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- 1. Phys. Rev. B 77, 195204 (2008) , “Identification of antisite carbon split-interstitial defects in 4H-SiC”, J. W. Steeds, W. SullivanA rich variety of optical centers with high energy local vibrational modes has been found in electron-irradiated 4H-SiC in both the as-irradiated and annealed states. These energies have been measured and the annealing dependence of the optical centers has been investigated by low-temperature... (Read more)
- 2. Phys. Rev. B 75, 115418 (2007) , “Early stages of radiation damage in graphite and carbon nanostructures: A first-principles molecular dynamics study”, Oleg V. Yazyev, Ivano Tavernelli, Ursula Rothlisberger, and Lothar HelmUnderstanding radiation-induced defect formation in carbon materials is crucial for nuclear technology and for the manufacturing of nanostructures with desired properties. Using first-principles molecular dynamics, we perform a systematic study of the nonequilibrium processes of radiation damage in... (Read more)
- 3. Phys. Rev. B 75, 085208 (2007) , “Clustering of vacancy defects in high-purity semi-insulating SiC”, R. Aavikko, K. Saarinen, F. Tuomisto, B. Magnusson, N. T. Son, and E. JanzénPositron lifetime spectroscopy was used to study native vacancy defects in semi-insulating silicon carbide. The material is shown to contain (i) vacancy clusters consisting of four to five missing atoms and (ii) Si-vacancy-related negatively charged defects. The total open volume bound to the... (Read more)
- 4. Phys. Rev. Lett. 98, 115503 (2007) , “Oxygen Vacancy Clustering and Electron Localization in Oxygen-Deficient SrTiO3: LDA+U Study”, Do Duc Cuong, Bora Lee, Kyeong Mi Choi, Hyo-Shin Ahn, Seungwu Han, and Jaichan LeeWe find, using a local density approximation +Hubbard U method, that oxygen vacancies tend to cluster in a linear way in SrTiO3, a prototypical perovskite oxide, accompanied by strong electron localization at the 3d state of the nearby Ti transition metal ion. The vacancy... (Read more)
- 5. Appl. Phys. Lett. 89, 092113 (2006) , “Large fluorine-vacancy clusters in Si and their capture efficiency for self-interstitials”, Giorgia M. Lopez and Vincenzo FiorentiniBased on ab initio density-functional energetics for saturated (n=2m+2) fluorine-vacancy clusters FnVm for m up to 4, the authors set up a model showing that (a) fluorine-vacancy (FV) aggregates in Si can form in any... (Read more)
- 6. Appl. Phys. Lett. 89, 031116 (2006) , “Er3+ excited state absorption and the low fraction of nanocluster-excitable Er3+ in SiOx”, C. J. Oton, W. H. Loh, and A. J. KenyonDespite the observation by a number of groups of a strong luminescence sensitization effect of erbium ions by excitation exchange from silicon nanoclusters, there is considerable experimental evidence that the fraction of Er ions excited by Si-nc is actually very low for much of the material... (Read more)
- 7. Appl. Phys. Lett. 89, 012505 (2006) , “Diffusion and clustering of substitutional Mn in (Ga,Mn)As”, Hannes Raebiger, Maria Ganchenkova, and Juhani von BoehmThe Ga vacancy mediated microstructure evolution of (Ga,Mn)As during growth and postgrowth annealing is studied using a multiscale approach. The migration barriers for the Ga vacancies and substitutional Mn together with their interactions are calculated using first principles, and temporal... (Read more)
- 8. Phys. Rev. B 74, 245420 (2006) , “Energetics, structure, and long-range interaction of vacancy-type defects in carbon nanotubes: Atomistic simulations”, J. Kotakoski, A. V. Krasheninnikov,, and K. NordlundThe presence of vacancy clusters in carbon nanotubes has been assumed to explain the formation of carbon peapods and the difference between the experimentally measured and theoretical fracture strength of nanotubes. We use atomistic simulations at various levels of theory to study the... (Read more)
- 9. Phys. Rev. B 74, 245411 (2006) , “Vacancy defects and the formation of local haeckelite structures in graphene from tight-binding molecular dynamics”, Gun-Do Lee, C. Z. Wang, Euijoon Yoon, Nong-Moon Hwang, and K. M. HoThe dynamics of multivacancy defects in a graphene layer is investigated by tight-binding molecular dynamics simulations and by first principles calculation. The simulations show that four single vacancies in the graphene layer first coalesce into two double vacancies, each consisting of a... (Read more)
- 10. Phys. Rev. B 74, 235201 (2006) , “Annealing of multivacancy defects in 4H-SiC”, W. E. Carlos, N. Y. Garces, E. R. Glaser, and M. A. FantonThe annealing behavior of defects observed in electron paramagnetic resonance (EPR) and photoluminescence (PL) is discussed. We consider the divacancy (the P6/P7 EPR centers) and a previously unreported EPR center that we suggest is a VC-VSi-VC... (Read more)
- 11. Phys. Rev. B 74, 045217 (2006) , “Vacancy clustering and diffusion in silicon: Kinetic lattice Monte Carlo simulations”, Benjamin P. Haley, Keith M. Beardmore, and Niels Grønbech-JensenDiffusion and clustering of lattice vacancies in silicon as a function of temperature, concentration, and interaction range are investigated by kinetic lattice Monte Carlo simulations. It is found that higher temperatures lead to larger clusters with shorter lifetimes on average, which grow by... (Read more)
- 12. Phys. Rev. B 74, 035208 (2006) , “Ultranarrow photoluminescence transitions of nitrogen cluster bound excitons in dilute GaAsN”, D. Karaiskaj, A. Mascarenhas, M. Adamcyk, E. C. Young, and T. TiedjeHigh resolution photoluminescence spectroscopy on heavily doped GaAs:N reveals the existence of excitons bound to a nitrogen cluster. The observed transitions are exceedingly sharp, similar to those observed for excitons bound to nitrogen pairs in high quality GaAs with the narrowest transition... (Read more)
- 13. Phys. Rev. B 74, 035205 (2006) , “Mechanisms of arsenic clustering in silicon”, F. F. Komarov, O. I. Velichko, V. A. Dobrushkin, and A. M. MironovA model of arsenic clustering in silicon is proposed and analyzed. The main feature of the proposed model is the assumption that negatively charged arsenic complexes play a dominant role in the clustering process. To confirm this assumption, electron density and concentration of impurity atoms... (Read more)
- 14. Phys. Rev. B 73, 033204 (2006) , “Electrical characterization of metastable carbon clusters in SiC: A theoretical study”, A. Gali, N. T. Son, E. JanznFirst-principles calculations carried out in 3C- and 4H-SiC show that small metastable carbon clusters can be created in irradiated SiC. The metastable carbon clusters possess occupation levels in the p-type as well as in the n-type 4H-SiC. Depending on the... (Read more)
- 15. Phys. Rev. B 71, 245203 (2005) , “Electrical Activity of Er and Er-O Centers in Silicon”, D. Prezzi, T. A. G. Eberlein, R. Jones, J. S. Filhol, J. Coutindo, M. J. Shaw, P. R. Briddon.Spin-polarized density functional calculations are carried out on Er and Er-oxygen defects in crystalline Si. We find that the interstitial site is favored but the diffusion barrier of Eri is only 1.9 eV, and inevitably Eri forms complexes with impurities and... (Read more)
- 16. Phys. Rev. B 71, 115204 (2005) , “Electron Spin Resonance Study of Paramagnetic Centers in Neutron-Irradiated Heat-Treated Silicon”, D. Pierreux and A. StesmansElectron spin resonance (ESR) was used to study neutron-induced defects in silicon as functions of anneal temperature Tan. For Tan below 200 °C, the ESR response is dominated by the Si-P3 and Si-P6 spectra, as observed before. At Tan=200 ... (Read more)
- 17. Appl. Phys. Lett. 85, 1538 (2004) , “Observation of fluorine-vacancy complexes in silicon”, P. J. Simpson, Z. Jenei, P. Asoka-Kumar, R. R. Robison, M. E. LawWe show direct evidence, obtained by positron annihilation spectroscopy, for the complexing of fluorine with vacancies in silicon. Both float zone and Czochralski silicon wafers were implanted with 30 keV fluorine ions to a fluence of 2×1014 ions/cm2, and studied in the... (Read more)
- 18. Eur. Phys. J. Appl. Phys. 27, 13-19 (2004) , “Measurement of process-induced defects in Si sub-micron devices by combination of EDMR and TEM”, T. Umeda, A. Toda, Y. MochizukiProcess-induced defects are a serious issue for modern sub-micron Si LSIs. To characterize such defects, two different techniques are useful: electrically detected magnetic resonance (EDMR) and transmission electron microscope (TEM), which can detect small (point) and extended defects, respectively. We applied EDMR and TEM to the issue of defect-induced leakage currents in dynamic-random-access memory (DRAM) cells. For our DRAM samples (a 0.25- μm-rule series), although TEM showed no extended defects, EDMR successfully detected two types of point defects: V2+O x (Si divacancy-oxygen complexes) and larger Si vacancies (at least larger than V6). We confirmed that these defects are the source of DRAM leakage currents. The observed defects were formed by ion implantation processes, but were more thermally stable than those in bulk Si crystals. The origins of this enhanced stability are attributed to the presence of oxygen atoms and a strong mechanical strain in LSIs. To clarify the origin of the complicated strain in LSI structures, we can directly measure the local-strain distribution in DRAM samples by means of convergent-beam electron diffraction (CBED) using TEM, which provides us with a valuable hint for understanding the formation mechanism of process-induced defects. (Read more)
- 19. Phys. Rev. B 70, 245204 (2004) , “Silicon vacancy annealing and DI luminescence in 6H-SiC”, M. V. B. Pinheiro, E. Rauls, U. Gerstmann, S. Greulich-Weber, H. Overhof, and J.-M. SpaethCombining electron paramagnetic resonance measurements with ab initio calculations, we identify the VCCSi(SiCCSi) complex as a second annealing product of the silicon vacancy via an analysis of resolved carbon hyperfine interactions and of... (Read more)
- 20. Phys. Rev. B 70, 235211 (2004) , “Structure and vibrational spectra of carbon clusters in SiC”, Alexander Mattausch, Michel Bockstedte, and Oleg PankratovThe electronic, structural, and vibrational properties of small carbon interstitial and antisite clusters are investigated by ab initio methods in 3C- and 4H-SiC. The defects possess sizable dissociation energies and may be formed via condensation of carbon interstitials, e.g.,... (Read more)
- 21. Phys. Rev. B 70, 195344 (2004) , “Ab initio study of structural and electronic properties of planar defects in Si and SiC”, C. Raffy, J. Furthmüller, J.-M. Wagner, and F. BechstedtWe present ab initio calculations for internal interfaces in Si and SiC. Density-functional calculations within the local-density approximation and the pseudopotential-plane-wave approach are performed to understand the effect of such two-dimensional defects on the electronic properties. We... (Read more)
- 22. Phys. Rev. B 69, 235202 (2004) , “Ab initio study of the annealing of vacancies and interstitials in cubic SiC: Vacancy-interstitial recombination and aggregation of carbon interstitials”, Michel Bockstedte, Alexander Mattausch, and Oleg PankratovThe annealing kinetics of mobile intrinsic defects in cubic SiC is investigated by an ab initio method based on density-functional theory. The interstitial-vacancy recombination, the diffusion of vacancies, and interstitials to defect sinks (e.g., surfaces or dislocations) as well as the... (Read more)
- 23. Phys. Rev. B 69, 045322 (2004) , “Carbon antisite clusters in SiC: A possible pathway to the DII center”, Alexander Mattausch, Michel Bockstedte, and Oleg PankratovThe photoluminescence center DII is a persistent intrinsic defect which is common in all SiC polytypes. Its fingerprints are the characteristic phonon replicas in luminescence spectra. We perform ab initio calculations of vibrational spectra for various defect complexes and... (Read more)
- 24. Phys. Rev. Lett. 93, 255502 (2004) , “Formation of Thermal Vacancies in Highly As and P Doped Si”, V. Ranki and K. SaarinenUsing positron annihilation measurements we observed the formation of thermal vacancies in highly As and P doped Si. The vacancies start to form at temperatures as low as 650 K and are mainly undecorated at high temperatures. Upon cooling the vacancies form stable vacancy-impurity complexes such as... (Read more)
- 25. Phys. Rev. Lett. 93, 245901 (2004) , “Ab Initio Calculations to Model Anomalous Fluorine Behavior”, Milan Diebel, Scott T. Dunhammplanted fluorine is observed to behave unusually in silicon, manifesting apparent uphill diffusion and reducing diffusion and enhancing activation of boron. In order to investigate fluorine behavior, we calculate the energy of fluorine defect structures in the framework of density functional theory. In addition to identifying the ground-state configuration and diffusion migration barrier of a single fluorine atom in silicon, a set of energetically favorable fluorine defect structures were found (FnVm). The decoration of vacancies and dangling silicon bonds by fluorine suggests that fluorine accumulates in vacancy-rich regions, which explains the fluorine redistribution behavior reported experimentally. (Read more)
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