| 1. |
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| 2. |
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Bruzzi, M, et al.
(författare)
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Radiation-hard semiconductor detectors for SuperLHC
- 2005
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 541:1-2, s. 189-201
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Tidskriftsartikel (refereegranskat)abstract
- An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Goss, J.P., et al.
(författare)
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First principles studies of H in diamond
- 2001
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 186:2, s. 263-8
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio methods are used to investigate hydrogen defects in diamond. For the isolated impurity, the bond-centered site is found lowest in energy and posses both donor and acceptor levels. The neutral defect possesses a single local mode with very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H*2 defects which are also found to be almost IR-inactive. The complex between B and H is investigated and the activation energy for the reaction B-H → B - + H+ found to be in rasonable agreement with experiment. Hydrogen is strongly bound to dislocations which, together with H*2, may form part of the hydrogen accumulation layer detected in some plasma studies.
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| 11. |
- Goss, J. P., et al.
(författare)
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Theory of hydrogen in diamond
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:11
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio cluster and supercell methods are used to investigate the local geometry and optical properties of hydrogen defects in diamond. For an isolated impurity, the bond-centered site is found to be lowest in energy, and to possess both donor and acceptor levels. The neutral defect possesses a single local mode with a very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H2* defects, which are also found to be almost IR inactive. The complex between B and H is investigated and the activation energy for the reaction B-H→B-+H+ found to be around 1.8 eV in agreement with experiment. We also investigate complexes of hydrogen with phosphorus and nitrogen. The binding energy of H with P is too low to lead to a significant codoping effect. A hydrogen-related vibrational mode of the N-H defect, and its isotopic shifts, are close to the commonly observed 3107-cm-1 line, and we tentatively assign this center to the defect. Hydrogen is strongly bound to dislocations which, together with H2*, may form part of the hydrogen accumulation layer detected in some plasma studies.
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| 12. |
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| 13. |
- Reed, B. P., et al.
(författare)
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Diamond (111) surface reconstruction and epitaxial graphene interface
- 2022
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Ingår i: Physical Review B. - 2469-9950. ; 105:20
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the diamond (111) surface as it undergoes reconstruction and subsequent graphene formation is investigated with angle-resolved photoemission spectroscopy, low energy electron diffraction, and complementary density functional theory calculations. The process is examined starting at the C(111)-(2×1) surface reconstruction that occurs following detachment of the surface adatoms at 920 ∘C, and continues through to the liberation of the reconstructed surface atoms into a freestanding monolayer of epitaxial graphene at temperatures above 1000 ∘C. Our results show that the C(111)-(2×1) surface is metallic as it has electronic states that intersect the Fermi level. This is in strong agreement with a symmetrically π-bonded chain model and should contribute to resolving the controversies that exist in the literature surrounding the electronic nature of this surface. The graphene formed at higher temperatures exists above a newly formed C(111)-(2×1) surface and appears to have little substrate interaction as the Dirac point is observed at the Fermi level. Finally, we demonstrate that it is possible to hydrogen-terminate the underlying diamond surface by means of plasma processing without removing the graphene layer, forming a graphene-semiconductor interface. This could have particular relevance for doping the graphene formed on the diamond (111) surface via tuneable substrate interactions as a result of changing the terminating species at the diamond-graphene interface by plasma processing.
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| 14. |
- Al-Hamadandy, Raied, et al.
(författare)
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Oxygen vacancy migration in compressively strained SrTiO3
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:2
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Tidskriftsartikel (refereegranskat)abstract
- The intrinsic properties of strontium titanate render it promising in applications such as gate dielectrics and capacitors. However, there is growing evidence that oxygen vacancies significantly impact upon its use, with the diffusion and deep donor level of the oxygen vacancy leading to electrical leakage. Where grown epitaxially on a lattice mismatched substrate, SrTiO 3 undergoes bi-axial strain, altering its crystal structure and electronic properties. In this paper, we present the results of first-principles simulations to evaluate the impact of strain in a (001) plane upon the migration of oxygen vacancies. We show that in the range of strains consistent with common substrate materials, diffusion energies in different directions are significantly affected, and for high values of strain may be altered by as much as a factor of two. The resulting diffusion anisotropy is expected to impact upon the rate at which oxygen vacancies are injected into the films under bias, a critical factor in the leakage and resistive switching seen in this material
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| 15. |
- Al-Hamadany, R., et al.
(författare)
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Impact of tensile strain on the oxygen vacancy migration in SrTiO3 : Density functional theory calculations
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:22
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Tidskriftsartikel (refereegranskat)abstract
- Strontium titanate is a promising dielectric material for device applications including capacitors and gate dielectrics. However, oxygen vacancies, which are inevitable donor defects mobile under bias at room temperature, lead to undesirable leakage current in SrTiO3 thin films. Epitaxially grown SrTiO3 on lattice mismatched substrates leads to strained SrTiO3, inducing structural phase transitions from a cubosymmetric non-ferroelectric geometry to tetragonal and orthorhombic structures, depending upon the sign of the strain. In this study, density functional calculations have been performed to determine the impact of isotropic biaxial tensile strain in a (001) plane upon the phase of SrTiO3 and the activation energy for the migration of oxygen vacancies in such strained SrTiO3. The phase transition of the host material yields anisotropy in oxygen vacancy diffusion for diffusion within and between planes parallel to the strain. We found a general reduction in the barrier for diffusion within and normal to the plane of tensile strain. The inter-plane diffusion barrier reduces up to 25% at high values of strain. The variation in the barrier corresponding to in-plane diffusion is smaller in comparison to inter-plane diffusion. Finally, we reflect upon how the interplay between lattice strain with native defects plays a crucial role in the conduction mechanism of thin film, strained SrTiO3
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| 16. |
- Atumi, M.K., et al.
(författare)
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Hyperfine interaction of H-divacancy in diamond
- 2020
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Ingår i: Results in Physics. - : Elsevier. - 2211-3797. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- We present a first principles density functional theory study of microscopic properties of hydrogen defect centres in diamond. Several configurations, involving interstitial hydrogen impurities, have been considered either forming with other defects, such as hydrogen defects and vacancies. The atomic structures, and hyperfine parameters of hydrogen result compared with the experimental data on electrically active centres in synthetic diamond. Based on Local density functional theory our calculations are in excellent agreement with one interpretation of electron paramagnetic resonance of hydrogen in diamond.
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| 17. |
- Atumi, M.K., et al.
(författare)
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Hyperfine interactions at nitrogen interstitial defects in diamond
- 2013
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:6
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Tidskriftsartikel (refereegranskat)abstract
- Diamond has many extreme physical properties and it can be used in a wide range of applications. In particular it is a highly effective particle detection material, where radiation damage is an important consideration. The WAR9 and WAR10 are electron paramagnetic resonance centres seen in irradiated, nitrogen-containing diamond. These S = 1/2 defects have C2v and C1h symmetry, respectively, and the experimental spectra have been interpreted as arising from nitrogen split-interstitial centres. Based upon the experimental and theoretical understanding of interstitial nitrogen defect structures, the AIMPRO density functional code has been used to assess the assignments for the structures of WAR9 and WAR10. Although the calculated hyperfine interaction tensors are consistent with the measured values for WAR9, the thermal stability renders the assignment problematic. The model for the WAR10 centre yields principal directions of the hyperfine tensor at variance with observation. Alternative models for both centres are discussed in this paper, but no convincing structures have been found.
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| 18. |
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| 19. |
- Budde, M., et al.
(författare)
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Identification of the hydrogen-saturated self-interstitials in silicon and germanium
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:18, s. 4397-4412
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Tidskriftsartikel (refereegranskat)abstract
- Silicon and germanium single crystals are implanted with protons. The infrared-absorption spectra of the samples contain sharp absorption lines due to the excitation of hydrogen-related local vibrational modes. The lines at 743.1, 748.0, 1986.5, and 1989.4 cm-1 in silicon and at 700.3, 705.5, 1881.8, and 1883.5 cm-1 in germanium originate from the same defect in the two materials. Measurements on samples coimplanted with protons and deuterons show that the defect contains two equivalent hydrogen atoms. Uniaxial stress measurements are carried out and a detailed analysis of the results is presented. It is shown that the defect has monoclinic-II symmetry, and the orientations of the Si-H and Ge-H bonds of the defect are determined. Ab initio local-density-functional theory is used to calculate the structure and local vibrational modes of the self-interstitial binding one and two hydrogen atoms in silicon and germanium together with the structure of the self-interstitial itself. The observed properties of the defect are in excellent agreement with those calculated for the self-interstitial binding two hydrogen atoms.
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| 20. |
- Budde, M., et al.
(författare)
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The hydrogen-saturated self-interstitial in silicon and germanium
- 1997
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Ingår i: Defects in semiconductors. - : Trans Tech Publications Inc.. ; , s. 35-40
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Konferensbidrag (refereegranskat)abstract
- Infrared absorption spectroscopy is used to study H-related point defects in H+-implanted Si (Si:H) and Ge (Ge:H). The absorption lines at 743.1, 748.0, 1986.5 and 1989.4 cm-1 in Si:H and at 700.3, 705.5, 1881.8 and 1883.5 cm-1 in Ge:H are shown to originate from the same defect containing two equivalent H atoms. Uniaxial stress experiments show that the defects have monoclinic-II symmetry, and the orientations of the two Si-H or Ge-H bonds are determined. The structure and the local vibrational modes of the self-interstitial binding two H atoms (IH2) are calculated with LDF cluster theory. The symmetry, bond-orientations and isotopic frequency-shifts calculated for IH2 are in excellent agreement with those observed for the 743.1-, 748.0-, 1986.5- and 1989.4-cm-1 modes in Si:H and for the 700.3-, 705.5-, 1881.8- and 1883.5-cm-1 modes in Ge:H.
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| 21. |
- Carvalho, A, et al.
(författare)
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First-principles study of the diffusion mechanisms of the self-interstitial in germanium
- 2008
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:13
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Tidskriftsartikel (refereegranskat)abstract
- The self-interstitial in germanium can assume multiple configurations depending on the temperature and charge state. Here, we employ a first-principles density functional method to investigate the diffusion mechanisms of this defect. The energy barriers associated with the transformation between different structures are determined by the climbing nudged elastic band method, as a function of the charge state. The relation between the thermodynamic properties of the self-interstitial and the temperature evolution of electron radiation damage in germanium are discussed.
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| 22. |
- Carvalho, A., et al.
(författare)
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Self-interstitial in germanium
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:17, s. 175502-
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature radiation damage in n- and p-type Ge is strikingly different, reflecting the charge-dependent properties of vacancies and self-interstitials. We find, using density functional theory, that in Ge the interstitial is bistable, preferring a split configuration when neutral and an open cage configuration when positively charged. The split configuration is inert while the cage configuration acts as a double donor. We evaluate the migration energies of the defects and show that the theory is able to explain the principal results of low-temperature electron-irradiation experiments.
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| 23. |
- Coomer, B.J., et al.
(författare)
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Identification of the tetra-interstitial in silicon
- 2001
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:1, s. L1-L7
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Tidskriftsartikel (refereegranskat)abstract
- First-principles computational methods are employed to investigate the structural, vibrational, optical and electronic properties of the self-interstitial aggregate, I4 in silicon. We find the defect to be electrically active and identify it with the B3 EPR centre. We also show that its properties are consistent with DLTS and optical spectra observed following implantation of silicon.
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| 24. |
- Coomer, B.J., et al.
(författare)
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Interstitial aggregates and a new model for the I1/W optical centre in silicon
- 1999
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 505-508
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Tidskriftsartikel (refereegranskat)abstract
- The properties of di-interstitial (I2), tri-interstitial (I3) and tetra-interstitial (I4) structures in silicon were studied by employing first principles local-density-functional (LDF) theory. A tri-interstitial defect can account for many of the fundamental properties of the I1/W-optical center which is observed in irradiated, annealed silicon. Energy comparisons between di-interstitial defects reveal four low-energy structures within 0.5 eV of each other.
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| 25. |
- Coomer, B.J., et al.
(författare)
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The divacancy in silicon and diamond
- 1999
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 520-523
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Tidskriftsartikel (refereegranskat)abstract
- First-principles studies of the divacancy (V2) in both silicon and diamond are reported. We demonstrate that the contrasting experimental spin-density localisation of both systems can be explained through the one-electron pictures arising from opposing distortions
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| 26. |
- Eberlein, T.A.G., et al.
(författare)
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Self-interstitial clusters in silicon
- 2001
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308-310, s. 454-457
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Tidskriftsartikel (refereegranskat)abstract
- Although there have been made many calculations for structures of the self-interstitial in Si and small aggregates of interstitials, In, there have been relatively few attempts to relate these defects with experimental data. Here, we discuss the assignments of the self-interstitial to the AA12 EPR centre and the di-interstitial to the P6 EPR centre.
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| 27. |
- Fujita, N., et al.
(författare)
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Diffusion of nitrogen in silicon
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:2, s. 21902-
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Tidskriftsartikel (refereegranskat)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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| 28. |
- Fujita, N., et al.
(författare)
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Theoretical investigations of the diffusion of nitrogen-pair defects in silicon
- 2005
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Ingår i: Solid State Phenomena. - 1012-0394 .- 1662-9779. ; 108, s. 407-12
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Tidskriftsartikel (refereegranskat)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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| 29. |
- Goss, J.P., et al.
(författare)
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A first principles study of interstitial Si in diamond
- 1997
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Ingår i: Defects in Semiconductors. - : Trans Tech Publications Inc.. ; , s. 781-786
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The results of first principles calculations using AIMPRO (a local-density-functional code) are presented to describe the stability of interstitial Si in diamond. It is found that the 〈100〉 and 〈110〉 split-interstitial configurations are only local minima in the total energy surface. Td interstitial Si reconstructs to form a substitutional Si site close to a self-interstitial. The difference in total energy between the split configuration and the substitutional-Si-self-interstitial complex is more than 6 eV. It is concluded that Si would not adopt an interstitial location in diamond as has been previously suggested from experimental evidence. Interestingly the self-interstitial remains bound to the substitutional Si with a binding energy around 1 eV.
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| 30. |
- Goss, J.P., et al.
(författare)
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(CAs)2-hydrogen defects in GaAs : a first-principles study
- 1997
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 55:23, s. 15576-15580
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-related local vibrational modes at 2643, 2651, 2688, 2725, 2729, and 2775 cm-1 are thought to arise from C-H stretch modes from defects similar to the hydrogen-passivated carbon acceptor complex CAsH. These lines appear in samples that are grown using trimethylgallium metalorganic precursors, and it has been suggested that the 2688-, 2725-, 2729-, and 2775-cm-1 bands may be due to CAs dimers decorated with one or more H atoms. We present here the structures, energies, and vibrational modes of (CAs)2, (CAs)2H, and (CAs)2H2 complexes obtained from ab initio local-density-functional cluster calculations to investigate these assignments.
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| 31. |
- Goss, J.P., et al.
(författare)
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Electrical and optical properties of rod-like defects in silicon
- 2004
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 85:20, s. 4633-4635
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Tidskriftsartikel (refereegranskat)abstract
- Self-interstitials in silicon can aggregate to form rod-like defects (RLDs) having both electrical and optical activity. We carry out local density functional calculations for both {113} and {111} RLDs to determine their structures and electrical activity. We find that small {113} RLDs are more stable than {111} RLDs but this reverses for larger defects. We attribute the electrical activity of {113} RLDs found in deep level transient spectroscopy studies with the bounding dislocations and the 0.903 eV photoluminescence to vacancy point defects lying on the habit plane.
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| 32. |
- Goss, J.P., et al.
(författare)
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Extended defects in diamond: the interstitial platelet
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:16, s. 165208-1
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Tidskriftsartikel (refereegranskat)abstract
- The structure and properties of the {001} planar platelet in diamond are investigated using ab initio theory. We find that a carbonaceous model, based on a layer of self-interstitials, satisfies the requirements of transmission electron microscopy, infrared absorption data, and energetic considerations. The energetics of self-interstitial production during nitrogen aggregation are considered. It is found that the growth mechanism of the platelet involves a thermally activated release of vacancies from platelets. The role of vacant sites and platelet nitrogen are also investigated and it is shown that these defects embedded within the platelet could account for the observed optical activity.
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| 33. |
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| 34. |
- Goss, J.P., et al.
(författare)
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Interstitial aggregates in diamond
- 2001
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Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 10:3, s. 434-438
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical modelling of magnetic resonance signals lead to convincing models for the first three self-interstitial aggregates in diamond. These in turn suggest the manner in which larger more stable aggregates including the platelet, observed in annealed type I diamonds, are formed.
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| 35. |
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| 36. |
- Goss, J.P., et al.
(författare)
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Planar interstitial aggregates in Si
- 2002
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:48, s. 12843-12853
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Tidskriftsartikel (refereegranskat)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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| 37. |
- Goss, J.P., et al.
(författare)
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Self-interstitial aggregation in diamond
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:19, s. 195208-
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Tidskriftsartikel (refereegranskat)abstract
- First-principles methods are used to investigate the self-interstitial and its aggregates in diamond. The experimental assignment of the spin-1 R2 EPR center to the single interstitial has been questioned because of the small fine-structure term observed. We calculate the spin-spin interaction tensor for the three interstitial defects I1〈001〉, I2NN, and I3 and compare with the experimental D tensors. The results give support for the assignments of the single and di-interstitials to microscopic models and allow us to conclusively identify a recently observed EPR center, O3, with I3. This identification, in turn, suggests a low-energy structure for I4 and a generic model for an extended defect called the platelet. We also determine the optical properties of I1〈001〉 as well as its piezospectroscopic or stress tensor and find these to be in agreement with experiment. Several multi-interstitial defects are found to possess different structural forms which may coexist. We propose that a different form of the charged I2 defect gives rise to the 3H optical peak. Several structures of the platelet are considered, and we find that the lowest-energy model is consistent with microscopic and infrared studies.
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| 38. |
- Goss, J.P., et al.
(författare)
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Small aggregates of interstitials and models for platelets in diamond
- 2000
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:49, s. 10257-10261
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Tidskriftsartikel (refereegranskat)abstract
- By examining the structure of small clusters of self-interstitials in diamond using local-density-functional techniques, we have developed models for the planar defects called platelets. We present the structures, energies and vibrational properties
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| 39. |
- Goss, J.P., et al.
(författare)
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The lattice location of Ni in diamond : a theoretical study
- 2004
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 16:25, s. 4567-4578
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Tidskriftsartikel (refereegranskat)abstract
- Experiment unambiguously shows substitutional nickel is present in as-grown synthetic diamond where Ni is present in the solvent-catalyst. There is less convincing evidence for the presence of an interstitial species. We present the results of first-principles calculations of the properties of substitutional and interstitial Ni in diamond. The formation energy and mobility of the interstitial species suggest that nickel will be predominantly of the substitutional form. We also present possible models for the trigonal 1.404 eV optical centre correlated with the NIRIM-2 paramagnetic defect.
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| 40. |
- Goss, J P, et al.
(författare)
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The twelve-line 1.682 eV luminescence center in diamond and the vacancy-silicon complex
- 1996
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 77:14, s. 3041-3044
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio cluster methods are used to investigate vacancy-impurity complexes in diamond. We assign the 1.682 eV, twelve-line optical band to a vacancy-Si complex which has a very unusual, possibly unique structure with a Si atom at the center of a split vacancy. The method also successfully accounts for the 1.945, 2.156, and 2.985 eV optical transitions in trigonal vacancy-N defects and estimates of radiative lifetimes are given.
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| 41. |
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| 42. |
- Goss, J.P., et al.
(författare)
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Vibrational modes and electronic properties of nitrogen defects in silicon
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:4, s. 45206-1
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen impurities form complexes with native defects such as vacancies and self-interstitials in silicon which are stable to high temperatures. These complexes can then suppress the formation of large vacancy and self-interstitial clusters. However, there is little known about their properties. We use first-principles density-functional theory to the determine the local vibrational modes, electrical levels and stability of a range of nitrogen-interstitial and vacancy complexes. Tentative assignments of the ABC photoluminescence line and the trigonal SL6 EPR center are made to substitutional-nitrogen pair and the substitutional-nitrogen-vacancy complex.
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| 43. |
- Jones, R., et al.
(författare)
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Breakdown of the vacancy model for impurity-vacancy defects in diamond
- 1997
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Ingår i: Defects in semiconductors. - : Trans Tech Publications Inc.. ; , s. 775-780
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Konferensbidrag (refereegranskat)abstract
- The vacancy model for impurity vacancy defects in semiconductors assumes that the ground and low energy excited states are derivable from the four sp3-hybrid orbitals on the atoms bordering the vacancy. There are many cases where this model works but we describe here a counter-example concerning the lowest excited state of the [V-N3] defect in diamond. It is shown that a shallow electron trap, localised outside the vacancy, is involved in the first excited state and responsible for the N2 and N4 optical bands associated with this defect.
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| 44. |
- Jones, R., et al.
(författare)
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Intrinsic defects and the D1 to D4 optical bands detected in plastically deformed Si
- 2000
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Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 222:1, s. 133-140
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Tidskriftsartikel (refereegranskat)abstract
- The properties of multi-vacancy and multi-interstitial defects that possess luminescent bands around 1 eV are reviewed. Prominent among these are the hexavacancy and tri- and tetra-self-interstitial defects. It is suggested that the formation of these defects on dislocation cores could lead to the D1 to D4 photoluminescent bands linked to dislocations in Si and SiGe.
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| 45. |
- Jones, R., et al.
(författare)
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N2 and N4 optical transitions in diamond: A breakdown of the vacancy model
- 1997
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 56:4, s. 1654-1656
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Tidskriftsartikel (refereegranskat)abstract
- The vacancy model for impurity vacancy defects in semiconductors assumes that the ground and low-energy excited states are derivable from the four sp3 hybrid orbitals on atoms bordering the vacancy. There are many cases where this model works but we describe here a counterexample concerning the lowest excited state of the [V-N3] defect in diamond. It is shown that a shallow electron trap, localized outside the vacancy, is involved in the first excited state and responsible for the N2 and N4 optical bands associated with the defect.
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| 46. |
- Jones, R., et al.
(författare)
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Self-interstitial clusters in silicon
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - 0168-583X .- 1872-9584. ; 186:1, s. 10-18
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Tidskriftsartikel (refereegranskat)abstract
- Although there have been many calculations of the structures of the self-interstitial in Si and small aggregates of interstititals, In, there has been little attempt to relate the defects with experimental data. Here we discuss the assignments of the self-interstitial to the AA12 electron paramagnetic resonance (EPR) centre, and the tri-interstitial and tetra-interstitial to the W-optical centre and the B3 EPR centre, respectively. Difficulties in the assignment of I2 to the P6 EPR centre are also noted.
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| 47. |
- Jones, R., et al.
(författare)
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Structure and electronic properties of nitrogen defects in silicon
- 2004
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Ingår i: Gettering and Defect Engineering in Semiconductor Technology GADEST 2003. - : Trans Tech Publications Inc.. ; , s. 93-98
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Konferensbidrag (refereegranskat)abstract
- Nitrogen-vacancy defects in Si are of interest due to their ability to suppress the formation of large vacancy cluster during growth but there are problems in their characterisation. We use local density functional theory to determine the local vibrational modes, electrical levels and stability of a number of nitrogen defects. A prominent nitrogen local vibrational mode at 663 cm-1 is attributed to a nitrogen-vacancy centre and tentative assignments of the ABC photoluminescence line and the trigonal SL6 BPR centre are made.
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| 48. |
- Leigh, R. S., et al.
(författare)
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Vibrational modes of sulfur defects in GaP
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:3
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Tidskriftsartikel (refereegranskat)abstract
- First principles calculations carried out on GaP containing sulfur donors 32SP (95%) and34SP (5%) show that both the neutral and ionized donors are located on substitutional sites and have weak S-Ga bonds. For the sulfur impurity in its positive charge state the calculations give gap modes for 32S and34S at frequencies close to those found experimentally. Modes within the gap are also predicted for neutral sulfur at frequencies within a few cm-1 of their charged-state counterparts. However, the SP0 donor has a very low apparent charge (i.e. oscillator strength), its calculated integrated absorption cross section being only ∼3% of that for the SP+ defect. These results support an earlier explanation of the failure to detect gap modes from SP0 in infrared measurements. Calculated and observed apparent charges for the SP+ donor are compared, and the importance of taking due account of the different geometries that apply to the theoretical calculations and infrared experiments is emphasized.
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| 49. |
- Markevich, A., et al.
(författare)
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First-principles study of hydrogen and fluorine intercalation into graphene-SiC(0001) interface
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:4
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Tidskriftsartikel (refereegranskat)abstract
- The properties of epitaxial graphene on SiC substrates can be modified by intercalation of different atomic species. In this work, mechanisms of hydrogen intercalation into the graphene-SiC(0001) interface, and properties of hydrogen and fluorine intercalated structures have been studied with the use of density functional theory. Our calculations show that the intercalation of hydrogen and fluorine into the interface is energetically favorable. Energy barriers for diffusion of atomic and molecular hydrogen through the interface graphene layer with no defects and graphene layers containing Stone-Wales defect or two- and four-vacancy clusters have been calculated. It is argued that diffusion of hydrogen towards the SiC surface occurs through the hollow defects in the interface graphene layer. It is further shown that hydrogen easily migrates between the graphene layer and the SiC substrate and passivates the surface Si bonds, thus causing the graphene layer decoupling. According to the band structure calculations the graphene layer decoupled from the SiC(0001) surface by hydrogen intercalation is undoped, while that obtained by the fluorine intercalation is p-type doped.
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| 50. |
- Pinto, H., et al.
(författare)
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First-principles studies of the effect of (001) surface terminations on the electronic properties of the negatively charged nitrogen-vacancy defect in diamond
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:4
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Tidskriftsartikel (refereegranskat)abstract
- Density functional calculations have been carried out on (001)-orientated slabs of diamond with different surface terminations. A negatively charged nitrogen-vacancy defect (NV-) is placed in the middle of the slab approximately 1 nm from each surface and the effect of the surface on the internal optical transition in NV- investigated. The calculations show that the chemical nature of the surface is important. We find that although the clean surface does not lead to charge transfer between the defect and the surface, there is a splitting of the empty excited state, the final state in optical absorption, arising from a strong hybridization of the surface and defect bands. This leads to a broadening of the 1.945-eV transition of the NV- defect. OH- and F-terminated surfaces have no surface states in the band gap and again charge transfer between the defect and surface does not occur. The splitting of the e levels responsible for the optical transitions for OH or F termination is similar to that found in periodic boundary condition simulations for bulk diamond where the defects are separated by 1 nm, and thus the calculations show that hydroxylated or fluorinated surfaces give favorable optical properties.
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