| 11. |
- Deak, P, et al.
(författare)
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A cause for SiC/SiO2 interface states : The site selection of oxygen in SiC
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. ; , s. 535-538
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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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| 12. |
- Deak, Peter, et al.
(författare)
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Accurate defect levels obtained from the HSE06 range-separated hybrid functional
- 2010
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Ingår i: PHYSICAL REVIEW B. - : American Physical Society. - 1098-0121. ; 81:15, s. 153203-
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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.
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| 13. |
- Deak, P, et al.
(författare)
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Vacancies and their complexes with H in SiC
- 2000
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Ingår i: Materials Science Forum, Vols. 338-343. - Stafa-Zurich, Switzerland : Trans Tech Publications Inc.. ; , s. 817-820
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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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| 14. |
- Dhungel, Omkar, et al.
(författare)
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Near zero-field microwave-free magnetometry with ensembles of nitrogen-vacancy centers in diamond
- 2024
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 109:22
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Tidskriftsartikel (refereegranskat)abstract
- We study cross -relaxation features near zero magnetic field with ensembles of nitrogen -vacancy (NV) centers in diamond and examine their properties in samples with a range of 0.9-16.0 ppm of NV concentrations. The observed NV -NV cross -relaxation features between differently oriented NV centers in high (>= 0.9 ppm)NV-density samples hold promise for a variety of magnetometry applications where microwave fields (or any bias field) disturb the system under study. We theoretically determine the values of the bias magnetic fields corresponding to cross relaxations between different axes and experimentally validate them. The behavior of zero -field cross -relaxation features as a function of temperature is also investigated.
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| 15. |
- Falk, Abram L., et al.
(författare)
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Electrically and Mechanically Tunable Electron Spins in Silicon Carbide Color Centers
- 2014
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 112:18, s. 187601-
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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.
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| 16. |
- Falk, Abram L., et al.
(författare)
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Optical Polarization of Nuclear Spins in Silicon Carbide
- 2015
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 114:24, s. 247603-
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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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| 17. |
- Gali, Adam, et al.
(författare)
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Aggregation of carbon interstitials in silicon carbide : A theoretical study
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:12
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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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| 18. |
- Gali, Adam, et al.
(författare)
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Anti-site pair in SiC : A model of the DI center
- 2003
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Ingår i: Physica B. - : Elsevier BV. ; , s. 175-179
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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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| 19. |
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| 20. |
- Gali, Adam, et al.
(författare)
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Calculation of hyperfine constants of defects in 4H-SiC
- 2003
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Ingår i: Materials Science Forum, Vols. 433-436. ; , s. 511-514
-
Konferensbidrag (refereegranskat)abstract
- Knowledge about the creation and diffusion of intrinsic point defects is crucial for devising annealing strategies after irradiation steps as, e.g., implantation. Experimental information can be obtained by observing the appearance and/or disappearance of characteristic electrical, optical or magnetic spectra, however, these have to be first assigned to a given defect. In case of silicon carbide even this very first task has not been accomplished yet in case of the carbon vacancy, with which two different electron spin resonance (ESR) centers (anneling out at very different temperatures) have been identified. Ab initio all-electron supercell calculations have been carried out to determine the hyperfine constants of several defects in 4H-SiC in order to justify the models of the measured ESR signals. The quality of the results were tested on the well-documented case of interstitial hydrogen in silicon.
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