| 1. |
- Doyle, J. P., et al.
(författare)
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Characterization of deep level defects in 4H and 6H SiC via DLTS, SIMS and MeV e-beam irradiation
- 1996
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Ingår i: III-nitride, SiC and diamond materials for electronic devices. ; , s. 519-524
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Konferensbidrag (refereegranskat)abstract
- Electrically active defects in both 4H and 6H polytypes of SiC have been observed through the use of deep level transient spectroscopy (DLTS). Schottky contacts were grown by VPE with doping concentrations, the epitaxial layer having a doping concentration in the range of 10 exp 14/cu cm to 10 exp 17/cu cm. Numerous levels have been found in the as-grown n-type 6H-SiC samples, and SIMS and MeV electron irradiation have been employed to correlate the defect levels to impurities or structural defects. In contrast, only a single level is observed in the as-grown 4H-SiC samples.
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| 2. |
- Doyle, J. P., et al.
(författare)
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Electrically active point defects in n-type 4H–SiC
- 1998
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 84:3, s. 61-68
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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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| 3. |
- Linnarsson, Margareta K., et al.
(författare)
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Cascade mixing in AlxGa1-xAs/GaAs during sputter profiling by noble-gas ions
- 1999
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 60:20, s. 14302-14310
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Tidskriftsartikel (refereegranskat)abstract
- The effect of cascade mixing on profile broadening during secondary-ion mass spectrometry (SIMS) analysis has been thoroughly investigated for AlxGa1-xAs/GaAs structures of five different compositions (x=0.1, 0.3, 0.5, 0.73, or 1) and layers with varying thicknesses (from one monolayer to 1000 Å). The SIMS analyses were performed using primary sputtering ions of 20Ne+, 40Ar+, 84Kr+, and 136Xe+ with an impact energy (E) ranging from 1.8 to 13.2 keV and an angle of incidence, with respect to the surface normal (θ), from 62° to 35°. Within the experimental accuracy, the decay length of the trailing edge was found to be proportional to E1/2cosθ where the proportionality constant displays a relatively weak dependence on primary ion mass. However, the leading edge is strongly affected by the extension of the collision cascade as demonstrated by a comparison of the results for the different ions at a given energy. As long as the cascade is fully developed before reaching an interface no dependence on the sample depth is obtained for the profile broadening. Furthermore, the decay length for the trailing edges is extracted in the dilute limit and no effect of the marker thickness or the x value is revealed. A numerical treatment of the profile broadening within a diffusional model, where the diffusion coefficient is assumed to be proportional to the energy deposited in elastic collisions, gives a surprisingly good agreement with the experimental data.
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| 4. |
- Linnarsson, Margareta K., et al.
(författare)
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Diffusion of hydrogen in 6H silicon carbide
- 1996
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Ingår i: III-nitride, SiC and diamond materials for electronic devices. ; , s. 625-630
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 6H polytype silicon carbide (SiC) samples of n-type have been implanted with 50-keV H(+) ions and subsequently annealed at temperatures between 200 and 1150 C. Using depth profiling by secondary ion mass spectrometry, the motion of hydrogen is observed in the implanted region for temperatures above 700 C. A diffusion coefficient of about 10 exp -14 sq cm/s is extracted at 800 C with an approximate activation energy of about 3.5 eV. Hydrogen displays strong interaction with the implantation-induced defects, and stable hydrogen-defect complexes are formed. These complexes anneal out at temperatures in excess of 900 C, and are tentatively identified as carbon-hydrogen centers at a Si vacancy.
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| 5. |
- Timpka, Toomas, et al.
(författare)
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Long-term economic effects of team-based clinical case management of patients with chronic minor disease and long-term absence from working life
- 1997
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Ingår i: Scandinavian Journal of Social Medicine. - : SAGE Publications. - 0300-8037. ; 25:4, s. 229-237
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: To examine the socio-economic effects of team-based clinical case management of patients with chronic minor disease bound for early retirement.Design: Marginal analysis of programme costs and benefits to society compared with no-programme baseline of costs occurring in society due to productivity loss. Prospective patient data collection on admission, discharge, and at one year and five years after discharge to determine programme effectiveness.Setting: Out-patient clinic at the department of social medicine in tertiary care hospital.Subjects: 239 patients with minor disease and long-term vocational absence consecutively admitted to the study. At the one-year evaluation, 17 patients had been readmitted to the team, 7 could not be found, 6 declined the interview and 2 were deceased. At the five-year evaluation of 49 patients who were active after one year, one was deceased and 10 were unable to be found.Main outcome measures: Vocational activity. Programme costs. Benefits to society measured by decrease in indirect costs.Results: The one-year vocational rehabilitation rate from the program was 20.5% and the five-year rehabilitation rate was 11.3%. The total discounted cost for case management of the 239 patients was 7.6 MSEK (£600,000). The decrease in the indirect costs to society from the 28 patients found active after five years was 35.1 MSEK (£2,500,000). The net present value of the programme at the 1991 price level was 27.5 MSEK (£2,365,000).Conclusions: Tertiary care level team-based clinical case management for vocational rehabilitation of patients with chronic minor disease has a positive cost-benefit ratio. A cross-boundary awareness at a health policy level is needed of the societal costs involved for this group of patients who fall between the traditional services in health care and social work.
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