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Träfflista för sökning "WFRF:(Gali Adam) "

Sökning: WFRF:(Gali Adam)

  • Resultat 1-10 av 35
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1.
  • Aradi, B, et al. (författare)
  • Boron centers in 4H-SiC
  • 2001
  • Ingår i: Materials science Forum, Vols. 353-356. ; s. 455-458
  • Konferensbidrag (refereegranskat)abstract
    • The origin of the "deep boron related acceptor level" in SIC is subject to a lot of controversy. Based on ENDOR investigations, a B-Si+V-C model was suggested, while PL studies indicated the acceptor on the carbon sublattice. Our former ab initio LDA molecular cluster calculation showed that in the B-Si+V-C complex the carbon vacancy acts as the acceptor. Now, ah initio LDA supercell calculations have been carried out for boron-related complexes to calculate the occupation levels in 4H-SiC. It has been found that the 0/- level for the B-Si+V-C complex lies in the upper half of the gap, therefore it can be disregarded as the origin of the "deep boron-related acceptor level". Investigating other feasible boron-related complexes, B-Si+Si-C appears to be the best candidate.
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2.
  • Aradi, B, et al. (författare)
  • Impurity-controlled dopant activation - The role of hydrogen in p-type doping of SiC
  • 2002
  • Ingår i: Materials Science Forum, Vols. 389-393. ; s. 561-564
  • Konferensbidrag (refereegranskat)abstract
    • Hydrogen is a natural contaminant of SiC growth processes, and may influence the doping efficiency. Hydrogen incorporation proportional to that of boron was observed during CVD growth while the amount of hydrogen was two orders of magnitude less than the aluminum concentration. Passivation by complex formation with hydrogen has been proven both for Al and B. The experimentally observed reactivation energy of these complexes differ by 0.9 eV. Our ab initio supercell calculations in 4H-SiC indicate, that in the absence of hydrogen, boron is incorporated as isolated substitutional and prefers the carbon site, while under typical CVD conditions boron is incorporated together with hydrogen (in equal amounts), favoring the silicon site. Therefore, the presence of H is advantageous for the activation of B as a shallow acceptor. In contrast to boron, aluminum is incorporated independently of the presence of hydrogen as isolated substitutional at the silicon site. The calculated difference between the dissociation of the stable dopant plus hydrogen complexes agrees very well with experiments. Vibration frequencies for the dopant complexes have been also calculated.
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3.
  • Aradi, B., et al. (författare)
  • Passivation of p-type dopants in 4H-SiC by hydrogen
  • 2001
  • Ingår i: Physica B, Vols. 308-310. ; s. 722-725
  • Konferensbidrag (refereegranskat)abstract
    • Experimental investigations showed passivation of the p-type dopants B and Al in 4H-SiC by the formation of B+H and Al+H complexes. The dissociation energies of these complexes differed by 0.9 eV. Ab initio supercell calculations have been performed to investigate the interaction of H with B and Al in hexagonal 4H-SiC. The total energy, geometry and electronic structure of the possible complexes have been determined. Site dependencies have also been investigated. The most stable configurations were found with H at a bond center site next to B at the Si site, and with H at the antibonding site of a carbon atom which is first neighbor to Al at a Si site. Both the BSi+HBC and the AlSi+HAB(C) complexes turned out to be electrically inactive. The different structure of the passivated complexes explains the observed difference in their dissociation energy: the calculated difference of the binding energies of these complexes is 0.9 eV, which agrees well with the experimental finding. © 2001 Elsevier Science B.V. All rights reserved.
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4.
  • Deak, P, et al. (författare)
  • A cause for SiC/SiO2 interface states : The site selection of oxygen in SiC
  • 2003
  • Ingår i: Materials Science Forum, Vols. 433-436. ; s. 535-538
  • Konferensbidrag (refereegranskat)abstract
    • We show that in the SiC/SiO2 system the interface states in the lower half of the gap are the consequence of the behavior of oxygen in SiC. Investigating the elemental steps of oxidation on a simple model by means of ab initio density functional calculations we find that, in course of the oxidation, carbon-vacancy (V-C) - oxygen complexes constantly arise. The V-C+O complexes have donor states around E-V+0.8 eV. Their presence gives rise to a thin transition layer which is not SiO2 but an oxygen contaminated Si-rich interface layer producing the aforementioned gap states.
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5.
  • Deak, Peter, et al. (författare)
  • Accurate defect levels obtained from the HSE06 range-separated hybrid functional
  • 2010
  • Ingår i: PHYSICAL REVIEW B. - American Physical Society. - 1098-0121. ; 81:15, s. 153203
  • Tidskriftsartikel (refereegranskat)abstract
    • Defect levels are a problem for standard implementations of density-functional theory and the error also influences the energetics. We demonstrate that the HSE06 functional, which describes the electronic structure of all group-IV semiconductors well (including Ge), gives highly accurate charge transition levels, too, if the defect wave function is host related-independent of localization. The degree of fulfilling the generalized Koopmans theorem shows the reliability of the results and the highest-occupied eigenvalue always seems to give the correct vertical ionization energy.
6.
  • Deak, P, et al. (författare)
  • Vacancies and their complexes with H in SiC
  • 2000
  • Ingår i: Materials Science Forum, Vols. 338-343. ; s. 817-820
  • Konferensbidrag (refereegranskat)abstract
    • Ab initio calculations (LDA and MCSF) have been carried out for vacancies (V-Si and V-C) and interstitial H, as well as for V+H complexes in 3C SiC. Relative stability of different charge-states/configurations and occupation levels were determined in supercells with plane wave basis sets while vibration frequencies and spin distributions were calculated in clusters with localized basis functions. Both types of vacancies show amphoteric electrical activity. In equilibrium, atomic He is at the AB(C), and H is at the T-Si site, while H-0 does not appear to be stable with respect to them, so H can also act both as a deep donor and an electron trap. Hydrogen can passivate the V-Si acceptor but not the V-C donor. Conditions for the formation of the possible V+H centers and their properties are given and used to discuss experimental information (or the lack of them) about H in SiC.
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7.
  • Falk, Abram L., et al. (författare)
  • Electrically and Mechanically Tunable Electron Spins in Silicon Carbide Color Centers
  • 2014
  • Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 112:18, s. 187601
  • Tidskriftsartikel (refereegranskat)abstract
    • The electron spins of semiconductor defects can have complex interactions with their host, particularly in polar materials like SiC where electrical and mechanical variables are intertwined. By combining pulsed spin resonance with ab initio simulations, we show that spin-spin interactions in 4H-SiC neutral divacancies give rise to spin states with a strong Stark effect, sub-10(-6) strain sensitivity, and highly spin-dependent photoluminescence with intensity contrasts of 15%-36%. These results establish SiC color centers as compelling systems for sensing nanoscale electric and strain fields.
8.
  • Gali, Adam, et al. (författare)
  • Aggregation of carbon interstitials in silicon carbide : A theoretical study
  • 2003
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 68:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Ab initio supercell calculations have been carried out to investigate clusters of carbon interstitials in 3C- and 4H-SiC. Based on the calculated formation energies, the complex formation of carbon interstitials or their aggregation to carbon antisites is energetically favored in SiC. The electronic and vibronic properties of the carbon interstitials and their aggregates depends strongly on the polytype. Using the calculated hyperfine constants and local vibrational modes of carbon clusters the possible relation to known carbon-related centers will be discussed.
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9.
  • Gali, Adam, et al. (författare)
  • Anti-site pair in SiC : A model of the DI center
  • 2003
  • Ingår i: Physica B. ; s. 175-179
  • Konferensbidrag (refereegranskat)abstract
    • The DI low-temperature photoluminescence center is a well-known defect stable up to 1700°C annealing in SiC, still its structure is not known after decades of study. Combining experimental and theoretical studies in this paper we will show that the properties of an anti-site pair can reproduce the measured one-electron level position and local vibration modes of the D I center and the model is consistent with other experimental findings as well. We give theoretical values of the hyperfine constants of the anti-site pair in its paramagnetic state as a means to confirm our model. © 2003 Elsevier B.V. All rights reserved.
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10.
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