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Träfflista för sökning "WFRF:(Gali Adam) "

Sökning: WFRF:(Gali Adam)

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  • 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.
  • 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.
  • 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.
  • Christle, David J., et al. (författare)
  • Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface
  • 2017
  • Ingår i: Physical Review X. - AMER PHYSICAL SOC. - 2160-3308. ; 7:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a high-fidelity spin-photon interface, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here, we demonstrate that such an interface exists in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have a millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on Si shows promise for future quantum networks based on SiC defects.
  • Davidsson, Joel, et al. (författare)
  • First principles predictions of magneto-optical data for semiconductor point defect identification: the case of divacancy defects in 4H-SiC
  • 2018
  • Ingår i: New Journal of Physics. - IOP PUBLISHING LTD. - 1367-2630. ; 20
  • Tidskriftsartikel (refereegranskat)abstract
    • Study and design of magneto-optically active single point defects in semiconductors are rapidly growing fields due to their potential in quantum bit (qubit) and single photon emitter applications. Detailed understanding of the properties of candidate defects is essential for these applications, and requires the identification of the defects microscopic configuration and electronic structure. In multicomponent semiconductors point defects often exhibit several non-equivalent configurations of similar but different characteristics. The most relevant example of such point defect is the divacancy in silicon carbide, where some of the non-equivalent configurations implement room temperature qubits. Here, we identify four different configurations of the divacancy in 4H-SiC via the comparison of experimental measurements and results of first-principle calculations. In order to accomplish this challenging task, we carry out an exhaustive numerical accuracy investigation of zero-phonon line and hyperfine coupling parameter calculations. Based on these results, we discuss the possibility of systematic quantum bit search.
  • 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.
  • 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.
  • Deak, P, et al. (författare)
  • Vacancies and their complexes with H in SiC
  • 2000
  • Ingår i: Materials Science Forum, Vols. 338-343. - Stafa-Zurich, Switzerland : Trans Tech Publications Inc.. ; 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.
  • 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.
  • Falk, Abram L., et al. (författare)
  • Optical Polarization of Nuclear Spins in Silicon Carbide
  • 2015
  • Ingår i: Physical Review Letters. - American Physical Society. - 0031-9007. ; 114:24, s. 247603
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate optically pumped dynamic nuclear polarization of Si-29 nuclear spins that are strongly coupled to paramagnetic color centers in 4H- and 6H-SiC. The 99% +/- 1% degree of polarization that we observe at room temperature corresponds to an effective nuclear temperature of 5 mu K. By combining ab initio theory with the experimental identification of the color centers optically excited states, we quantitatively model how the polarization derives from hyperfine-mediated level anticrossings. These results lay a foundation for SiC-based quantum memories, nuclear gyroscopes, and hyperpolarized probes for magnetic resonance imaging.
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