| 1. |
- Blumenau, A.T., et al.
(author)
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The effect of charge on kink migration at 90° partial dislocations in SiC
- 2005
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In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:5, s. 877-882
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Journal article (peer-reviewed)abstract
- SiC bipolar devices show a degradation under forward-biased operation which has been linked with a recombination enhanced motion of one of the two glide dislocations having either Si or C core atoms. We have carried out calculations of the core structures and dynamics of partial dislocations in 3C and 2H-SiC using the density functional based codes DFTB and AIMPRO. After in earlier theoretical work we reported on the structure, energetics and electronic activity of both of the Shockley partials, and on the formation and migration barriers of kinks, in this work we present first results on the effect of charge on the disloction kinks. The calculations give insights into the device degradation mechanism.
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| 2. |
- Goss, J.P., et al.
(author)
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Planar interstitial aggregates in Si
- 2002
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:48, s. 12843-12853
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Journal article (peer-reviewed)abstract
- Self-interstitials in silicon aggregate to form rod-like defects aligned along [110] directions and inhabiting either {111} or {113} crystallographic planes. These systems are known to be electrically and optically active. We present the results of first-principles calculations on the structure and energetics for candidate structures contained within the {113}, {111} and {001} planes and compare the results with experiment.
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| 3. |
- Schlenk, T., et al.
(author)
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Controllable Magnetic Doping of the Surface State of a Topological Insulator
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:12, s. 126804-
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Journal article (peer-reviewed)abstract
- A combined experimental and theoretical study of doping individual Fe atoms into Bi2Se3 is presented. It is shown through a scanning tunneling microscopy study that single Fe atoms initially located at hollow sites on top of the surface (adatoms) can be incorporated into subsurface layers by thermally activated diffusion. Angle-resolved photoemission spectroscopy in combination with ab initio calculations suggest that the doping behavior changes from electron donation for the Fe adatom to neutral or electron acceptance for Fe incorporated into substitutional Bi sites. According to first principles calculations within density functional theory, these Fe substitutional impurities retain a large magnetic moment, thus presenting an alternative scheme for magnetically doping the topological surface state. For both types of Fe doping, we see no indication of a gap at the Dirac point. DOI: 10.1103/PhysRevLett.110.126804
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| 4. |
- Blumenau, A.T., et al.
(author)
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Basal plane partial dislocations in silicon carbide
- 2003
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In: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 340, s. 160-164
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Journal article (peer-reviewed)abstract
- Under operating conditions (forward bias) bipolar 4H- and 6H-SiC devices are known to degrade rapidly through stacking fault formation and expansion in the basal plane. It has been suggested that a recombination-enhanced dislocation glide (REDG) mechanism allows the bordering Shockley partial dislocations to overcome their barrier to glide motion and thus results in the observed stacking fault growth. In this work, we investigate the structure and properties of the participating Shockley partials by means of density functional-based atomistic calculations. Their glide motion is modelled in a process involving the formation and subsequent migration of kinks. This in combination with an analysis of the electronic structure of the partials allows an identification of those types which will be affected by the REDG mechanism.
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| 5. |
- Blumenau, A.T., et al.
(author)
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Density functional based modelling of 30° partial dislocations in SiC
- 2004
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In: Proceedings of the 10th International Conference on Silicon Carbide and Related Materials, ICSCRM 2003. - Stafa-Zuerich : Trans Tech Publications Inc.. - 0878499431 ; , s. 453-456
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Conference paper (peer-reviewed)abstract
- Experiment has shown that 4H- and 6H-SiC pin diodes degrade rapidly during forward biased operation. This degradation is accompanied by the formation and expansion of stacking faults in the basal plane. It is believed that the observed rapid stacking fault growth is due to a recombination-enhanced dislocation glide (REDG) mechanism at the bordering partial dislocations. In our work we investigate the structure and properties of basal plane 30° Shockley partials in SiC by means of density functional based calculations. Barriers to their glide motion, and thus the expansion of the accompanying stacking fault is modelled in a process involving the formation and subsequent migration of kinks in the dislocation. In combination with an analysis of the electronic structure of the partials and stacking faults, this allows an identification of those types of partials which will be affected by the REDG mechanism in this model.
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| 6. |
- Blumenau, A. T., et al.
(author)
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Dislocation related photoluminescence in silicon
- 2001
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 87:18
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Journal article (peer-reviewed)abstract
- Dislocation related photoluminescence in Si and SiGe is attributed to stable interstitial clusters bound to 60° dislocations. Density functional based total energy calculations in Si give binding energies between 1.5 and 3.6 eV for I3 and I4 clusters with 90° and 30° partials. They possess donor levels around Ev+0.4 eV which are consistent with deep level transient spectroscopic studies on p-Si. It is further suggested that the clusters would act as the obstacles to the movement of dislocations which may have been observed in recent transmission electron microscopy studies.
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| 7. |
- Blumenau, A.T., et al.
(author)
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Dislocations in hexagonal and cubic GaN
- 2000
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12, s. 10223-10233
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Journal article (peer-reviewed)abstract
- The structure and electronic activity of several types of dislocations in both hexagonal and cubic GaN are calculated using first-principles methods. Most of the stoichiometric dislocations investigated in hexagonal GaN do not induce deep acceptor states and thus cannot be responsible for the yellow luminescence. However, it is shown that electrically active point defects, in particular gallium vacancies and oxygen-related defect complexes, can be trapped at the stress field of the dislocations and may be responsible for this luminescence. For cubic GaN, we find the ideal stoichiometric 60° dislocation to be electrically active and the glide set to be more stable than the shuffle. The dissociation of the latter is considered
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| 8. |
- Blumenau, A.T., et al.
(author)
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Optical bands related to dislocations in Si
- 2000
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:49, s. 10123-10129
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Journal article (peer-reviewed)abstract
- First-principles calculations are used to investigate the interaction of self-interstitial aggregates with the 90° partial dislocation in Si. We find that I4 is bound to the line with an energy of around 3 eV. The defect causes deep levels to appear in the band gap and optical transitions between these levels may account for the luminescent bands relating to plastically deformed Si.
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| 9. |
- Blumenau, A.T., et al.
(author)
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Straight and kinked 90° partial dislocations in diamond and 3C-SiC
- 2002
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:48, s. 12741-12747
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Journal article (peer-reviewed)abstract
- Density-functional based calculations are used to investigate low energy core structures of 90° partial dislocations in diamond and 3C-SiC. In both materials dislocation glide is analysed in terms of kink formation and migration and the fundamental steps to kink migration are investigated. We find the C terminated core structure in SiC to be more mobile than the Si core. However, the Si partial is electrically active and this opens the possibility of recombination-enhanced glide under ionizing conditions or an enhanced mobility in doped material.
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| 10. |
- Blumenau, A.T., et al.
(author)
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Structure and motion of basal dislocations in silicon carbide
- 2003
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:17, s. 174108-1
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Journal article (peer-reviewed)abstract
- 30° and 90° Shockley partial dislocations lying in {111} and basal planes of cubic and hexagonal silicon carbide, respectively, are investigated theoretically. Density-functional-based tight-binding total-energy calculations are used to determine the core structure and energetics of the dislocations. In a second step their electronic structure is investigated using a pseudopotential method with a Gaussian basis set. Finally, the thermal activation barriers to glide motion of 30° and 90° Shockley partials are calculated in terms of a process involving the formation and migration of kinks along the dislocation line. The mechanism for enhanced dislocation movement observed under current injection conditions in bipolar silicon carbide devices is discussed.
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| 11. |
- van der Heide, T., et al.
(author)
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Fortnet, a software package for training Behler-Parrinello neural networks
- 2023
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In: Computer Physics Communications. - : Elsevier. - 0010-4655 .- 1879-2944. ; 284
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Journal article (peer-reviewed)abstract
- A new, open source, parallel, stand-alone software package (Fortnet) has been developed, which implements Behler-Parrinello neural networks. It covers the entire workflow from feature generation to the evaluation of generated potentials, coupled with higher-level analysis such as the analytic calculation of atomic forces. The functionality of the software package is demonstrated by driving the training for the fitted correction functions of the density functional tight binding (DFTB) method, which are commonly used to compensate the inaccuracies resulting from the DFTB approximations to the Kohn -Sham Hamiltonian. The usual two-body form of those correction functions limits the transferability of the parametrizations between very different structural environments. The recently introduced DFTB+ANN approach strives to lift these limitations by combining DFTB with a near-sighted artificial neural network (ANN). After investigating various approaches, we have found the combination of DFTB with an ANN acting on-top of some baseline correction functions (delta learning) the most accurate one. It allowed to introduce many-body corrections on top of two-body parametrizations, while excellent transferability to chemical environments with deviating energetics could be demonstrated.
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| 12. |
- Aradi, B, et al.
(author)
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Boron centers in 4H-SiC
- 2001
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In: Materials science Forum, Vols. 353-356. ; , s. 455-458
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Conference paper (peer-reviewed)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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| 13. |
- Blumenau, AT, et al.
(author)
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Dislocation structures in diamond : density-functional based modelling and high-resolution electron microscopy
- 2004
-
In: Defect and Diffusion Forum. - Zürich : Trans Tech Publications. - 1012-0386 .- 1662-9507. ; 226-228, s. 11-30
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Journal article (peer-reviewed)abstract
- The core structures of perfect 60 and edge dislocations in diamond are investigated atomistically in a density-functional based tight-binding approach, and their dissociation is discussed both in terms of structure and energy. Furthermore, high resolution electron microscopy is performed on dislocation cores in high-temperature, high-pressure annealed natural brown diamond, and HRTEM image simulation allows a comparison of theoretically predicted and experimentally observed structures.
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| 14. |
- Deak, P, et al.
(author)
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A cause for SiC/SiO2 interface states : The site selection of oxygen in SiC
- 2003
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In: Materials Science Forum, Vols. 433-436. ; , s. 535-538
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Conference paper (peer-reviewed)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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| 15. |
- Fujita, N., et al.
(author)
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Diffusion of nitrogen in silicon
- 2005
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:2, s. 21902-
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Journal article (peer-reviewed)abstract
- We use local density functional theory to investigate the diffusion of nitrogen dimers in silicon. We investigate several trajectories for the diffusing dimer finding an alternative one whose barrier is 2.69 eV and in close agreement with experimental diffusion data carried out at high temperature. We suggest that recent reports of a low barrier of 1.45 eV found from studies of dislocation unlocking are to be understood from the interaction of nitrogen dimers with interstitials or vacancies released by the dislocation.
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| 16. |
- Fujita, N., et al.
(author)
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Theoretical investigations of the diffusion of nitrogen-pair defects in silicon
- 2005
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In: Solid State Phenomena. - 1012-0394 .- 1662-9779. ; 108, s. 407-12
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Journal article (peer-reviewed)abstract
- The formation of oxygen precipitates and microvoids as well as the movement and growth of dislocations are strongly affected by the presence of nitrogen. However, the diffusion mechanism of nitrogen is unclear with several conflicting reports in the literature. Here, ab initio density functional theory is used to investigate diffusion mechanisms of the nitrogen-pair defect in silicon. We find a new metastable nitrogen-pair defect structure, which is lower in energy than any structures previously considered as intermediate structures in the minimum energy paths. Thus, by including this new metastable structure, we suggest a more likely, alternative reaction path whose barrier is 2.69 eV. This is compared with experimental barriers
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| 17. |
- Hourahine, B., et al.
(author)
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Germanium-hydrogen pairs in silicon
- 2003
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 15:39, s. S2803-S2807
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Journal article (peer-reviewed)abstract
- Hydrogen in a dilute SiGe alloy is considered theoretically in comparison with hydrogen in Si and Ge. Structural, vibrational and electronic properties of crystalline alloys containing ~1.6 at.% Ge complexed with single hydrogen atoms are considered. The behaviour of bond-centred hydrogen is found to be weakly perturbed, when compared to hydrogen in pure Si.
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| 18. |
- Hourahine, B., et al.
(author)
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Platinum and gold dihydrides in silicon
- 2003
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In: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 340, s. 668-72
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Journal article (peer-reviewed)abstract
- The structural, electronic and vibrational properties of single substitutional platinum or gold atoms complexed with two hydrogen atoms in silicon are considered on the basis of local density functional theory. The calculated behaviour of these centres is compared with experimental results from infrared absorption and deep-level transient spectroscopy. In contrast with suggestions in the literature, based on hyperfine parameters of electron-paramagnetic resonance, we suggest that such complexes possess direct metal-H bonding.
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