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  • 201.
    Goss, J.P.
    et al.
    University of Exeter.
    Coomer, B.J.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Fall, C.J.
    University of Exeter.
    Latham, Chris
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Small aggregates of interstitials and models for platelets in diamond2000Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, nr 49, s. 10257-10261Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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

  • 202.
    Larsen, A Nylandsted
    et al.
    University of Aarhus.
    Goubet, J. J.
    University of Aarhus.
    Mejlholm, P
    University of Aarhus.
    Christensen, J Sherman
    University of Aarhus.
    Fanciulli, M
    University of Aarhus.
    Gunnlaugsson, H P
    University of Aarhus.
    Weyer, G
    University of Aarhus.
    Petersen, J Wulff
    Technical University of Denmark.
    Resende, A
    University of Exeter.
    Kaukoen, K
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Svensson, B G
    Royal Institute of Technology.
    Lindström, J L
    University of Lund.
    Dannefaer, S
    University of Winnipeg.
    Tin-vacancy acceptor levels in electron-irradiated n-type silicon2000Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 62, nr 7, s. 4535-4544Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Si crystals (n-type, fz) with doping levels between 1.5×1014 and 2×1016 cm-3 containing in addition ∼1018 Sn/cm3 were irradiated with 2-MeV electrons to different doses and subsequently studied by deep level transient spectroscopy, Mössbauer spectroscopy, and positron annihilation. Two tin-vacancy (Sn-V) levels at Ec-0.214 eV and Ec-0.501 eV have been identified (Ec denotes the conduction band edge). Based on investigations of the temperature dependence of the electron-capture cross sections, the electric-field dependence of the electron emissivity, the anneal temperature, and the defect-introduction rate, it is concluded that these levels are the double and single acceptor levels, respectively, of the Sn-V pair. These conclusions are in agreement with electronic structure calculations carried out using a local spin-density functional theory, incorporating pseudopotentials to eliminate the core electrons, and applied to large H-terminated clusters. Thus, the Sn-V pair in Si has five different charge states corresponding to four levels in the band gap.

  • 203.
    Hoffmann, L
    et al.
    Aarhus University.
    Lavrov, E V
    Aarhus University.
    Nielsen, B Bech
    Aarhus University.
    Hourahine, B
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Weakly bound carbon-hydrogen complex in silicon2000Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 61, nr 24, s. 16659-16666Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local vibrational modes of a weakly bound carbon-hydrogen complex in silicon have been identified with infrared-absorption spectroscopy. After implantation of protons at ∼20 K and subsequent annealing at 180 K, two carbon modes at 596 and 661 cm-1, and one hydrogen mode at 1885 cm-1 are observed. The three modes originate from the same complex, which is identified as bond-centered hydrogen in the vicinity of a nearby substitutional carbon atom. Ab initio theory has been applied to calculate the structure and local modes of carbon-hydrogen complexes with hydrogen located at the first, second, and third nearest bond-center site to substitutional carbon. The results support our assignment.

  • 204.
    Resende, A
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Calculations of electrical levels of deep centers: application to Au-H and Ag-H defects in silicon1999Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 82, nr 10, s. 2111-2114Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles local-density formalism cluster theory is used to determine the structure of Au- and Ag-hydrogen complexes in Si. The theory, with an empirical correction, is then applied to extract their donor and acceptor levels and these are compared with capacitance transient spectroscopic measurements. Assignments of these levels to specific H defects are then made. Models for the defects responsible for the neutralization of the electrical activity of the Au and Ag centers are proposed.

  • 205.
    Jones, R
    et al.
    University of Exeter.
    Elsner, J
    University of Exeter.
    Haugk, M
    Gutierrez, R
    Frauenheim, Th
    Heggie, M I
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P R
    Interaction of oxygen with threading dislocations in GaN1999Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 171, nr 1, s. 167-173Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A review is given of the results of first principles calculations used to investigate the structures and electronic properties of screw and edge dislocations in GaN. The atoms at the core of the full core screw dislocation possess heavily strained bonds leading to deep gap states. Removing the first shell of Ga and N atoms gives a screw dislocation with a small open core consisting of {101-0} type surfaces. Therefore open-core screw dislocations induce only shallow gap states. In the same way we found the core of the threading edge dislocation to be reconstructed without any deep states. The interaction of oxygen with the cores of open-core screw and edge dislocations is considered and it is found that the impurity has a strong tendency to be bound by Ga vacancies leading to three types of defect trapped in the strain field. We suggest that the most stable defect leads to a poisoning of growth centres on the walls of nanopipes.

  • 206.
    Coomer, B.J.
    et al.
    School of Physics, University of Exeter.
    Goss, J.P.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Interstitial aggregates and a new model for the I1/W optical centre in silicon1999Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 273-274, s. 505-508Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 207.
    Markevich, V.P.
    et al.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Murin, L.I.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Suezawa, M.
    Institute for Materials Research, Tohoku University.
    Lindström, J.C.
    Department of Physics, University of Lund.
    Coutinho, J.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Local vibrational mode bands of V-O-H complexes in silicon1999Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 273-274, s. 300-304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    H2 molecules, which are introduced into moderately doped silicon crystals by high-temperature in-diffusion from H2 gas ambient followed by fast cooling to room temperature, are found to interact effectively with the defects induced by irradiation of the crystals with fast electrons. In Czochralski-grown silicon crystals, the interaction of the mobile H2 molecules with vacancy-oxygen defects (A centers) leads to the creation of V-O-H2 complexes. This complex gives rise to infrared (IR) absorption lines at 943.5, 2126.4, and 2151.5 cm-1. Ab initio calculations showed that the most stable configuration of V-O-H2 consists of one oxygen and two hydrogen atoms sharing a vacancy site. It is suggested that the interaction of the V-O-H2 complexes with interstitial oxygen atoms results in the formation of V-O2-H2 complexes, which are responsible for the IR absorption line at 891.5 cm-1.

  • 208.
    Hourahine, B.
    et al.
    Department of Physics, University of Exeter.
    Jones, r.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Molecular hydrogen traps within silicon1999Ingår i: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 58, nr 1-2, s. 24-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the results of first principle calculations on the behaviour of molecular hydrogen within crystalline silicon, both as an isolated species, and within defects in the material. These results are compared with recent experimental infra-red and Raman data obtained for silicon treated by either hydrogen plasma or soaked in hydrogen gas. The effect of Fermi-level position on the diffusion barrier of molecular hydrogen within silicon is also discussed

  • 209.
    Hourahine, B.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Safonov, A.N.
    Department of Physics, University of Durham.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Estreicher, S.K.
    Department of Physics, Texas Tech University, Lubbock.
    Optically active hydrogen dimers in silicon1999Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 273-274, s. 176-179Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles calculations are used to explore the structure and properties of several defects which are prominent luminescent centers in Si. The trigonal defects B41 and B711, which are known to contain two hydrogen atoms in equivalent and inequivalent sites, respectively, are attributed to a hexavacancy containing two H atoms in different configurations. It is suggested that the J luminescence centers arises from a stable hexavacancy without hydrogen atoms

  • 210.
    Hourahine, B
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Self-interstitial-hydrogen complexes in silicon1999Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 59, nr 24, s. 15729-15732Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The vibrational properties of interstitial silane (SiH4)i and silyl (SiH3)i molecules in crystalline silicon are calculated using a first-principle, cluster-based, spin-polarized local-density method. The Si-H stretch modes are found to be redshifted by ∼300 cm-1 from those of the isolated molecule, which lie around 2200 cm-1. These results refute recent suggestions that modes observed around 2200 cm-1, and previously assigned to hydrogenated vacancy defects, are due to these interstitial molecules.

  • 211.
    Hoffmann, L
    et al.
    Aarhus University.
    Nielsen, B Bech
    Aarhus University.
    Larsen, A Nylandsted
    Aarhus University.
    Leary, P
    University of Exeter.
    Jones, R
    University of Exeter.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Substitutional carbon in Si1-xGex1999Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 60, nr 19, s. 13573-13581Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local vibrational modes of carbon impurities in relaxed Si1-xGex have been studied with infrared absorption spectroscopy in the composition range 0.05<~x<~0.50. Carbon modes with frequencies in the range 512-600 cm-1 are observed in 13C+-implanted Si1-xGex after annealing at 550 °C. Measurements on samples coimplanted with 12C+ and 13C+ show that these modes originate from defects containing a single carbon atom and from the variation of the mode frequencies with composition x, the modes are assigned to substitutional carbon in Si1-xGex. Based on the frequencies obtained from a simple vibrational model, the observed modes are assigned to specific combinations of the four Si and Ge neighbors to the carbon. The intensities of the modes indicate that the combination of the four neighbors deviates from a random distribution. Ab initio local-density-functional cluster theory has been applied to calculate the structure and the local mode frequencies of substitutional carbon with n Ge and 4-n Si neighbors in a Si and a Ge cluster. The calculated frequencies are ∼9% higher than those observed, but the ordering and the splitting of the mode frequencies agree with our assignments.

  • 212.
    Coomer, B.J.
    et al.
    School of Physics, University of Exeter.
    Resende, A.
    School of Physics, University of Exeter.
    Goss, J.P.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    The divacancy in silicon and diamond1999Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 273-274, s. 520-523Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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

  • 213.
    Jones, R.
    et al.
    Department of Physics, University of Exeter.
    Resende, A.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    The electronic properties of transition metal hydrogen complexes in silicon1999Ingår i: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 58, nr 1-2, s. 113-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electrical levels of various combinations of transition metal-Hn defects in Si are calculated using spin-polarised local density functional cluster theory with an empirical correction. The shifts of these levels with H can be understood through a displacement and splitting of the gap t2 manifold of states due to the impurity. Passive defects are identified

  • 214.
    Gutiérrez, R.
    et al.
    Technische Universität, Theoretische Physik III, D-09107 Chemnitz.
    Haugk, M.
    Technische Universität, Theoretische Physik III, D-09107 Chemnitz.
    Frauenheim, Th.
    Technische Universität, Theoretische Physik III, D-09107 Chemnitz.
    Elsner, J.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Heggie, M.I.
    CPES, University of Sussex, Falmer, Brighton.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    The formation of nanopipes caused by donor impurities in GaN1999Ingår i: Philosophical Magazine Letters, ISSN 0950-0839, E-ISSN 1362-3036, Vol. 79, nr 2-3, s. 147-152Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local density-functional methods are used to examine the behaviour of O and O-related defect complexes at {1010}-type surfaces in GaN. We find that O has a tendency to segregate to the (1010) surface and we identify the gallium vacancy surrounded by three oxygen impurities (VGa-(ON)3) to be a particularly stable and electrically inert complex. We suggest that these complexes impede growth at the walls of the nanopipes preventing them from growing in. Also, other donor-related defect complexes, in particular gallium vacancies surrounded by three silicon atoms as second nearest neighbours, are expected to have the same effect.

  • 215.
    Resende, A.
    et al.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    The structural properties of transition metal hydrogen complexes in silicon1999Ingår i: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 58, nr 1-2, s. 146-148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A first-principles spin-polarised local density functional cluster method is used to explore the structural and vibrational properties of several substitutional transition-metal impurities complexed with hydrogen

  • 216.
    Coomer, B.J.
    et al.
    Department of Physics, University of Exeter.
    Leary, P.
    Department of Physics, University of Exeter.
    Budde, M.
    Institute of Physics and Astronomy, University of Aarhus.
    Nielsen, B. Bech
    Institute of Physics and Astronomy, University of Aarhus.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Vacancy-hydrogen complexes in germanium1999Ingår i: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 58, nr 1-2, s. 36-38Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local-density-functional pseudopotential theory is used to investigate the structural, electronic and vibrational properties of vacancy-hydrogen complexes in germanium. The results are compared with recent infrared absorption data from proton and deuteron implanted Ge. The acceptor and donor levels of the VHn defects are derived semi-empirically from the relaxed structures

  • 217.
    Elsner, J
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Heggie, M I
    University of Sussex.
    Sitch, P K
    Technische Universität, Chemnitz.
    Haugk, M
    Technische Universität, Chemnitz.
    Frauenheim, Th
    Technische Universität, Chemnitz.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Deep acceptors trapped at threading-edge dislocations in GaN1998Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 58, nr 19, s. 12571-12574Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local-density-functional methods are used to examine the behavior of the oxygen defect, gallium vacancy, and related defect complexes trapped at threading-edge dislocations in GaN. These defects are found to be particularly stable at the core of the dislocation where oxygen sits twofold coordinated in a bridge position. VGa-ON is found to be a deep double acceptor, VGa-(ON)2 is a deep single acceptor, and VGa-(ON)3 at the dislocation core is electrically inactive. We suggest that the first two defects are responsible for a deep acceptor level associated with the midgap yellow luminescence band.

  • 218.
    Latham, Chris D.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jones, R.
    School of Physics, University of Exeter.
    Wagner, J.
    Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastrasse 72, D-79108 Freiburg.
    Davidson, B.R.
    Interdisciplinary Research Centre for Semiconductor Materials, The Blackett Laboratory, Imperial College of Science, Technology and Medicine, London.
    Newman, R.C.
    Interdisciplinary Research Centre for Semiconductor Materials, The Blackett Laboratory, Imperial College of Science, Technology and Medicine, London.
    Button, C.C.
    Department of Electronic and Electrical Engineering, University of Surrey, Guildford.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Di-carbon complexes in AlAs and GaAs1998Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 210, nr 2, s. 869-872Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Heat treatment of heavily carbon doped AlAs and GaAs results in a loss of CAS shallow acceptors. In Raman scattering experiments on annealed CBE grown GaAs with 12C and 13C isotopes, and MOVPE grown AlAs it is found that the loss of carriers is accompanied by the appearance of two high frequency lines. These lie near to the stretch mode of an isolated C2 molecule (1855 cm-1). This is consistent with the formation of two types of di-carbon defects in these materials where the C atoms are bonded together and one or both of which act as a donor. Using a local density functional method to investigate the structure and dynamics of several di-carbon defects, we find that the dimer at an As site is bistable and aligned approximately in a [100] direction in the neutral charge state, and in a [110] direction when positively ionised. The calculated frequencies lie within 10% of the measured values in both materials. Other defects are investigated too with a view of determining the structures giving rise to the modes

  • 219.
    Elsner, J.
    et al.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Haugk, M.
    Technische Universität, Theoretische Physik III, D-09107 Chemnitz.
    Gutierrez, R.
    Technische Universität, Theoretische Physik III, D-09107 Chemnitz.
    Frauenheim, Th.
    Theoretische Physik III, TU Chemnitz.
    Heggie, M.I.
    CPES, University of Sussex, Falmer, Brighton.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Effect of oxygen on the growth of (101‾0) GaN surfaces: The formation of nanopipes1998Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 73, nr 24, s. 3530-3532Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local density-functional methods are used to examine the behavior of O and O-related defect complexes on the walls of nanopipes in GaN. We find that O has a tendency to segregate to the (10 1̄ 0) surface and identify the gallium vacancy surrounded by three oxygen impurities [VGa-(ON)3] to be a particularly stable and electrically inert complex. We suggest that during Stranski-Krastanow growth, when interisland spaces shrink, these defects reach a critical concentration beyond which further growth is prevented and nanopipes are formed

  • 220.
    Lehto, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Effects of dislocation interactions: application to the period-doubled core of the 90° partial in silicon1998Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 80, nr 25, s. 5568-71Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The elastic strain field of a dislocation is highly affected by nearby dislocations. The effects of dislocation-dislocation interactions on elastic energy and core structure are analyzed using a new and self-consistent method to apply periodic boundary conditions on unit cells containing dislocations. Local density functional theory on hydrogen terminated clusters is used to gauge the effects of long-range elastic fields on the core structure of the 90° partial in silicon. It is shown that the single and double period structures of this core are very close in energy, and that the structure adopted probably depends on the environment in which the dislocation is located

  • 221.
    Öberg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Ewels, C P
    University of Exeter.
    Jones, R
    University of Exeter.
    Hallberg, T
    Linköping University.
    Lindström, J L
    Linköping University.
    Murin, L I
    Institute of Solid State and Semiconductor Physics, Minsk.
    Briddon, P R
    University of Newcastle Upon Tyne.
    First stage of oxygen aggregation in silicon: the oxygen dimer1998Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 81, nr 14, s. 2930-2933Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure and dynamic properties of the interstitial oxygen dimer in silicon are found using a combination of infrared spectroscopy and ab initio modeling. We find that the stable dimer consists of a pair of inequivalent weakly coupled interstitial oxygen atoms separated by a Si-Si bond. Two high frequency modes are decoupled in one 16O-18O combination but are strongly mixed in the other combination. A third lower lying mode involves the compression of the Si-Si bond joining the oxygen atoms and gives distinct modes in the mixed 16O-18O case.

  • 222.
    Hourahine, B
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Newman, R C
    Imperial College London.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Roduner, E
    Institut für Physikalische Chemie, Stuttgart.
    Hydrogen molecules in silicon located at interstitial sites and trapped in voids1998Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 57, nr 20, s. 12666-12669Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The vibrational modes of H2 molecules in Si are found using a first-principles method and compared with recent experimental investigations. The isolated molecule is found to lie at a Td interstitial site, oriented along [011] and is infrared active. The rotational barrier is at least 0.17 eV. The molecular frequency is a sensitive function of cage size and increases to lie close to the gas value for cages about 50% larger than the Td site. It is suggested that Raman-active modes around 4158 cm-1 are due to molecules within voids.

  • 223.
    Budde, M
    et al.
    University of Aarhus.
    Nielsen, B Bech
    University of Aarhus.
    Leary, P
    University of Exeter.
    Goss, J
    University of Exeter.
    Jones, R
    University of Exeter.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Breuer, S J
    University of Edinburgh.
    Identification of the hydrogen-saturated self-interstitials in silicon and germanium1998Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 57, nr 18, s. 4397-4412Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 224.
    Leary, P.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Interaction of hydrogen with substitutional and interstitial carbon defects in silicon1998Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 57, nr 7, s. 3887-3889Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An ab initio cluster method is used to investigate substitutional, Cs, and interstitial, Ci, carbon defects in silicon complexed with hydrogen. We find that the binding energy of neutral H with Cs is 1.01 eV, and that the defect is bistable. In the positive and neutral charge states H lies near the center of a C-Si bond, and is antibonded to C in the negative charge state. A second H atom can be trapped in a H2* defect. H forms stronger bonds with interstitial Ci. In the Ci-H defect, the binding energy of H is 2.8 eV, and two low-energy structures have almost degenerate energies. These consist of a bond-centered Si-(Ci-H)-Si defect and a 〈100〉-oriented Ci-Si split interstitial with H bonded to Ci. The calculated barrier for conversion between the two stable structures is very low, ∼0.3 eV, implying that the defect migrates rapidly, and readily reacts with other defects or impurities present. Two possible reactions are considered: the first is with another H and the second with Cs. The defect is completely passivated in the former while the stable form of the latter consists of a 〈100〉 C-C dicarbon interstitial, where one radical is passivated by H. The calculated symmetry and the local vibrational modes are in excellent agreement with those experimentally observed for the T photoluminescent center. Finally, a further reaction involving the T center and a second H atom is considered, and is found to lead to the elimination of electrical activity.

  • 225.
    Hourahine, B.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Molecular hydrogen traps within silicon1998Ingår i: E-MRS Meeting, European Materials Research Society , 1998Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present the results of rst principle calculations on the behaviour of molecular hydrogen within crystalline silicon, both as an isolated species, and within defects in the material. These results are compared with recent experimental infra-red and Raman data obtained for silicon treated by either hydrogen plasma or soaked in hydrogen gas. The effect of Fermi level position on the diffusion barrier of molecular hydrogen within silicon is also discussed.

  • 226.
    Dixon, P.
    et al.
    School of Physics, University of Exeter.
    Richardson, D.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Latham, Chris D.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Torres, V.J.B.
    Departamento de Fisica, Universidade de Aveiro.
    Brikddon, P.R.
    Department of Physics, University of Newcastle.
    Nitrogen-Hydrogen Defects in GaP1998Ingår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 210, nr 2, s. 321-326Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Models of the nitrogen-hydrogen defect in GaP, which contain one and two H atoms, are investigated using ab initio density functional cluster theory. We find that a single H atom binding to N possesses two infrared absorption frequencies close to those attributed to an NH2 defect. The modes shift with its charge state consistent with the photo-sensitivity found for the defect. A third mode observed for this centre is assumed to be an overtone of the bend mode. The isotope shifts of the calculated modes are in excellent agreement with experiment in contrast with the model which contains two H atoms

  • 227.
    Jones, R.
    et al.
    University of Exeter.
    Resende, A.
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    The electronic properties of transition metal hydrogen complexes in silicon1998Ingår i: E-MRS Meeting, European Materials Research Society , 1998Konferensbidrag (Refereegranskat)
    Abstract [en]

    The electrical levels of various combinations of transition metal-H defects in Si are calculated using spin-polarised local density functional cluster theory with an empirical correction. The shifts of these levels with H can be understood through a displacement and splitting of the gap manifold of states due to the impurity. Passive defects are identified.

  • 228.
    Resende, A.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    The structural properties of transition metal hydrogen complexes in silicon1998Ingår i: E-MRS Meeting, European Materials Research Society , 1998Konferensbidrag (Refereegranskat)
    Abstract [en]

    A first-principles spin-polarised local density functional cluster method is used to explore the structural and vibrational properties of several substitutional transition-metal impurities complexed with hydrogen.

  • 229.
    Coomer, B.J.
    et al.
    University of Exeter.
    Leary, P.
    University of Exeter.
    Budde, M.
    Aarhus University.
    Nielsen, B. Bech
    Aarhus University.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Vacancy-hydrogen complexes in germanium1998Ingår i: E-MRS Meeting, European Materials Research Society , 1998Konferensbidrag (Refereegranskat)
    Abstract [en]

    Local-density-functional pseudopotential theory is used to investigate the structural, electronic and vibrational properties of vacancy-hydrogen complexes in germanium. The results are compared with recent infrared absorption data from proton and deuteron implanted Ge. The acceptor and donor levels of the VH defects are derived semi-empirically from the relaxed structures

  • 230.
    Goss, J.P.
    et al.
    School of Physical Sciences, Dublin City University.
    Jones, R.
    Department of Physics, University of Exeter.
    Breuer, S.J.
    Edinburgh Parallel Computing Centre, University of Edinburgh.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    A first principles study of interstitial Si in diamond1997Ingår i: Defects in Semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 781-786Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 231.
    Sitch, P.K.
    et al.
    Institut für Physik, Technische Universität, Chemnitz.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Heggie, M.I.
    School of Chemistry and Molecular Sciences, University of Sussex.
    An ab initio study of the 90° partial dislocation core in diamond1997Ingår i: Journal de Physique III, ISSN 1155-4320, E-ISSN 1286-4897, Vol. 7, nr 7, s. 1381-1387Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic and structural properties of the 90° glide partial dislocation in diamond are investigated using an ab initio local density functional cluster method. The core C-C bond is found to be reconstructed with a bond length 5% longer than that in bulk diamond. The formation and migration energy of the kink on the dislocation are calculated to be 0.32 and 2.97 eV respectively. Further, the shift of the gap levels during kink motion suggests that p-type doping will lead to an increase in the mobility of the partial.

  • 232.
    Hourahine, B.
    et al.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Anomalous shift of the 1075 cm-1 oxygen-hydrogen defect in silicon1997Ingår i: Defects in semiconductors: : proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 277-282Konferensbidrag (Refereegranskat)
    Abstract [en]

    First principles calculations are carried out on i) hydrogen and ii) water molecules trapped near an interstitial oxygen atom in Si. We find that it is possible for these molecules to cause an upward shift in the antisymmetric stretch mode of Oi when H is replaced by D, which could explain the anomalous shift in the 1075 cm-1 O-H related local vibrational mode. Both these molecules lead to modes in the 3500-4000 cm-1 region but those of the H2 lie close to those recently detected using Fourier transform infra-red spectroscopy.

  • 233.
    Jones, R.
    et al.
    Department of Physics, University of Exeter.
    Goss, J.P.
    Department of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Breakdown of the vacancy model for impurity-vacancy defects in diamond1997Ingår i: Defects in semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 775-780Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 234.
    Goss, J.P.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    (CAs)2-hydrogen defects in GaAs: a first-principles study1997Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 55, nr 23, s. 15576-15580Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 235.
    Wagner, J
    et al.
    Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastrasse 72, D-79108 Freiburg.
    Newman, R C
    Imperial College of Science.
    Davidson, B R
    Imperial College of Science.
    Westwater, S P
    University of Liverpool.
    Bullough, T J
    University of Liverpool.
    Joyce, T B
    University of Liverpool.
    Latham, Chris
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Di-Carbon defects in annealed highly carbon doped GaAs1997Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 78, nr 1, s. 74-77Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Formation of bonded dicarbon C-C centers is deduced from the observation of Raman lines at 1742, 1708, and 1674 cm -1 in GaAs codoped with 12C and 13C after annealing at 850 °C with concomitant loss of vibrational scattering from CAs. The frequencies agree with results of ab initio theory for a C-C split interstitial (deep donor) formed by the trapping of a mobile interstitial C (displaced CAs) atom by an undisplaced CAs acceptor. Other mechanisms of carrier loss are inferred since a weaker Raman triplet is detected at 1859, 1824, and 1788 cm -1 from a different C-C complex.

  • 236.
    Leary, P
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Torres, V J B
    Universidade de Aveiro.
    Dynamic properties of interstitial carbon and carbon-carbon pair defects in silicon1997Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 55, nr 4, s. 2188-2194Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Interstitial carbon, Ci, defects in Si exhibit a number of unexplained features. The Ci defect in the neutral charge state gives rise to two almost degenerate vibrational modes at 920 and 931 cm-1 whose 2:1 absorption intensity ratio naturally suggests a trigonal defect in conflict with uniaxial stress measurements. The dicarbon, Cs-Ci, defect is bistable, and the energy difference between its A and B forms is surprisingly small even though the bonding is very different. In the B form appropriate to the neutral charge state, a silicon interstitial is believed to be located near a bond-centered site between two Cs atoms. This must give rise to vibrational modes which involve the motion of both C atoms in apparent conflict with the results of photoluminescence experiments. We use an ab initio local density functional cluster method, AIMPRO, to calculate the structure and vibrational modes of these defects and find that the ratio of the absorption intensities of the local modes of Ci is in reasonable agreement with experiment even though the structure of the defect is not trigonal. We also show that modes in the vicinity of those detected by photoluminescence for the B form of the dicarbon center involve independent movements of the two C atoms. Finally, the trends in the relative energies of the A and B forms in three charge states are investigated.

  • 237. Hoffmann, L
    et al.
    Bach, J C
    Nielsen, B Bech
    Leary, P
    Jones, R
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Erratum: Substitutional carbon in germanium [Phys. Rev. B 55, 11 167 (1997)]1997Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 56, nr 13, s. 8434-8434Artikel i tidskrift (Övrigt vetenskapligt)
  • 238.
    Lehto, Niklas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Interaction of vacancies with partial dislocations in silicon1997Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 56, nr 20, s. R12706-R12709Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interaction of vacancies with 30° and 90° partial dislocations in silicon is examined. In particular, the structures and binding energies are calculated using hydrogen-terminated clusters and local density-functional theory. Moreover the electronic structure is determined using supercells containing dislocation dipoles. Vacancies are found to have binding energies of approximately 2.0 eV and 0.9 eV to 90° and 30° partials, respectively. The elastic strain field of the partials makes the fourfold vacancy reconstruct, which essentially clears the fundamental gap

  • 239.
    Leary, P.
    et al.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Jones, R.
    Department of Physics, University of Exeter.
    Interstitial carbon-hydrogen defects in silicon1997Ingår i: Defects in semiconductors: : proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 265-270Konferensbidrag (Refereegranskat)
    Abstract [en]

    Interstitial carbon, in contrast with substitutional carbon, forms defects with hydrogen which are both electrically active and stable to high temperatures. Ab initio cluster calculations show that the most primitive defect, CiH, diffuses very rapidly and is expected to complex with many other impurities notably C, H and O. We describe here the structure and properties of Ci,nHm defects where n and m are less than 3. The most stable defects of the type CiCsHm have very different structures when m = 0 and when m > 0. In the former case, the C-C bond is metastable and only C-Si-C bonds are formed. However in the second case, the presence of a H atom stabilises the C-C bond. These results are supported by experiment. We show that the vibrational modes of the Cs-CiH defect are close to those observed for the T-photoluminescent centre and this defect is passivated when complexed with a further H atom. This defect then provides the first example of a fully characterised carbon centre containing a C-C bond.

  • 240.
    Nielsen, B. Bach
    et al.
    Institute of Physics and Astronomy, University of Aarhus.
    Tanderup, K.
    Institute of Physics and Astronomy, University of Aarhus.
    Budde, M.
    Institute of Physics and Astronomy, University of Aarhus.
    Bonde-Nielsen, K.
    Institute of Physics and Astronomy, University of Aarhus.
    Lindström, J.L.
    Department of Physics, Linköping University.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hourahine, B.
    Department of Physics, University of Newcastle.
    Briddon, P.
    Department of Physics, University of Newcastle.
    Local vibrational modes of weakly bound O-H complexes in SI1997Ingår i: Defects in semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 391-398Konferensbidrag (Refereegranskat)
    Abstract [en]

    Local vibrational modes of two oxygen-hydrogen complexes have been identified with infrared absorption spectroscopy. Samples of intrinsic silicon and samples doped with 16O or 18O isotopes were implanted with protons and deuterons at ∼20 K. After the implantation, infrared absorbance spectra were measured at 8 K on unannealed samples. An oxygen mode at 1077 cm-1 and a hydrogen mode at 1879 cm-1, which originate from the same defect OHI were observed in the as-implanted samples. Heat-treatment at 200 K produced a new center OHII with modes at 1028 and 1830 cm-1. OHI anneals out at ∼130 K while OHII is stable up to ∼240 K. OHI and OHII are tentatively identified with two complexes of interstitial oxygen and bond-centred hydrogen. Ab initio theory was applied to calculate the structure and local modes of three such complexes. The results qualitatively support our tentative assignments.

  • 241.
    Jones, R.
    et al.
    University of Exeter.
    Goss, J.P.
    University of Exeter.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    N2 and N4 optical transitions in diamond: a breakdown of the vacancy model1997Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 56, nr 4, s. 1654-1656Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 242. Elsner, J.
    et al.
    Jones, R.
    Department of Physics, University of Exeter.
    Sitch, P.K.
    Frauenheim, Th.
    Theoretische Physik III, TU Chemnitz.
    Heggie, M.I.
    CPES, University of Sussex, Falmer, Brighton.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Structural and electrical properties of threading dislocations in GaN1997Ingår i: Defects in semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 1203-1210Konferensbidrag (Refereegranskat)
    Abstract [en]

    The atomic structures and electrical properties for threading screw and threading edge dislocations of wurtzite GaN are calculated within the local-density approximation. Both dislocations are electrically inactive with a band gap free from deep levels. These results are understood to arise from relaxed core structures which are similar to (1010) surfaces. The threading screw dislocations are found to be stable with an open-core whereas the threading edge dislocations possess filled cores.

  • 243.
    Hoffmann, L.
    et al.
    Institute of Physics and Astronomy, University of Aarhus.
    Bach, J.C.
    Institute of Physics and Astronomy, University of Aarhus.
    Hansen, J. Lundsgaard
    Institute of Physics and Astronomy, University of Aarhus.
    Larsen, A. Nylandsted
    Institute of Physics and Astronomy, University of Aarhus.
    Nielsen, B. Bech
    Institute of Physics and Astronomy, University of Aarhus.
    Leary, P.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Substitutional carbon in Ge and Si1-xGex1997Ingår i: Defects in semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 97-102Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the present work, carbon is implanted into monocrystalline Ge and into relaxed epitaxial MBE-grown Si1-xGex. The samples are studied with infrared absorption spectroscopy along with ion-channeling studies on the Ge samples. Finally, ab-initio local density functional cluster theory is applied to calculate the structure and the local vibrational modes of substitutional carbon, Cs, in Ge. After implantation of 12C+ in Ge at room temperature and subsequent annealing at 350°C, a sharp absorption line is observed at 531 cm-1. By isotope substitution, it is concluded that the 531 cm-1 line represents a local vibrational mode of a single carbon atom. From ion-channeling measurements on samples annealed at 450°C, it is found that 31±3 % of the carbon atoms are located at substitutional sites. The population of the substitutional site and the intensity of the 531 cm-1 mode have identical annealing behavior and it is concluded that the 531 cm-1 mode is the three-dimensional T2 stretch mode of Cs in Ge. The calculated frequency and isotope shift for this mode are in good agreement with the observations. In Si0.65Ge0.35, two broad absorption lines are observed at ∼551 and ∼592 cm-1 after implantation of 12C+ and subsequent annealing at 550°C. From measurements on samples implanted with 13C+ and coimplanted with 12C+ and 13C+ we conclude that these lines represent local vibrational modes of defects containing a single carbon atom. In 13C+ implanted Si1-xGex samples that contain 15 to 50 % Ge a number of modes are observed in a frequency range from ∼510 to ∼610 cm-1, i.e., in the range of Cs in Ge and in Si. From the experimental findings it is concluded that substitutional carbon in Si1-xGex binds to both Si and Ge.

  • 244.
    Hoffmann, L
    et al.
    Aarhus University.
    Bach, J C
    Aarhus University.
    Nielsen, B Bech
    Aarhus University.
    Leary, P
    University of Exeter.
    Jones, R
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Substitutional carbon in germanium1997Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 55, nr 17, s. 11167-11173Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon impurities implanted into single-crystalline germanium are studied with infrared absorption spectroscopy and ion channeling. After implantation of 12C+ at room temperature and subsequent annealing at 350 °C, a sharp infrared absorption line is observed at 531 cm-1. When 12C+ is substituted by 13C+, the line shifts down in frequency to 512 cm-1 and co-implantation of 12C+ and 13C+ does not give rise to additional lines. Therefore, the 531-cm-1 line represents a local vibrational mode of a defect containing a single carbon atom. Channeling measurements are carried out around the 〈100〉, 〈110〉, and 〈111〉 axes in 12C+-implanted samples annealed at 450 °C. The analysis of the data shows that 31±3 % of the carbon atoms are located at substitutional sites, while the remaining carbon atoms appear to be located randomly. The population of the substitutional site and the intensity of the 531-cm-1 mode have identical temperature dependencies. It is concluded that the 531-cm-1 mode is the three-dimensional T2 stretch mode of substitutional carbon. The effective charge of the mode is determined to be (3.4±0.5)e.mAb initio local density functional cluster theory is applied to calculate the structure and the local vibrational modes of substitutional carbon in germanium. The calculated frequencies and isotope shifts for the T2 stretch mode are in good agreement with the observations.

  • 245.
    Budde, M.
    et al.
    Institute of Physics and Astronomy, University of Aarhus.
    Nielsen, B. Bach
    Institute of Physics and Astronomy, University of Aarhus.
    Leary, P.
    Department of Physics, University of Exeter.
    Goss, J.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Breuer, ¨S.J.
    Edinburgh Parallel Computing Centre, University of Edinburgh.
    The hydrogen-saturated self-interstitial in silicon and germanium1997Ingår i: Defects in semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 35-40Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 246.
    Torres, V.J.B.
    et al.
    Departamento de Fisica, Universidade de Aveiro.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jones, R.
    Department of Physics, University of Exeter.
    Theoretical studies of hydrogen passivated substitutional magnesium acceptor in wurzite GaN1997Ingår i: MRS Internet journal of nitride semiconductor research, ISSN 1092-5783, E-ISSN 1092-5783, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Infrared measurements on wurzite GaN codoped with Mg and H reveal strong absorption at 3125 cm-1, Theorectical work provides strong evidence for the H being antibonding to N. We have performed an ab-initio study of Mg-H complexes in wurzite GaN, using the Local Density Approximation on a large H-terminated cluster MgHGa25N26H42. We have investigated the physical properties of three neutral configurations along the c direction. In all configurations Mg sits in a gallium substitutional site. H is then located in the Mg-N bond centre (BC), in the antibonding site on nitrogen side (ABN) or in the antibonding position on magnesium side (AB Mg). We found the lowest total energy configuration is hydrogen in the antibonding on the nitrogen site. The stretch mode in this configuration is calculated at 3277 cm-1 which agrees with experiment and previous LDA calculations and we predict an unreported infra red active wag mode at 1311 cm-1. The experimental isotopic shift with D is well reproduced. The BC and ABMg configurations are 0.5 and 3.7eV higher, producing local modes at 3645 and 2144cm-1, respectively. No wag modes appear for the BC and ABMg configurations.

  • 247. Resende, A
    et al.
    Goss, J
    Briddon, P R
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jones, R
    Theory of gold-hydrogen complexes in silicon1997Ingår i: Defects in Semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / ICDS-19 / [ed] Gordon Davies, Uetikon-Zuerich: Trans Tech Publications Inc., 1997, s. 295-300Konferensbidrag (Refereegranskat)
  • 248.
    Torres, V.J.B.
    et al.
    Departamento de Física, Universidade de Aveiro, 3810 Aveiro, Portugal.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jones, R.
    Department of Physics, University of Exeter.
    Theory of nitrogen-hydrogen complexes in GaP1997Ingår i: Defects in semiconductors: proceedings of the 19th International Conference on Defects in Semiconductors, Aveiro, Portugal, July 1997 / [ed] Gordon Davies, Trans Tech Publications Inc., 1997, s. 1063-1068Konferensbidrag (Refereegranskat)
    Abstract [en]

    Nitrogen in GaP is an isoelectronic acceptor. Due to its much higher electronegativity than phosphorus, nitrogen forms bound excitons. This had made possible the fabrication of LEDs from an indirect band gap material. A spectrocopic study of N-H complexes in GaP grown by LEC technology shows that two hydrogens and one nitrogen are involved, existing in three different states; two of them corresponding to different charged states. One of this centres does not show gallium isotope shift, resulting that both hydrogens are bonded to the nitrogen, the nitrogen being five fold coordinated. We investigated this new NH2 configuration using ab-initio calculations on a HNHGa22P21H42 cluster. As this centre has C3v symmetry, nitrogen is positioned in a phosphorus site, one hydrogen is antibonding on nitrogen and the other at bond centre, both along a 〈111〉 direction. We found the hydrogen at bond centre prefers to bond to nitrogen for the double positive charged state, with the nitrogen five folded coordinated. This configuration is metastable for the singly positive charged state. The last two states have very similar configurations, being the plane formed by the three Ga atoms and nitrogen perpendicular to the H-N-H direction, very similar to the NH5+2 molecule. A vibrational analysis of the NHNGa3+2 cluster is in a good agreement with experiment.

  • 249.
    Elsner, J
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Stich, P K
    Technische Universität, Chemnitz.
    Porezag, V D
    Technische Universität, Chemnitz.
    Elstner, M
    Technische Universität, Chemnitz.
    Frauenheim, Th
    Technische Universität, Chemnitz.
    Heggie, M I
    University of Sussex.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Theory of threading edge and screw dislocations in GaN1997Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 79, nr 19, s. 3672-3675Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The atomic structures, electrical properties, and line energies for threading screw and threading edge dislocations of wurtzite GaN are calculated within the local-density approximation. Both dislocations are electrically inactive with a band gap free from deep levels. These results are understood to arise from relaxed core structures which are similar to (101̅ 0) surfaces.

  • 250.
    Breuer, S J
    et al.
    University of Exeter.
    Jones, R
    University of Exeter.
    Briddon, P R
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Interstitial hydrogen and enhanced dissociation of C-H complexes in GaAs1996Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 53, nr 24, s. 16289-16296Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local-density-functional-based ab initio calculations are used to investigate hydrogen and carbon-hydrogen defects in GaAs. The equilibrium structure for both the C-H and C-H- complexes are shown to be similar, with the hydrogen located at a C-Ga bond-centered site. The dissociation of these complexes is investigated and it is found that the energy barrier of 1.84 eV for the process C-H → C- + H+ is substantially lowered to 0.88 eV in the presence of an electron resonantly bound to the defect. This is in good quantitative agreement with recent experiments. Isolated interstitial hydrogen is found to lie at a Ga-As bond-centered site for both H+ and H0 and at an antibonding site relative to a Ga atom for H-. It is also found that the stable form of the hydrogen dimer is a H2 molecule, the dissociation energy of which is 1.64 eV, and that interstitial hydrogen is a negative-U defect. Finally, a mechanism for minority-carrier-induced device degradation is proposed.

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