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Sökning: WFRF:(NORDELL N)

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1.
  • Doyle, J. P., et al. (författare)
  • Electrically active point defects in n-type 4H–SiC
  • 1998
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 84:3, s. 61-68
  • Tidskriftsartikel (refereegranskat)abstract
    • An electrically active defect has been observed at a level position of ∼ 0.70 eV below the conduction band edge (Ec) with an extrapolated capture cross section of ∼ 5×10−14 cm2 in epitaxial layers of 4H–SiC grown by vapor phase epitaxy with a concentration of approximately 1×1013 cm−3. Secondary ion mass spectrometry revealed no evidence of the transition metals Ti, V, and Cr. Furthermore, after electron irradiation with 2 MeV electrons, the 0.70 eV level is not observed to increase in concentration although three new levels are observed at approximately 0.32, 0.62, and 0.68 eV below Ec with extrapolated capture cross sections of 4×10−14, 4×10−14, and 5×10−15 cm2, respectively. However, the defects causing these levels are unstable and decay after a period of time at room temperature, resulting in the formation of the 0.70 eV level. Our results suggest strongly that the 0.70 eV level originates from a defect of intrinsic nature. The unstable behavior of the electron irradiation-induced defects at room temperature has not been observed in the 6H–SiC polytype.
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  • Bowallius, O., et al. (författare)
  • Scanning capacitance microscopy investigations of SiC structures
  • 2001
  • Ingår i: Materials Science in Semiconductor Processing. - 1369-8001 .- 1873-4081. ; 4:03-jan, s. 209-211
  • Tidskriftsartikel (refereegranskat)abstract
    • We have applied scanning capacitance microscopy (SCM) to investigate SIC structures grown by vapour-phase epitaxy. The SCM technique is evaluated using n- and p-type doping staircase structures with doping concentrations ranging from 10(16) to 10(20) cm(-3). The n- and p-type doping was obtained by doping SiC with nitrogen and aluminium, respectively. The sample cross-sections for SCM were obtained by simple cleaving. For doping levels above 10(17) cm(-3) the SCM data are consistent with doping data obtained independently from secondary ion mass spectroscopy (SIMS). Treating the samples with diluted hydrofluoric acid significantly improves the SCM signal for the low-doped regions. The SCM technique has been used to investigate doping redistribution in patterned regrowth of n- and p-type SIC around dry-etched mesas. In both cases, contrast variations were seen close to the mesa walls, indicative of doping variations; lower and higher incorporation for p- and n-type, respectively. The observations are shown to be consistent with the expected trends in dopant incorporation in the SiC material.
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  • Doyle, J P, et al. (författare)
  • Observation of near-surface electrically active defects in n-type 6H-SiC
  • 1998
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 83, s. 3649-3651
  • Tidskriftsartikel (refereegranskat)abstract
    • In n-type 6H-SiC epitaxial layers grown by vapor phase epitaxy, we find that in contrast to the majority of the epitaxial layer, where electrically active defects are observed with a concentration less than 1 X 10(-13) cm(-3), a region near the front surface contains defects with concentrations approaching 10(14) cm(-3). A relationship between the near-surface defects and metallic impurities is suggested by a Ti concentration of 1 X 10(16) cm(-3) in this region. The high concentration of near surface defects is found to significantly reduce the carrier lifetime. (C) 1998 American Institute of Physics. [S0021-8979(98)03007-2].
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  • Hemmingsson, Carl, 1964-, et al. (författare)
  • Deep-Level Defects in Electron-irradiated 4H SiC Epitaxial Layers
  • 1997
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 81:9, s. 6155-6159
  • Tidskriftsartikel (refereegranskat)abstract
    • Deep level defects in electron-irradiated 4H SiC epitaxial layers grown by chemical vapor deposition were studied using deep level transient spectroscopy. The measurements performed on electron-irradiated p+n junctions in the temperature range 100–750 K revealed several electron traps and one hole trap with thermal ionization energies ranging from 0.35 to 1.65 eV. Most of these defects were already observed at a dose of irradiation as low as ≈5×1013 cm-2. Dose dependence and annealing behavior of the defects were investigated. For two of these electron traps, the electron capture cross section was measured. From the temperature dependence studies, the capture cross section of these two defects are shown to be temperature independent. © 1997 American Institute of Physics.
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  • Janson, M. S., et al. (författare)
  • Transient enhanced diffusion of implanted boron in 4H-silicon carbide
  • 2000
  • Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:11, s. 1434-1436
  • Tidskriftsartikel (refereegranskat)abstract
    • Experimental evidence is given for transient enhanced diffusion of boron (B) in ion-implanted silicon carbide (SiC). The implanted B is diffusing several mu m into the samples when annealed at 1600 and 1700 degrees C for 10 min, but the in-diffused tails remain unaffected when the annealing times are increased to 30 min at the same temperatures. A lower limit of the effective B diffusivity at 1600 degrees C is determined to 7x10(-12) cm(2)/s, which is 160 times larger than the equilibrium B diffusivity given in the literature.
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  • Kassamakova, L, et al. (författare)
  • Al/Si ohmic contacts to p-type 4H-SiC for power devices
  • 2000
  • Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 338-3, s. 1009-1012
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of Al/Si/p-4H SiC ohmic contacts at temperatures as low as 750 degreesC is reported in this paper. The dependence of electrical properties and contact morphology have been investigated as a function of the annealing regime in the interval 600-700 degreesC. The lowest contact resistivity of 3.8x10(-5) Omega .cm(2) was obtained at 700 degreesC annealing, however the most reproducible results were in the low 10(-4) Omega .cm(2) range. It has been established that the predominate current transport mechanism in the Al/Si/SiC contacts is thermionic-field emission. Atomic force microscopy showed that the addition of Si to the contact layer improves its morphology, and the pitting of annealed Al is not observed. The contacts developed are stable during ageing at 500 degreesC and at operating temperatures up to 450 degreesC. After the contacts testing with current density of 10(3) A/cm(2) at temperatures up to 450 degreesC, their contact resistivity decreases slightly.
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  • Kassamakova, L, et al. (författare)
  • Study of the electrical, thermal and chemical properties of Pd ohmic contacts to p-type 4H-SiC : dependence on annealing conditions
  • 1999
  • Ingår i: Materials Science and Engineering: B. - 0921-5107 .- 1873-4944. ; 61-62, s. 291-295
  • Tidskriftsartikel (refereegranskat)abstract
    • The electrical and chemical properties of Pd ohmic contacts to p-type 4H-SiC, together with their thermal stability, have been studied in the annealing temperature range 600–700°C. The ohmic behaviour of as-deposited and annealed contacts has been checked from I–V characteristics and the contact resistivity has been determined by the linear TLM method in order to determine the electrical properties and the thermal stability. An ohmic behaviour was established after annealing at 600°C, while the lowest contact resistivity 5.5×10−5 Ω.cm2 was obtained at 700°C. The contact structure, before and after annealing, was investigated using X-ray photoelectron spectroscopy depth analysis. As-deposited Pd films form an abrupt and chemically inert Pd/SiC interface. Annealing causes the formation of palladium silicide. After formation at 600°C the contact structure consists of unreacted Pd and Pd3Si. During annealing at 700°C, Pd and SiC react completely and a mixture of Pd3Si, Pd2Si and C in a graphite state is found in the contact layer. The examination of the thermal stability shows that after a 100 h heating at 500°C, only the contacts annealed at 700°C did not suffer from a change in resistivity. This can be explained by a more complete reaction between the Pd contact layer and the SiC substrate at this higher annealing temperature.
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  • Kassamakova, L, et al. (författare)
  • Temperature stable Pd ohmic contacts to p-type 4H-SiC formed at low temperatures
  • 1999
  • Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 46:3, s. 605-611
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of low resistivity Pd-based ohmic contacts to p-type 4H-SiC below 750 degrees C are reported herein, The electrical properties of the contacts were examined using I-V measurements and the transmission-line model (TLM) technique. Contact resistivity as a function of annealing was investigated over the temperature range of 600 degrees C-700 degrees C, The lowest contact resistivity (5.5 x 10(-5) Ohm cm(2)) was obtained after annealing at 700 degrees C for 5 min, Atomic force microscopy of the as-deposited Pd layer showed a root-mean square roughness of similar to 8 nm, while after annealing at 700 degrees C, agglomeration occurred, increasing the roughness to 111 nm, Auger electron spectroscopy depth profiles revealed that with annealing, interdiffusion had resulted in the formation of Pd-rich silicides. However, X-ray diffraction and Rutherford backscattering showed that the majority of the film was still (unreacted) Pd. The thermal stability and reliability of the Pd contacts were examined by aging and temperature dependence electrical tests, The contacts annealed at 700 OC were stable at prolonged heating at a constant temperature of 500 degrees C and they showed thermal stability in air at operating temperatures up to 450 degrees C, This stability was not found for contacts formed at lower temperatures of 600 degrees C or 650 degrees C.
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  • Kassamakova, L, et al. (författare)
  • Thermostable ohmic contacts on p-type SiC
  • 1998
  • Ingår i: SILICON CARBIDE, III-NITRIDES AND RELATED MATERIALS, PTS 1 AND 2. - 0878497900 ; , s. 787-790
  • Konferensbidrag (refereegranskat)
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  • Linnarsson, M K, et al. (författare)
  • Deuterium incorporation in acceptor doped epitaxial layers of 6H-SiC
  • 1998
  • Ingår i: SILICON CARBIDE, III-NITRIDES AND RELATED MATERIALS, PTS 1 AND 2. ; , s. 761-764
  • Konferensbidrag (refereegranskat)abstract
    • Deuterium is introduced in boron doped epitaxial layers of 6H-SiC by implantation of 30 keV H-2(+) ions in order to form a diffusion source. The samples were subsequently annealed in vacuum at 700 degrees C/16h, 800 degrees C/4h and 900 degrees C/4h. Using depth profiling by secondary ion mass spectrometry (SIMS), the distributions of deuterium at different levels of boron doping are studied. The deuterium concentration correlates with the boron concentration and at a level of similar to 10(18) cm(-3) a ratio H-2/B-11 larger than 0.5 is obtained. From capacitance-voltage (CV) measurements a decrease in the electrical carrier concentration by 50% is revealed after deuterium diffusion at 800 degrees C/4h. At 900 degrees C passivation of the boron accepters ceases but the H-2 atoms are still confined to the boron-doped regions and display no long range migration.
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  • Linnarsson, M K, et al. (författare)
  • Diffusion of light elements in 4H-and 6H-SiC
  • 1999
  • Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 61-2, s. 275-280
  • Tidskriftsartikel (refereegranskat)abstract
    • Deuterium and lithium were introduced in p-type SiC by implantation of 20 keV H-2(+) or 30 keV Li-7(+) ions in order to form a diffusion source. The samples were subsequently annealed in vacuum in the temperature range 400-700 degrees C for 0.25 to 16 h. Secondary ion mass spectrometry (SIMS) was used to measure the deuterium and the lithium distribution after heat treatments. Both deuterium and lithium readily decorate the bombardment-induced defects in the vicinity of the ion implantation profile and they are also trapped, most likely by residual boron impurities, during diffusion into the bulk. An effective diffusion coefficient, reflecting the dissociation of trapped lithium, with an activation energy of 2.1 eV is extracted for lithium diffusion in p-type 6H SIG. Furthermore, a capture radius for trapping (most likely by boron) of deuterium is estimated as 10 Angstrom. (C) 1999 Elsevier Science S.A. All rights reserved.
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  • Nordell, N., et al. (författare)
  • Control of Al and B doping transients in 6H and 4H SiC grown by vapor phase epitaxy
  • 1997
  • Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 26:3, s. 187-192
  • Tidskriftsartikel (refereegranskat)abstract
    • The atomic concentration profiles in 4H and 6H SiC created by Al and B doping turn-on and turn-off during vapor phase epitaxy (VPE) was investigated by secondary ion mass spectrometry (SIMS). It was found that dopant traces were adsorbed to the reactor walls and re-evaporated after the dopant precursor flow was switched off. This adsorption/re-evaporation process limits the doping dynamic range to about three orders of magnitude for Al, and two orders of magnitude for B. An order of magnitude in doping dynamics could be gained by simultaneously switching the gases and changing the C:Si precursor ratio. By adding a 10 min growth interruption with an H or HC1 etch at the doping turn-off, the background doping tail could be considerably suppressed. In total, a doping dynamics for Al of almost five orders of magnitude can be controlled within a 30 nm layer. For B, the dynamic range is more than three orders of magnitude, and the abruptness is most probably diffusion limited. Abackground doping level of 2 × 1015 cm−3 for Al and 2 × 1016 cm−3 for B was obtained. For Al, the background doping is most probably due to the adsorption/re-evaporation of dopants at the reactor walls; while for B, the background doping may in addition be limited by diffusion.
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  • Schoner, A, et al. (författare)
  • Hall effect investigations of 4H-SiC epitaxial layers grown on semi-insulating and conducting substrates
  • 1999
  • Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 61-2, s. 389-394
  • Tidskriftsartikel (refereegranskat)abstract
    • Nitrogen- and aluminum-doped 4H silicon carbide epitaxial layers were grown simultaneously on semi-insulating and conducting substrates. The layers were investigated by conventional van der Pauw Hall effect measurements and for comparison also with secondary ion mass spectrometry and capacitance voltage measurements. It was found, that the carrier concentration in the layers grown on conducting substrates were overestimated by the Hall effect measurement, which leads to an underestimation of the ionization energy of the main dopant, as compared to the layer grown on semi-insulating substrates. The difference can be explained by a two-layer Hall effect model. (C) 1999 Elsevier Science S.A. All rights reserved.
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  • Schoner, A, et al. (författare)
  • Hydrogen incorporation in epitaxial layers of 4H- and 6H-silicon carbide grown by vapor-phase epitaxy
  • 1997
  • Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 6, s. 1293-1296
  • Tidskriftsartikel (refereegranskat)abstract
    • The incorporation of hydrogen during vapor phase epitaxy was investigated using secondary ion mass spectroscopy, low temperature photoluminescence, and capacitance-voltage measurements. It was found that hydrogen incorporation is strongly dependent on the concentration of the acceptor dopants aluminum and boron, regardless of changes in the doping concentration caused by varying the concentration ratio between carbon and silicon or the dopant precursor flow. An electrical passivation of the acceptor dopants was found and could be reduced by annealing at temperatures above 1000 degrees C. At the same anneal temperature hydrogen-related photoluminescence was considerably reduced and the diffusion of hydrogen was detected. (C) 1997 Elsevier Science S.A.
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