Related Materials, ECSCRM 2008; Barcelona; Spain (pp. 377-380). Trans Tech Publicarions
Open this publication in new window or tab >>Defects introduced by electron-irradiation at low temperatures in SiC
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2009 (English)In: Materials Science Forum Vols. 615-617, Trans Tech Publicarions , 2009, p. 377-380Conference paper, Published paper (Refereed)
Abstract [en]

Defects introduced by electron irradiation at ~80-100 K in 3C-, 4H- and 6H-SiC were studied by electron paramagnetic resonance (EPR). A number of EPR spectra, labelled LE1-10, were detected. Combining EPR and supercell calculations, we will show that the LE1 center in 3C-SiC with C2v symmetry and an electron spin S=3/2 is related to the (VSi-Sii)3+ Frenkel pair between the silicon vacancy and a second neighbour Sii interstitial along the <100> direction. Results on other centers, possibly also related to interstitials, are discussed.

Place, publisher, year, edition, pages
Trans Tech Publicarions, 2009
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-43504 (URN)10.4028/www.scientific.net/MSF.615-617.377 (DOI)73991 (Local ID)978-087849334-0 (ISBN)73991 (Archive number)73991 (OAI)
Conference
7th European Conference on Silicon Carbide and Related Materials, ECSCRM 2008; Barcelona; Spain
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2014-09-04
Nguyen, S. T., Janzén, E., Isoya, J., Morishita, N., Hanaya, H., Takizawa, H., . . . Gali, A. (2009). Identification of a Frenkel-pair defect in electron-irradiated 3C SiC. Physical Review B. Condensed Matter and Materials Physics, 80, 125201
Open this publication in new window or tab >>Identification of a Frenkel-pair defect in electron-irradiated 3C SiC
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2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, p. 125201-Article in journal (Refereed) Published
Abstract [en]

Anelectron paramagnetic resonance (EPR) spectrum labeled LE1 was observed inn-type 3C SiC after electron irradiation at low temperatures (~80–100  K).A hyperfine interaction with four nearest C neighbors similar tothat of the well-known silicon vacancy in the negative chargestate was observed, but the LE1 center has a lowersymmetry, C2v. Supercell calculations of different configurations of silicon vacancy-interstitialFrenkel-pairs, VSi-Sii, were performed showing that pairs with a nearestneighbor Si interstitial are unstable—VSi and Sii will automatically recombine—whereaspairs with a second neighbor Sii are stable. Comparing thedata obtained from EPR and supercell calculations, the LE1 centeris assigned to the Frenkel-pair between VSi and a secondneighbor Sii interstitial along the [100] direction in the 3+charge state, V-Si. In addition, a path for the migrationof Si was found in 3C SiC. In samples irradiatedat low temperatures, the LE1 Frenkel-pair was found to bethe dominating defect whereas EPR signals of single vacancies werenot detected. The center disappears after warming up the samplesto room temperature.

Keywords
electron beam effects, Frenkel defects, hyperfine interactions, interstitials, paramagnetic resonance, silicon compounds, wide band gap semiconductors
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-50688 (URN)10.1103/PhysRevB.80.125201 (DOI)
Available from: 2009-10-13 Created: 2009-10-13 Last updated: 2017-12-12
Gali, A., Umeda, T., Janzén, E., Morishita, N., Ohshima, T. & Isoya, J. (2009). Identification of the Di-Carbon Antisite Defect in n-type 4H-SiC. In: Materials Science Forum Vols. 615-617. Paper presented at ECSCRM2008 (pp. 361). Trans Tech Publications
Open this publication in new window or tab >>Identification of the Di-Carbon Antisite Defect in n-type 4H-SiC
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2009 (English)In: Materials Science Forum Vols. 615-617, Trans Tech Publications , 2009, p. 361-Conference paper, Published paper (Refereed)
Abstract [en]

  

Place, publisher, year, edition, pages
Trans Tech Publications, 2009
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-43527 (URN)74085 (Local ID)74085 (Archive number)74085 (OAI)
Conference
ECSCRM2008
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2010-12-15
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