| 1. |
- Hallen, A, et al.
(author)
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Implanted p(+)n-junctions in silicon carbide
- 2003
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In: APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY. ; , s. 653-657
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Conference paper (peer-reviewed)abstract
- Ion implantation is considered a key technology for the realisation of silicon carbide electronic devices. Here we will give an overview of the field and present some recent results of ion implanted 4H SiC epitaxial layers. Mainly Al ions of keV energies have been used at different fluence, flux and target temperature. The samples have been investigated by secondary ion mass spectrometry (SIMS), channeling Rutherford backscattering (RBS-c) and transmission electron microscopy (TEM), both as-implanted and after annealing up to 1900 degreesC. Also the electrical activation of Al-implanted and annealed material has been investigated by scanning spreading resistance microscopy (SSRM). The damage accumulation, monitored by RBS-c, is linear with ion fluence but depends strongly on implantation temperature and ion flux. Annealing at temperatures above 1700 degreesC is needed to remove the damage and to electrically activate implanted Al ions. At these high annealing temperatures, however, dislocation loops are formed that have a negative influence on device performance.
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| 2. |
- Janson, M S, et al.
(author)
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Channeled implants in 6H silicon carbide
- 2000
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In: SILICON CARBIDE AND RELATED MATERIALS - 1999 PTS, 1 & 2. ; , s. 889-892
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Conference paper (peer-reviewed)abstract
- Implants of MeV B-11, Al-27 and Ga-69 into the <0001> channel of 6H-SiC have been performed and concentration versus depth profiles have been obtained utilizing secondary ion mass spectrometry (SIMS). The experiment shows that the deepest channeled Ga ions reach a depth of 6.6 mum, which is 4 times deeper than the projected range of a random angle implantation, while the deepest channeled B ions only exceed the random projected range by 40%. Measurements at several implantation fluences show that implantation induced damage quench the deep channeling at fluences around 2 and 10x10(13) cm(-2) for Al and Ga, respectively, while only a minor fluence dependence is found in the B implants at fluences up to 2.6x10(14) cm(-2). The ion mass dependence of these effects is explained by the electronic to nuclear stopping ratios. Monte Carlo simulations of the channeling implants have also been performed and good agreements are found between simulations and experimental data.
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| 3. |
- Janson, M S, et al.
(author)
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Diffusion of dopants and impurities in device structures of SiC, SiGe and Si
- 2001
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In: DIFFUSIONS IN MATERIALS. ; , s. 597-609
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Conference paper (peer-reviewed)abstract
- Silicon Carbide (SiC) has a high thermal stability and for most elements temperatures in excess of 2000 degreesC are anticipated to reach reasonable diffusivities (greater than or equal to 10(-13) cm(2)/s). We demonstrate, however, that light elements, like hydrogen and lithium, exhibit a considerable mobility already at less than or equal to 400 degreesC, Technologically, the principal interest in these light elements arises because of their ability to electrically passivate shallow acceptors and donors as well as deep level defects in common semiconductors (SiC, Si, GaAs). Indeed, for both hydrogen and lithium the diffusion kinetics is shown to be strongly affected by trapping and de-trapping at boron impurities in the SiC layers. Evidence is also provided that hydrogen migrates as a positively charged ion in p-type SiC. Furthermore, similar to that in crystalline silicon, transient enhanced diffusion of ion-implanted boron is observed in SiC. The initial boron diffusivity during postimplant annealing at 1600 degreesC is enhanced by more than two orders of magnitude compared to equilibrium conditions. For Silicon Germanium (SiGe) diffusion of the n-type dopants Sb and P is studied. Comparing results from strained and relaxed SiGe layers annealed under inert and oxidizing conditions it is unambiguously shown that the diffusion of Sb is almost exclusively mediated by vacancies. On the other hand, P diffusion is predominantly assisted by Si self-interstitials and in this case compositional and strain effects in the SiGe layers are competing.
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| 4. |
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| 5. |
- Kuznetsov, A. Y., et al.
(author)
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Self-interstitial migration during ion irradiation of boron delta-doped silicon
- 2000
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In: Materials Science in Semiconductor Processing. - 1369-8001 .- 1873-4081. ; 3:4, s. 279-283
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Journal article (peer-reviewed)abstract
- Boron delta layers in silicon, grown by molecular beam epitaxy and characterized by the secondary ion mass spectrometry, have been employed to investigate the migration of silicon self-interstitials during irradiation with MeV protons in the 500-850 degreesC temperature range. After growth, the samples were thinned from the backside to a thickness that made them transparent for the proton energies used. As a result, the generation rate of point defects can be considered as essentially uniform throughout the samples. However: the evolution of the boron profiles is almost identical to that observed after injection of self-interstitials caused by thermal oxidation of the samples at elevated temperature. This strongly indicates that the surface acts as a reflective boundary for the migrating self-interstitials or/ and an efficient sink for mobile vacancies. Furthermore, higher value of interstitial supersaturation in the near-surface region in proton-irradiated samples is consistent with experimentally detected depth dependence for immobile fraction in boron clusters. Then, activation energy of boron mobilization, (0.9 +/- 0.4) eV, was attributed to the dissociation of boron clusters.
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| 6. |
- Portavoce, A, et al.
(author)
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Sb lattice diffusion in Si1-xGex/Si(001) heterostructures : Chemical and stress effects
- 2004
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:15, s. 155415-
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Journal article (peer-reviewed)abstract
- The Sb diffusion coefficient in Si1-xGex/Si1-yGey(001) heterostructures grown by molecular beam epitaxy (MBE) was measured for temperatures ranging from 700 to 850 degreesC, Ge composition from 0 to 20 % and biaxial pressure from -0.8 (tension) to 1.4 GPa (compression). A quantitative separation of composition and biaxial stress effects is made. We show that the Sb lattice diffusion coefficient: (i) increases with Ge concentration in relaxed layers or at constant biaxial pressure and (ii) increases with compressive biaxial stress and decreases with tensile biaxial stress at constant Ge composition. The enhancement of Sb lattice diffusion in Si1-xGex layers in epitaxy on Si(001) is thus due to the cooperative effect of Ge composition and induced compressive biaxial stress. However, the first effect (composition) is predominant. The activation volume of Sb diffusion in Si1-xGex layers is deduced from the variation of the Sb diffusion coefficients with biaxial pressure. This volume is negative. The sign of the activation volume, its absolute value and its variation with temperature confirm the prediction of the thermodynamic model proposed by Aziz, namely, that under a biaxial stress the activation volume is reduced to the relaxation volume.
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| 7. |
- Spiers, H, et al.
(author)
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Self propagating high temperature synthesis of magnesium zinc ferrites (MgxZn1-xFe2O3): thermal imaging and time resolved X-ray diffraction experiments
- 2004
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In: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501. ; 14:7, s. 1104-1111
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Journal article (peer-reviewed)abstract
- Spinel ferrites of the form MgxZn1-xFe2O4 ( x = 0. 0.25, 0.50, 0.75, 1.00) were prepared by self-propagating high-temperature synthesis (SHS) from reactions of iron(III), zinc and magnesium oxides, iron powder and sodium perchlorate. The driving force for the reactions is the oxidation of iron powder. Reactions were carried out in the presence of an external magnetic field of 0.2 or 1.1 T. Reaction velocity and temperatures were obtained by thermal imaging camera. The transformation of reactants to products was studied by time resolved X-ray diffraction using Rietveld refinement for determination of phase percentages. Reactions typically reached temperatures in excess of 1150 degreesC with a timescale of complete conversion of reactant to products of 20 s. All materials were characterised by X-ray powder diffraction (XRD), energy dispersive X-ray analysis (EDXA), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Mossbauer spectroscopy and vibrating sample magnetometry (VSM).
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