| 1. |
- Aradi, B, et al.
(författare)
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Boron centers in 4H-SiC
- 2001
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Ingår i: Materials science Forum, Vols. 353-356. ; , s. 455-458
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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)
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Impurity-controlled dopant activation - The role of hydrogen in p-type doping of SiC
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 561-564
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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)
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Passivation of p-type dopants in 4H-SiC by hydrogen
- 2001
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Ingår i: Physica B, Vols. 308-310. ; , s. 722-725
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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. |
- Barcza, Gergely, et al.
(författare)
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DMRG on Top of Plane-Wave Kohn-Sham Orbitals: A Case Study of Defected Boron Nitride
- 2021
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Ingår i: Journal of Chemical Theory and Computation. - : AMER CHEMICAL SOC. - 1549-9618 .- 1549-9626. ; 17:2, s. 1143-1154
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we analyze the numerical aspects of the inherent multireference density matrix renormalization group (DMRG) calculations on top of the periodic Kohn-Sham density functional theory using the complete active space approach. The potential of the framework is illustrated by studying hexagonal boron nitride nanoflakes embedding a charged single boron vacancy point defect by revealing a vertical energy spectrum with a prominent multireference character. We investigate the consistency of the DMRG energy spectrum from the perspective of sample size, basis size, and active space selection protocol. Results obtained from standard quantum chemical atom-centered basis calculations and plane-wave based counterparts show excellent agreement. Furthermore, we also discuss the spectrum of the periodic sheet which is in good agreement with extrapolated data of finite clusters. These results pave the way toward applying the DMRG method in extended correlated solid-state systems, such as point defect qubit in wide band gap semiconductors.
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| 5. |
- Christle, David J., et al.
(författare)
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Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface
- 2017
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Ingår i: Physical Review X. - : AMER PHYSICAL SOC. - 2160-3308. ; 7:2
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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.
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| 6. |
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| 7. |
- Davidsson, Joel, et al.
(författare)
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First principles predictions of magneto-optical data for semiconductor point defect identification: the case of divacancy defects in 4H-SiC
- 2018
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Ingår i: New Journal of Physics. - : IOP PUBLISHING LTD. - 1367-2630. ; 20
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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.
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| 8. |
- Davidsson, Joel, et al.
(författare)
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Identification of divacancy and silicon vacancy qubits in 6H-SiC
- 2019
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 114:11
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Tidskriftsartikel (refereegranskat)abstract
- Point defects in semiconductors are relevant for use in quantum technologies as room temperature qubits and single photon emitters. Among suggested defects for these applications are the negatively charged silicon vacancy and the neutral divacancy in SiC. The possible nonequivalent configurations of these defects have been identified in 4H-SiC, but for 6H-SiC, the work is still in progress. In this paper, we identify the different configurations of the silicon vacancy and the divacancy defects to each of the V1-V3 and the QL1-QL6 color centers in 6H-SiC, respectively. We accomplish this by comparing the results from ab initio calculations with experimental measurements for the zero-phonon line, hyperfine tensor, and zero-field splitting. Published under license by AIP Publishing.
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| 9. |
- 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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| 10. |
- 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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