Ändra sökning
Avgränsa sökresultatet
123456 101 - 150 av 288
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 101. Latham, Chris
    et al.
    Ganchenkova, M.
    Laboratory of Physics, Helsinki University of Technology.
    Nieminen, R.M.
    Laboratory of Physics, Helsinki University of Technology.
    Nicolaysen, S.
    Department of Physics, University of Oslo.
    Alatalo, M.
    Department of Electrical Engineering, Lappeenranta University of Technology.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Electronic structure calculations for substitutional copper and monovacancies in silicon2006Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 2006, nr T126, s. 61-64Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two different computer program packages based on the self-consistent local-spin-density approximation-aimpro and vasp-are employed in this study of substitutional copper CuSi and monovacancies VSi in silicon, including the effects of their charge state. The programs differ in the types of basis sets and pseudopotentials they use, each with their own relative merits, while being similar in overall quality. This approach aims to reduce uncertainty in the results, particularly for small or subtle effects, where the risk is greatest that the conclusions are affected by artifacts specific to a particular implementation. The electronic structures of the two defects are closely related, hence they are expected to behave in a similar manner. For both defects structural distortions resulting in lower point group symmetries than Td (the highest possible) are found. This is in good agreement with the results of previous studies of VSi. Much less is known about symmetry-lowering effects for CuSi; however, the electronic levels of CuSi have been measured accurately, while those for VSi are less accessible. Calculating them is a challenging task for theory. The strategy we adopt, based purely on comparing total energies of supercells in different charge states, with and without model defects, reproduces the three known levels for CuSi reasonably well. Satisfactory results are also obtained for VSi in so far as can be judged for this more complex case.

  • 102.
    Fujita, Naomi
    et al.
    University of Exeter.
    Jones, Robert
    University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, Patrick
    University of Newcastle Upon Tyne.
    First-principle study on the identification of nitrogen-oxygen defect complexes in silicon2006Ingår i: High purity silicon 9: [proceedings of the Ninth High Purity Silicon Symposium held in Cancun, Mexico at the 210th meeting of the Electrochemical Society, Oct. 29 - Nov. 3, 2006], Electrochemical Society, Incorporated , 2006, s. 127-133Konferensbidrag (Refereegranskat)
    Abstract [en]

    Local density functional theory is used to investigate theinteraction of nitrogen with oxygen in Cz-Si. The binding energyof O with N2 and the positions of four local vibrational modesof the N2O center are in good agreement with experiment. TheN2O2 defect is the most common nitrogen-oxygen defect after N2Oand we suggest that the experimentally observed lines at 1018and 810 cm-1 are due to this defect. The concentrations of thesedefects are greater than those of oxygen dimers at temperatures around 650{degree sign}C. Furthermore thesedefects could be nuclei for oxygen precipitates in nitrogendoped Cz-Si.Neither NO nor NO2 play any significant role.

  • 103.
    Pinto, H.M.
    et al.
    Department of Physics, University of Minho, Campus de Gualtar, 4710-553 Braga.
    Coutinho, J.
    Department of Physics, University of Aveiro.
    Torres, V.J.B.
    Department of Physics, University of Aveiro.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Formation energy and migration barrier of a Ge vacancy from ab initio studies2006Ingår i: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 9, nr 4-5, s. 498-502Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here we present local density functional calculations of the formation and migration energies of a vacancy in large Ge supercells and hydrogen-terminated Ge clusters. Migration barriers for neutral (V0), negatively charged (V-) and double negatively charged (V=) vacancies were calculated by using symmetry-constrained atomic relaxations, as well as a nudged elastic band scheme. The formation energy of the neutral vacancy is estimated at 2.6 eV, whereas 0.4, 0.1 and 0.04 eV are obtained for migration barriers of V0, V- and V=, respectively. These figures account well for the formation kinetics of vacancy-impurity complexes in Ge at cryogenic temperatures, and are also in line with measured self-diffusion activation barriers obtained at elevated temperatures

  • 104.
    Hounsome, L.S.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Martineau, P.M.
    DTC, Maidenhead.
    Fisher, D.
    DTC, Maidenhead.
    Shaw, M.J.
    Centre, School of Natural Science, Newcastle upon Tyne.
    Briddon, P.R.
    Centre, School of Natural Science, Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Origin of brown coloration in diamond2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 12, s. 125203-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measurements of the absorption spectra of brown natural type IIa diamond as well as brown nitrogen-doped CVD diamond are reported. These are largely featureless and increase almost monotonically from about 1-5.5 eV. It is argued that the brown coloration is due to an extended defect and not to a point defect. First principles modeling studies demonstrate that the spectra could be attributed to vacancy disks lying on {111} planes. Such disks are unstable above about 200 vacancies and should relax to dislocation loops in natural diamond. Hydrogen is shown to passivate the optical activity of the disks.

  • 105. Savini, G.
    et al.
    Heggie, M.I.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Peierls barriers and core properties of partial dislocations in 4H-SiC2006Ingår i: Silicon carbide and related materials : [ICSCRM 2005]: proceedings of the International Conference on Silicon Carbide and Related Materials, Pittsburgh, Pennsylvania, USA, September 18-23, 2005 / [ed] Robert P. Devaty; David J. Larkin; Stephen E. Saddow, Stafa-Zuerich: Trans Tech Publications Inc., 2006, Vol. 2, s. 359-362Konferensbidrag (Refereegranskat)
    Abstract [en]

    First-principles calculations are used to investigate the partial dislocations in 4H-SiC. We show that the stability of the dislocation cores and the Peierls barriers of the first kind are charge-state dependent. In intrinsic bulk the partials are stable in the neutral asymmetric reconstructions. These reconstructions have no deep states and are characterized by high Peierls barriers. In strongly doped regime the symmetric reconstructions can become more stable. These reconstructions are always electrically active with a half filled band across the band gap. In particular the symmetric reconstructions of the 30° partial have a lower Peierls barriers than the respective asymmetric ones and could be the cause of the 1.8 eV electroluminescence peak observed under carrier injection conditions.

  • 106.
    Carvahlo, A.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Coutinho, J.
    Department of Physics, University of Aveiro.
    Shaw, M.
    School of Natural Science, University of Newcastle upon Tyne.
    Torres, V.J.B.
    Department of Physics, University of Aveiro.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Studies of the VO centre in Ge using first principles cluster calculations2006Ingår i: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 9, nr 4-5, s. 489-493Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The small or near-zero band gap of germanium found by supercell local density functional treatments causes difficulties in the study of the properties of charged defects in Ge. Here, we use large H-terminated Ge clusters together with a non-linear core corrected (NLCC) Ge pseudopotential to explore the structure, vibrational and electrical properties of the vacancy-oxygen complex (VO). The cluster possesses a gap sufficiently wide to contain defect related energy levels, thus allowing us to model the three charge states of the defect. The local vibrational modes (LVM) calculated for the neutral (VO0), negatively charged (VO-) and double negative (VO=) defect are 602, 684 and 694 cm- 1, and can be favourably compared with experimental values of 621, 669 and 716 cm- 1, respectively [Markevich VP, et al. Physica B 2003; 340-2, 844-8]. Using substitutional gold (Aus) as a marker defect, electric levels of VO are found at E (-/ 0) = Ev + 0.30 eV and E (= /-) = Ec - 0.29 eV, in excellent agreement with the respective experimental enthalpies for hole and electron emission Δ Hh (-/ 0) ≃ 0.32 eV and Δ He (= /-) = 0.26 eV, respectively. Finally, the migration, dissociation and reorientation energies of the defect are also reported.

  • 107.
    Janke, C.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Coutinho, J.
    Department of Physics, University of Aveiro.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Supercell and cluster density functional calculations of the thermal stability of the divacancy in germanium2006Ingår i: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 9, nr 4-5, s. 484-488Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Large vacancy clusters, or voids, formed during growth have been reported in Ge. The divacancy is a precursor to such clusters, and is believed to be stable up to 150 or 180 {ring operator} C. It is also believed to form in Ge irradiated at room temperature where single vacancies are mobile. Density functional theory calculations have been performed to calculate the energy barriers for migration and dissociation of the divacancy. We find the binding energy in the neutral charge state to lie in the range 1.1-1.5 eV, and this increases for more negative charge states. The migration energies were found to vary from 1.0 to 1.3 eV from the singly positive to the doubly negative state

  • 108.
    Fujita, N.
    et al.
    School of Physics, University of Exeter.
    Blumenau, A.T.
    Max-Planck-Institut für Eisenforschung GmbH.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Theoretical studies on ‹100› dislocations in single crystal CVD diamond2006Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 203, nr 12, s. 3070-3075Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dislocations are common defects in both natural as well as in CVD-grown diamond. Recent advances in the growth of high quality single crystal CVD diamond have led to an increased interest in the atomistic and electronic structure of ‹100› dislocations. These dislocations are observed as mixed-type 45° and pure edge dislocations. Hence in this work we present ab initio modelling studies on these two types of dislocations. The 45° dislocation is found to be by far more stable than the pure edge and both dislocations lead to states in the electronic band gap. An alternative structure for the mixed-type dislocation, which is not straight but kinked and consists of short edge and screw segments, was found slightly higher in energy than the straight structure.

  • 109.
    Sque, S.J.
    et al.
    School of Physics, University of Exeter.
    Jones, Robert
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Theoretical study on the adsorption of armchair carbon nanotubes on the hydrogenated surface of diamond2006Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 203, nr 12, s. 3107-3113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles density-functional theory has been used to investigate the interaction of (metallic) (7,7) carbon nanotubes with the hydrogenated (001) surface of diamond. There is no evidence for a significant chemical interaction between the nanotubes and the diamond surface, although an appreciable binding energy is obtained. The corresponding electronic band structures are indicative of moderate electron transfer from the diamond substrate to the nanotube, which would in practice leave behind a mobile layer of holes. These results suggest that carbon nanotubes may, like buckminsterfullerene, act as suitable p-type transfer dopants for diamond.

  • 110.
    Sque, S.J.
    et al.
    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.
    School of Natural Science, University of Newcastle upon Tyne.
    Transfer doping of diamond: Buckminsterfullerene on hydrogenated, hydroxylated, and oxygenated diamond surfaces2006Ingår i: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 17, nr 6, s. 459-465Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A monolayer of buckminsterfullerene (C60) has been modelled on hydrogenated, hydroxylated (-OH-terminated), and oxygenated diamond surfaces using ab-initio, density-functional-theory calculations, with a view to assessing the likelihood of transfer doping in each case. The C60 layer is predicted to spontaneously extract electrons from the hydrogenated surface, although on the hydroxylated surface there is an energy gap of ~1 eV preventing a similar electron transfer. With the fully oxygenated surface, there is a gap to electron transfer of ~4 eV, effectively prohibiting the transfer-doping effect. In each case, the molecule causes only very little disturbance to the substrate, although chemical reaction remains a significant possibility

  • 111.
    Sque, S.J.
    et al.
    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.
    University of Newcastle Upon Tyne.
    Transfer doping of diamond: the use of C60 and C60F36 to effect p-type surface conductivity2006Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 376, s. 268-71Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio density-functional theory is used to determine the suitability for transfer doping of diamond surfaces with various hydrogen and oxygen terminations. Transfer doping of the hydrogenated (0 0 1) diamond surface with C60 is investigated, and electron transfer from diamond to C60 (leaving a hole layer near the diamond surface) is predicted for a C60 coverage of about one monolayer. The efficiency of electron transfer is expected to increase for higher coverages. It is also shown that the greater electron affinity of fluorinated C60 is likely to enhance the effect, in that C60F36 can extract electrons from hydrogenated diamond at much lower coverages. The consequences of oxygenation of the diamond surface on the transfer-doping properties of C60 are also investigated

  • 112.
    Fujita, N.
    et al.
    Department Physik, Universität Paderborn.
    Jones, R.
    School of Physics, University of Exeter.
    Goss, J.P.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Frauenheim, T.
    Department Physik, Universität Paderborn.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Diffusion of nitrogen in silicon2005Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 87, nr 2, s. 21902-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 113.
    Markevich, V.P.
    et al.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Murin, L.I.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Lastovskij, S.B.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Medvedeva, L.R.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Lindström, J.L.
    Lund University, Division of Solid State Physics.
    Peaker, A.R.
    Centre for Electronic Materials, Devices and Nanostructures, University of Manchester.
    Coutinho, J.
    Department of Physics, University of Aveiro, Campus Santiago.
    Jones, R.
    School of Physics, University of Exeter.
    Torres, V.J.B.
    Department of Physics, University of Aveiro, Campus Santiago.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Electronic properties and structure of a complex incorporating a self-interstitial and two oxygen atoms in silicon2005Ingår i: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 108, s. 273-278Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic properties and structure of a complex incorporating a self-interstitial (I) and two oxygen atoms are presented by a combination of deep level transient spectroscopy (DLTS), infrared absorption spectroscopy and ab-initio modeling studies. It is argued that the IO2 complex in Si can exist in four charge states (IO2-, IO20, IO2+, and IO2++). The first and the second donor levels of the IO2 complex show an inverted location order in the gap, leading to a E(0/ ++) occupancy level at Ev + 0.255 eV. Activation energies for hole emission, transformation barriers between different structures, and positions of LVM lines for different configurations and charge states have been determined. These observables were calculated by density-functional calculations, which show that they are accounted for if we consider at least two charge-dependent defect structures.

  • 114.
    Coutinho, J.
    et al.
    Department of Physics, University of Aveiro, Campus Santiago.
    Jones, R.
    School of Physics, University of Exeter.
    Torres, V.J.B.
    Department of Physics, University of Aveiro, Campus Santiago.
    Barroso, M.
    Department of Physics, University of Aveiro, Campus Santiago.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Electronic structure and Jahn-Teller instabilities in a single vacancy in Ge2005Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, nr 48, s. L521-L527Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional modelling studies of the single vacancy in large Ge clusters are presented. We take a careful look at the origin of Jahn-Teller instabilities as a function of the vacancy net charge, resulting in a variety of structural relaxations. By comparing electron affinities of the vacancy with those from defects with well established gap states, we were able to estimate three acceptor states for the vacancy at E(-/0) ≤ Ev+0.2 eV, E(≤/-) ≤ Ec-0.5 eV and eV. As opposed to the Si vacancy, the defect in Ge is not a donor. We also show that these dissimilarities have fundamental consequences for the electronic/atomic picture of other centres, such as transition metals in germanium crystals.

  • 115.
    Sque, S.J.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Goss, J.P.
    Physics Centre, School of Natural Sciences, University of Newcastle upon Tyne.
    Briddon, P.R.
    Physics Centre, School of Natural Sciences, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    First-principles study of C60 and C60F36 as transfer dopants for p-type diamond2005Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, nr 2, s. L21-L26Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio density-functional-theory has been used to investigate transfer doping between C60 monolayers and the hydrogenated (100) diamond surface. An electron transfer from diamond to C60 is predicted for a C60 coverage of around one monolayer, and the possibility of electron transfer is expected to increase for higher coverages, leading to an accumulation of holes at the diamond surface. It has been found that the greater electron affinity of fluorinated C60 is likely to enhance the effect. Results are reported on the structural and electronic properties of isolated C60 and C60F36 molecules, solid C60, and a monolayer of each material adjacent to the (100)-(2 × 1):H diamond surface.

  • 116.
    Eberlein, T.A.G.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School 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.
    Grown-in and radiation-induced defects in 4H-SiC2005Ingår i: Semiconductor defect engineering: materials, synthetic structures and devices : symposium held March 28 - April 1 2005, San Francisco, California, U.S.A. ; [Symposium E, held at the 2005 MRS spring meeting] / [ed] S. Ashok, Warrendale, Pa: Materials Research Society, 2005, s. 3-13Konferensbidrag (Refereegranskat)
    Abstract [en]

    SiC is a material that seems ideal for high-power, high frequency and high temperature electronic devices. It does not suffer from large reverse recovery inefficiencies typical for silicon when switching. In contrast to silicon. SiC is however difficult to dope by diffusion, and instead ion-implantation is used to achieve selective area doping. The drawback of this technique is that irradiating the crystal with dopant atoms creates a great, deal of lattice damage including vacancies, interstitials, antisites and impurity-radiation defect complexes. Although many of the point defects can be eliminated through thermal annealing, some however, e.g. the photoluminescence (PL) D1 and DLTS Z1/Z2 centers in 4H-SiC, are stable to high temperatures. In this polytype, D1 and the related alphabet lines are the most prominent PL signals. The latter can be seen directly after low energy irradiation while D1 usually dominates the PL spectrum of implanted and irradiated SiC after annealing. Not only implantation but also rapid growth of SiC by CVD methods leads to a deterioration in quality with an increase in electrically active grown in defects. Among these, the Z1/Z2 defects are dominant in n-type 4H-SiC. as well as material that has been exposed to radiation. We use first principles density functional calculations to investigate defect models for the above mentioned defects in 4H-SiC and relate their electrical and optical activity to experiments

  • 117.
    Coutinho, J.
    et al.
    Department of Physics, University of Aveiro, Campus Santiago.
    Torres, V.J.B.
    Department of Physics, University of Aveiro, Campus Santiago.
    Pereira, R.N.
    Institut for Fysik og Astronomi, Århus Universitet.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Local vibrations on hydrogen dimers in dilute SiGe crystalline solutions2005Ingår i: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 124/125, nr Suppl., s. 363-367Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Atomic hydrogen is a concomitant impurity in semiconductors. Its presence in Si, Ge and SiGe alloys has been established by means of paramagnetic resonance, optical, electrical and theoretical modeling studies. Hydrogen self-trapping is known to occur in Si and Ge, resulting in the formation of molecular hydrogen and H2* interstitial dimers. Here we report on the properties of H22* complexes in dilute SiGe alloys, by using an ab initio density functional method. It is found that these complexes form preferentially within Si-rich regions. H2* dimers in Si-rich alloys show vibrational properties similar to those in pure Si. On the other hand, in Ge-rich material the minority Si atoms act as nucleation sites, with the consequent formation of at least one preferential H2*- Si defect variant, showing a distinct vibrational activity.

  • 118.
    Hounsome, L.S.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Martineau, P.M.
    DTC, Maidenhead.
    Shaw, M.J.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Blumenau, A.T.
    Max-Planck-Institut für Eisenforschung GmbH.
    Fujita, N.
    School of Physics, University of Exeter.
    Optical properties of vacancy related defects in diamond2005Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 202, nr 11, s. 2182-2187Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ‹110› vacancy chains, multi-vacancy clusters and vacancy discs have been modeled using density functional theory within the AIMPRO and DFTB codes. While a connection can be established between the results on vacancy chains and previous EPR experiments, no connection can be made between the point defects and the optical properties of natural type IIa brown diamonds. However, a vacancy disc consisting of a {111} double plane of vacancies is stable and possesses an absorption spectrum similar to that found in brown diamonds.

  • 119.
    Latham, Chris
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Alatalo, M.
    Department of Electrical Engineering, Lappeenranta University of Technology.
    Nieminen, R.M.
    Laboratory of Physics, Helsinki University of Technology.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Passivation of copper in silicon by hydrogen2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 23Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structures and energies of model defects consisting of copper and hydrogen in silicon are calculated using the AIMPRO local-spin-density functional method. For isolated copper atoms, the lowest energy location is at the interstitial site with Td symmetry. Substitutional copper atoms are found to adopt a configuration with D2d symmetry. We conclude that the symmetry is lowered from Td due to the Jahn-Teller effect. Interstitial hydrogen atoms are found to bind strongly to substitutional copper atoms with an energy that is more than the difference in formation energy over the interstitial site for Cu. The resulting complex has C2v symmetry in the -2 charge state where the H atom is situated about 1.54 Å away from the Cu atom in a [100] direction. In other charge states the symmetry of the defect is lowered to Cs or C1. A second hydrogen atom can bind to this complex with nearly the same energy as the first. Two structures are found for copper dihydride complexes that have nearly equal energies; one with C2 symmetry, and the other with Cs symmetry. The binding energy for a third hydrogen atom is slightly more than for the first. Calculated electronic levels for the model defects relative to one another are found to be in fair to good agreement with experimental data, except for the copper-dihydride complex. The copper trihydride complex has no deep levels in the bandgap, according to our calculations.

  • 120.
    Blumenau, A.T.
    et al.
    Max-Planck-Institut für Eisenforschung GmbH.
    Eberlein, T.A.G.
    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.
    Frauenheim, T.
    Theoretische Physik, Universität Paderborn.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    The effect of charge on kink migration at 90° partial dislocations in SiC2005Ingår i: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 202, nr 5, s. 877-882Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    SiC bipolar devices show a degradation under forward-biased operation which has been linked with a recombination enhanced motion of one of the two glide dislocations having either Si or C core atoms. We have carried out calculations of the core structures and dynamics of partial dislocations in 3C and 2H-SiC using the density functional based codes DFTB and AIMPRO. After in earlier theoretical work we reported on the structure, energetics and electronic activity of both of the Shockley partials, and on the formation and migration barriers of kinks, in this work we present first results on the effect of charge on the disloction kinks. The calculations give insights into the device degradation mechanism.

  • 121.
    Fujita, N.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Goss, J.P.
    School of Natural Science, University of Newcastle upon Tyne.
    Frauenheim, T.
    Department of Physics, University of Paderborn.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Theoretical investigations of the diffusion of nitrogen-pair defects in silicon2005Ingår i: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 108, s. 407-12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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

  • 122.
    Jones, R.
    et al.
    School of Physics, University of Exeter.
    Carvalho, A.
    Department of Physics, University of Aveiro.
    Coutinho, J.
    Department of Physics, University of Aveiro.
    Torres, V.J.B.
    Department of Physics, University of Aveiro.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Theoretical investigations of the energy levels of defects in germanium2005Ingår i: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 108-109, s. 697-702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The donor and acceptor levels of defects in Ge as well as in Si are found using a local density functional method applied to large H-terminated defective clusters. The surfaces of the clusters are modified so that their band gaps are aligned with experimental values. It is shown that the resulting energies of the first donor and acceptor levels are within about 0.2 eV of the experimental values

  • 123.
    Adey, J.
    et al.
    School of Physics, University of Exeter.
    Palmer, D.W,
    School of Physics, University of Exeter.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Theory of boron-vacancy complexes in silicon2005Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, nr 16, s. 165211-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The substitutional boron-vacancy BsV complex in silicon is investigated using the local density functional theory. These theoretical results give an explanation of the experimentally reported, well established metastability of the boron-related defect observed in p-type silicon irradiated at low temperature and of the two hole transitions that are observed to be associated with one of the configurations of the metastable defect. BsV is found to have several stable configurations, depending on charge state. In the positive charge state the second nearest neighbor configuration with C1 symmetry is almost degenerate with the second nearest neighbor configuration that has C1h symmetry since the bond reconstruction is weakened by the removal of electrons from the center. A third nearest neighbor configuration of BsV has the lowest energy in the negative charge state. An assignment of the three energy levels associated with BsV is made. The experimentally observed Ev+0.31 eV and Ev+0.37 eV levels are related to the donor levels of second nearest neighbor BsV with C1 and C1h symmetry respectively. The observed Ev+0.11 eV level is assigned to the vertical donor level of the third nearest neighbor configuration. The boron-divacancy complex BsV2 is also studied and is found to be stable with a binding energy between V2 and Bs of around 0.2 eV. Its energy levels lie close to those of the V2. However, the defect is likely to be an important defect only in heavily doped material.

  • 124. Iwata, H.P.
    et al.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P R
    Department of Physics, University of Newcastle.
    An ab initio study of intrinsic stacking faults in GaN2004Ingår i: Proceedings of the 10th International Conference on Silicon Carbide and Related Materials, Stafa-Zuerich: Trans Tech Publications Inc., 2004, s. 1617-1620Konferensbidrag (Refereegranskat)
    Abstract [en]

    A first-principles study of intrinsic stacking faults in GaN is reported. Our calculations are based on density functional theory in local density approximation. We have found that the electron wave functions belonging to the conduction and valence band edge states tend to be localized almost exclusively on different sides of the faulted layer. We suggest that the electrostatic field caused by the macroscopically polarized 2H-GaN parts below and above a thin 3C-like layer around the stacking fault is responsible for these possibly shallow localized states.

  • 125.
    Adey, J.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Palmer, D.W.
    School of Physics, University of Exeter.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Degradation of boron-doped Czochralski-grown silicon solar cells2004Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, nr 5, s. 055504-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The formation mechanism and properties of the boron-oxygen center responsible for the degradation of Czochralski-grown Si(B) solar cells during operation is investigated using density functional calculations. We find that boron traps an oxygen dimer to form a bistable defect with a donor level in the upper half of the band gap. The activation energy for its dissociation is found to be 1.2 eV. The formation of the defect from mobile oxygen dimers, which are shown to migrate by a Bourgoin mechanism under minority carrier injection, has a calculated activation energy of 0.3 eV. These energies and the dependence of the generation rate of the recombination center on boron concentration are in good agreement with observations.

  • 126.
    Blumenau, A.T.
    et al.
    Department of Physics, Faculty of Science, University of Paderborn.
    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.
    Frauenheim, T.
    Department of Physics, University of Newcastle.
    Density functional based modelling of 30° partial dislocations in SiC2004Ingår i: Proceedings of the 10th International Conference on Silicon Carbide and Related Materials, ICSCRM 2003, Stafa-Zuerich: Trans Tech Publications Inc., 2004, Vol. 1, s. 453-456Konferensbidrag (Refereegranskat)
    Abstract [en]

    Experiment has shown that 4H- and 6H-SiC pin diodes degrade rapidly during forward biased operation. This degradation is accompanied by the formation and expansion of stacking faults in the basal plane. It is believed that the observed rapid stacking fault growth is due to a recombination-enhanced dislocation glide (REDG) mechanism at the bordering partial dislocations. In our work we investigate the structure and properties of basal plane 30° Shockley partials in SiC by means of density functional based calculations. Barriers to their glide motion, and thus the expansion of the accompanying stacking fault is modelled in a process involving the formation and subsequent migration of kinks in the dislocation. In combination with an analysis of the electronic structure of the partials and stacking faults, this allows an identification of those types of partials which will be affected by the REDG mechanism in this model.

  • 127.
    Blumenau, A.T.
    et al.
    Universität Paderborn.
    Frauenheim, T.
    Universität Paderborn.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Willems, B.
    University of Antwerp.
    Tendeloo, G. van
    University of Antwerp.
    Dislocation structures in diamond: density-functional based modelling and high-resolution electron microscopy2004Ingår i: Diffusion and defect data, solid state data. Part A, Defect and diffusion forum, ISSN 1012-0386, E-ISSN 1662-9507, Vol. 226-228, s. 11-30Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The core structures of perfect 60° and edge dislocations in diamond are investigated atomistically in a density-functional based tight-binding approach, and their dissociation is discussed both in terms of structure and energy. Furthermore, high resolution electron microscopy is performed on dislocation cores in high-temperature, high-pressure annealed natural brown diamond, and HRTEM image simulation allows a comparison of theoretically predicted and experimentally observed structures.

  • 128.
    Goss, J.P.
    et al.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Eberlein, T.A.G.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Pinho, N.
    School of Physics, University of Exeter.
    Blumenau, A.T.
    Theoretische Physik, Universität Paderborn.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Electrical and optical properties of rod-like defects in silicon2004Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 85, nr 20, s. 4633-4635Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 129. Adey, J
    et al.
    Jones, R
    Palmer, D W
    Briddon, P R
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Erratum: Degradation of Boron-Doped Czochralski-Grown Silicon Solar Cells [Phys. Rev. Lett., 93, 055504 (2004)]2004Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 93, nr 16, s. 169904-Artikel i tidskrift (Övrigt vetenskapligt)
  • 130.
    Prezzi, D.
    et al.
    School of Physics, University of Exeter.
    Eberlein, T.A.G.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Hourahine, B.
    Theoretische Physik, Universität Paderborn.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hydrogen-related photoluminescent centers in SiC2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 20, s. 205207-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local density functional calculations are used to investigate models of the center responsible for a prominent set of luminescent lines with zero-phonon lines around 3.15 eV in hydrogen rich 4H-SiC and previously attributed to VSi-H . We find that the electronic structure of this defect and the character of its vibrational modes are inconsistent with this assignment. In contrast, a H2* center, bound to a carbon anti-site, is more stable than the isolated molecule and possesses a donor level close to that observed for the H-lines. Moreover, its vibrational modes are in good agreement with experiment. A possible mechanism for the radiation enhanced quenching of the defect is discussed.

  • 131.
    Prezzi, D.
    et al.
    School of Physics, University of Exeter.
    Eberlein, T.A.G.
    School of Physics, University of Exeter.
    Filhol, J.S.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Shaw, M.J.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Optical and electrical properties of vanadium and erbium in 4H-SiC2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, nr 19, s. 193202-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Local-density-functional calculations are carried out on vanadium and erbium centers in 4H-SiC. Particular attention is paid to their electrical and optical properties. We find that both V and Er lie at Si sites and can exist in three charge states with deep donor and acceptor levels. While isolated VSi possesses intra-d and ionization induced optical transitions around 0.94 and 2.9 eV respectively, the intense and temperature stable intra-f optical transitions due to Er are unlikely to be due to an isolated Er defect. It is suggested that both impurities can trap H and N forming complexes which may limit the electrical efficiency of V and act as Er related exciton traps.

  • 132.
    Coutinho, J.
    et al.
    Department of Physics, University of Aveiro.
    Jones, R.
    School of Physics, University of Exeter.
    Shaw, M.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Optically active erbium-oxygen complexes in GaAs2004Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 84, nr 10, s. 1683-1685Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Density functional modeling of Er and Er-O complexes in GaAs show that Er impurities at the Ga site are not efficient channels for exciton recombination, but decorative O atoms play crucial roles in inhibiting Er precipitation and in creating the necessary conditions for electron-hole capture. Among the defects studied, the ErGaOAs and ErGa(OAs)2 models have the symmetry and carrier trap location close to the defect responsible for the strong 1.54 µm photoluminescence band in Er, O codoped GaAs.

  • 133.
    Jones, R.
    et al.
    School of Physics, University of Exeter.
    Hahn, I.
    School of Physics, University of Exeter.
    Goss, J.P.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Structure and electronic properties of nitrogen defects in silicon2004Ingår i: Gettering and Defect Engineering in Semiconductor Technology GADEST 2003: proceedings of the 10th International Autumn Meeting, Trans Tech Publications Inc., 2004, s. 93-98Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 134.
    Markevich, V.P.
    et al.
    Centre for Electronic Materials, University of Manchester Institute of Science and Technology.
    Peaker, A.R.
    Centre for Electronic Materials, University of Manchester Institute of Science and Technology.
    Coutinho, J.
    Department of Physics, University of Aveiro.
    Jones, R.
    School of Physics, University of Exeter.
    Torres, V.J.B.
    Department of Physics, University of Aveiro.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Murin, L.I.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Dobaczewski, L.
    Institute of Physics, Polish Academy of Sciences.
    Abrosimov, N.V.
    Institute of Crystal Growth, Berlin.
    Structure and properties of vacancy-oxygen complexes in Si1-xGex alloys2004Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 69, nr 12, s. 125218-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electronic properties and structure of vacancy-oxygen (VO) complexes in Czochralski-grown Si1-xGex crystals (0

  • 135.
    Goss, J.P.
    et al.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    The lattice location of Ni in diamond: a theoretical study2004Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, nr 25, s. 4567-4578Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 136.
    Iwata, H.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    A new type of quantum wells: stacking faults in silicon carbide2003Ingår i: Microelectronics Journal, ISSN 0959-8324, Vol. 34, nr 5, s. 371-374Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on a new type of quantum wells with the width as thin as 10 Å, which are composed of SiC only, and consequently have ideal interfaces. These quantum wells are actually stacking faults in SiC. Certain types of stacking faults in SiC polytypes create small 3C-like regions, where the stacking sequences along the c-axis become locally cubic in the hexagonal host crystals. Since the conduction band offsets between the cubic and hexagonal polytypes are very large with the conduction band minima of 3C-SiC lower than that of the other polytypes, such thin 3C inclusions can introduce locally lower conduction bands, thus acting as quantum films perpendicular to the c-axis. One mechanism for the occurrence of stacking faults in the perfect SiC single crystals is the motion of partial dislocations in the basal planes, the partial dislocations leaving behind stacking fault regions.

  • 137.
    Iwata, H.P.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Ab initio study of 3 C inclusions and stacking fault-stacking fault interactions in 6H-SiC2003Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, nr 8, s. 4972-4979Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ab initio supercell calculations of cubic inclusions in 6H-SiC are performed. The cubic inclusions can be created in perfect 6H-SiC by the propagation of successive partial dislocations having the same Burgers vector in neighboring basal planes, i.e., multiple stacking faults. We have studied the electronic structures and the total energies of 6H-SiC single crystals that contain one, two, three, and four stacking faults, based on density functional theory in local density approximation. Our total energy calculations have revealed that the second stacking fault energy in 6H-SiC is about six to seven times larger than that of an isolated stacking fault, which is actually opposite the trend recently obtained for 4H-SiC [J. Appl. Phys. 93, 1577 (2003)]. The effects of spontaneous polarization on the electronic properties of stacking disorders are examined in detail. The calculated positions of the quantum-well-like localized bands and stacking fault energies of 3C inclusions in 6H-SiC are compared with those previously determined in 4H-SiC, and the possibility of local hexagonal to cubic polytypic transformations is discussed in light of the formation energy and quantum-well action.

  • 138.
    Blumenau, A.T.
    et al.
    Department of Physics, Universität Paderborn.
    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.
    Frauenheim, T.
    Department of Physics, Universität Paderborn.
    Basal plane partial dislocations in silicon carbide2003Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 340, s. 160-164Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Under operating conditions (forward bias) bipolar 4H- and 6H-SiC devices are known to degrade rapidly through stacking fault formation and expansion in the basal plane. It has been suggested that a recombination-enhanced dislocation glide (REDG) mechanism allows the bordering Shockley partial dislocations to overcome their barrier to glide motion and thus results in the observed stacking fault growth. In this work, we investigate the structure and properties of the participating Shockley partials by means of density functional-based atomistic calculations. Their glide motion is modelled in a process involving the formation and subsequent migration of kinks. This in combination with an analysis of the electronic structure of the partials allows an identification of those types which will be affected by the REDG mechanism.

  • 139.
    Latham, Chris
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Nieminen, R.M.
    Laboratory of Physics, Helsinki University of Technology.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Calculated properties of nitrogen-vacancy complexes in beryllium- and magnesium-doped GaN2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 20, s. 205209-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The properties of defect complexes consisting of a nitrogen vacancy with a substitutional beryllium or magnesium atom on neighboring lattice sites in hexagonal GaN are calculated using the AIMPRO local-density-functional theory method. Both types of defects VN-BeGa and VN-MgGa are bound with respect to their isolated constituents. They do not appear to have any electronic levels in the bandgap, and are expected to be neutral defects. Important structural differences are found. In its minimum energy configuration, the Be atom in the VN-BeGa complex lies nearly in the same plane as the three equivalent N atoms nearest to it. Thus, it has shorter Be-N bonds than the Ga-N distance in the bulk crystal, while the Mg atom in the VN-MgGa complex occupies a position closer the lattice site of the Ga atom it replaces. Hence, the VN-BeGa complex has a larger open volume than the VN-MgGa complex. This is consistent with positron annihilation experiments [Saarinen et al., J. Cryst. Growth 246, 281 (2002); Hautakangas et al., Phys. Rev. Lett. 90, 137402 (2003)]. The frequency of the highest local vibrational mode of the VN-BeGa center is calculated to be within 3-4 % of an infrared absorption line detected in Be-doped GaN

  • 140.
    Latham, Chris D.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Nieminen, R.M.
    Laboratory of Physics, Helsinki University of Technology.
    Fall, C.J.
    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.
    Physics Centre, School of Natural Sciences, University of Newcastle upon Tyne.
    Calculated properties of point defects in Be-doped GaN2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, nr 20, s. 205206-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The properties of several point defects in hexagonal gallium nitride that can compensate beryllium shallow acceptors (BeGa) are calculated using the AIMPRO method based on local density functional theory. BeGa itself is predicted to have local vibrational modes (LVM's) very similar to magnesium acceptors. The highest frequency is about 663 cm-1. Consistent with other recent studies, we find that interstitial beryllium double donors and single-donor beryllium split interstitial pairs at gallium sites are very likely causes of compensation. The calculations predict that the split interstitial pairs possess three main LVM's at about 1041, 789, and 738 cm-1. Of these, the highest is very close to the experimental observation in Be-doped GaN. Although an oxygen donor at the nearest-neighboring site to a beryllium acceptor (BeGa-ON) is also a prime suspect among defects that are possibly responsible for compensation, its highest frequency is calculated to be about 699 cm-1 and hence is not related in any way to the observed center. Another mode for this defect is estimated to be about 523 cm-1 and is localized on the ON atom. These two vibrations of BeGa-ON are thus equivalent to those for the isolated substitutional centers perturbed by the presence of their impurity partners.

  • 141.
    Iwata, H.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Cubic polytype inclusions in 4H-SiC2003Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, nr 3, s. 1577-1585Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multiple stacking faults in 4H-SiC, leading to narrow 3C polytype inclusions along the hexagonal c direction, have been studied using an ab initio supercell approach with 96 atoms per supercell. The number of neighboring stacking faults considered is two, three, and four. The wave functions and the two-dimensional energy bands, located in the band gap and associated with the narrow inclusions, can be reconciled with a planar quantum-well model with quantum-well depth equal to the conduction band offset between 3C- and 4H-SiC. We show that the existence of the electronic dipole moment due to the spontaneous polarization leads to a clear asymmetry of the bound wave functions inside the quantum well, and that the perturbation associated with the change in the dipole moment caused by the 3C-like inclusion accounts for the appearance of very shallow localized states at the valence band edge. We have also calculated the stacking fault energies for successive stacking faults. It is found that the stacking fault energy for two stacking faults in adjacent basal planes is reduced by approximately a factor of 4 relative to that of one isolated stacking fault, indicating that double stacking faults in 4H-SiC could be quite common.

  • 142.
    Coutinho, J.
    et al.
    Department of Physics, University of Aveiro.
    Andersen, O.
    Center for Electronic Materials, Devices and Nanostructures, University of Manchester.
    Dobaczewski, L.
    Institute of Physics, Polish Academy of Sciences.
    Nielsen, K. Bonde
    Institute of Physics and Astronomy, University of Aarhus.
    Peaker, A.R.
    Center for Electronic Materials, Devices and Nanostructures, University of Manchester.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Effect of stress on the energy levels of the vacancy-oxygen-hydrogen complex in Si2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 18, s. 184106-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The piezospectroscopic properties of the VOH defect in Si are found using stress Laplace deep level transient spectroscopy (DLTS) and are compared with local density-functional calculations of (i) the acceptor level and its shift under stress, and (ii) the alignment of the neutral center under stress. The theory is able to account for two acceptor levels observed for 〈100〉, 〈111〉, and 〈110〉 stress even though additional splitting is expected for a defect with static C1h symmetry. This is related to (i) a rapid reorientation of the H atom within the defect at temperatures at which the DLTS experiments are carried out, and (ii) the small effect of stress on two orientations of the defect under 〈110〉 stress. The theory is also able to give a quantitative account of the alignment of the center. The effect of stress on the reorientation barrier of the defect is also investigated. The reorientation barrier of the defect in its positive charge state is found theoretically to be very small, consistent with the lack of any splitting in the donor level under stress.

  • 143.
    Iwata, H.
    et al.
    Department of Physics & Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics Technology, Linköping University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Effective mass of electrons in quantum-well-like stacking-fault gap states in silicon carbide2003Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 433-436, s. 519-522Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A first-principles calculation of the effective mass of electrons in quantum-well-like gap states induced by stacking faults and cubic inclusions in 4H- and 6H-SiC is performed, based on the density functional theory in the local density approximation. Our calculated effective electron masses for perfect crystals are in very good agreement with those previously determined both theoretically and experimentally. It has been found that electrons confined in the thin 3C-like regions have clearly heavier effective masses than that in perfect 3C-SiC.

  • 144.
    Iwata, H.P.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.H.
    Department of Physics, University of Newcastle.
    Effective masses of two-dimensional electron gases around cubic inclusions in hexagonal silicon carbide2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 24, s. 245309-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The main purpose of this article is to determine the two-dimensional effective mass tensors of electrons confined in thin 3C wells in hexagonal SiC, which is a first step in the understanding of in-plane electron motion in the novel quantum structures. We have performed ab initio band structure calculations, based on the density functional theory in the local density approximation, for single and multiple stacking faults leading to thin 3C-like regions in 4H- and 6H-SiC and deduced electron effective masses for two-dimensional electron gases around the cubic inclusions. We have found that electrons confined in the thin 3C-like layers have clearly heavier effective masses than in the perfect bulk 3C-SiC single crystal.

  • 145.
    Iwata, H.
    et al.
    Department of Physics, Linköping University.
    Lindefelt, U.
    Department of Physics, Linköping University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Electronic properties of stacking faults in 15R-SiC2003Ingår i: Silicon carbide and related materials: ECSCRM 2002 : proceedings of the 4th European Conference on Silicon Carbide and Related Materials, September 2-5, 2002, Linköping, Sweden, Uetikon-Zuerich: Trans Tech Publications Inc., 2003, s. 531-534Konferensbidrag (Refereegranskat)
    Abstract [en]

    A first-principles calculation of stacking faults in 15R-SiC is reported. All the geometrically distinguishable stacking faults which can be introduced by the glide of partial dislocations in (0001)-basal planes are investigated: there exist as many as five different stacking faults in 15R-SiC. Electronic properties and stacking fault energies of these extended defects are studied based on the density functional theory in the local density approximation. Stacking fault energies are also calculated using the axial next nearest neighbor Ising (ANNNI) model.

  • 146.
    Markevich, V.P.
    et al.
    Centre for Electronic Materials, University of Manchester.
    Peaker, A.R.
    Centre for Electronic Materials, University of Manchester.
    Murin, L.I.
    Institute of Solid State and Semiconductor Physics, Minsk.
    Coutinho, J.
    Department of Physics, University of Aveiro.
    Torres, V.J.B.
    Department of Physics, University of Aveiro.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Auret, F.D.
    Centre for Electronic Materials, University of Manchester.
    Abrosimov, N.V.
    Institute of Crystal Growth, Berlin.
    Electronic properties of vacancy-oxygen complexes in SiGe alloys2003Ingår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 340, s. 790-4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Capacitance transient techniques, combined with ab initio modeling, were employed to study the electronic properties and structure of vacancy-oxygen (VO) complexes in unstrained Czochralski-grown Si1-xGex crystals (0

  • 147.
    Coutinho, J.
    et al.
    Department of Physics, University of Aveiro.
    Torres, V.J.B.
    Department of Physics, University of Aveiro.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Electronic structure of divacancy-hydrogen complexes in silicon2003Ingår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, nr 39, s. S2809-S2814Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Divacancy-hydrogen complexes (V2H and V2H2) in Si are studied by ab initio modelling using large supercells. Here we pay special attention to their electronic structure, showing that these defects produce deep carrier traps. Calculated electrical gap levels indicate that V2H2 is an acceptor, whereas V2H is amphoteric, with levels close to those of the well known divacancy. Finally our results are compared with the available data from deep level transient spectroscopy and electron paramagnetic resonance experiments.

  • 148.
    Iwata, H.
    et al.
    Department of Physics & Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics Technology, Linköping University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Electronic structure of twin boundaries in 3C-SiC, Si and diamond2003Ingår i: Silicon carbide and related materials 2002: ECSCRM 2002 ; proceedings of the 4th European Conference on Silicon Carbide and Related Materials, September 2 - 5, 2002, Linköping, Sweden / [ed] Peder Bergman; Erik Janzén, Uetikon-Zuerich: Trans Tech Publications Inc., 2003, s. 527-30Konferensbidrag (Refereegranskat)
    Abstract [en]

    We report on a first-principles band structure calculation of twin boundaries in 3C-SiC, Si, and diamond, based on the density functional theory in the local density approximation. It is found that the electron wave functions belonging to the conduction and valence band edge states in 3C-SiC tend to be localized almost exclusively on different sides of the boundaries, while there is no such feature in Si and diamond. We have interpreted these localization and segregation phenomena as a consequence of the electrostatic field caused by the spontaneous polarization due to the hexagonal symmetry around twin boundaries. A mechanism for the creation of twin boundaries, i.e., propagation of partial dislocations in neighboring basal planes, has been investigated using total energy calculations, and it has been realized that the double-intrinsic-stacking-fault structure in 3C-SiC, coinciding with the extrinsic stacking faults, is much energetically favored.

  • 149.
    Iwata, H.P.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Energies and electronic properties of isolated and interacting twin boundaries in 3C-SiC, Si, and diamond2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 11, s. 113202-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principles calculations of twin boundaries in 3C-SiC, Si, and diamond are performed, based on the density-functional theory in the local density approximation. We have investigated the formation energies and electronic properties of isolated and interacting twin boundaries. It is found that in 3C-SiC, interacting twin boundaries which are separated by more than two Si-C bilayers are actually energetically more favorable, implying a relatively frequent appearance of these defects. The effect of the spontaneous polarization associated with the hexagonal symmetry around twin boundaries is also studied, and we have observed that the wave functions belonging to the conduction- and valence-band edge states in 3C-SiC tend to be localized almost exclusively on different sides of the faulted layers, while there is no such feature in Si or diamond.

  • 150.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Coomer, B.J.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Fall, C.J.
    School 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.
    Extended defects in diamond: the interstitial platelet2003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, nr 16, s. 165208-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

123456 101 - 150 av 288
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf