| 1. |
- Galeckas, Augustinas, et al.
(författare)
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Investigation of stacking fault formation in hydrogen bombarded 4H-SiC
- 2005
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2004. - 0878499636 ; , s. 327-330
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Konferensbidrag (refereegranskat)abstract
- The effects of hydrogen and proton irradiation on stacking fault formation in 4H-SiC are investigated by an optical pump-probe method of imaging spectroscopy. We report optically stimulated nucleation and expansion of stacking faults (SFs) in 0.6 keV H-2(+) implanted n-/n+ and p+/n-/n+ structures. The activation enthalpy for recombination enhanced dislocation glide (REDG) in hydrogenated samples (∼ 0.25 eV) is found to be similar to that in a virgin material. Our results indicate that SFs mainly nucleate at the internal n-/n+ interface, beyond reach of hydrogen, thus justifying minor SF passivation effect. No REDG could be initiated optically in 2.5 MeV proton irradiated samples due to radiation defects providing alternative recombination channels to bypass the REDG mechanism. The radiation damage was verified by DLTS, revealing several new levels below E-C in the range 0.4-0.80 eV, and by PL, showing the onset of D-center related luminescence band and concurrent increase of the nonradiative recombination rate.
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| 2. |
- Kortegaard Nielsen, Hanne
(författare)
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Capacitance transient measurements on point defects in silicon and silicol carbide
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrically active point defects in semiconductor materials are important because they strongly affect material properties like effective doping concentration and charge carrier lifetimes. This thesis presents results on point defects introduced by ion implantation in silicon and silicon carbide. The defects have mainly been studied by deep level transient spectroscopy (DLTS) which is a quantitative, electrical characterization method highly suitable for point defect studies. The method is based on measurements of capacitance transients and both standard DLTS and new applications of the technique have been used. In silicon, a fundamental understanding of diffusion phenomena, like room-temperature migration of point defects and transient enhanced diffusion (TED), is still incomplete. This thesis presents new results which brings this understanding a step closer. In the implantation-based experimental method used to measure point defect migration at room temperature, it has been difficult to separate the effects of defect migration and ion channeling. For various reasons, the effect of channeling has so far been disregarded in this type of experiments. Here, a very simple method to assess the amount of channeling is presented, and it is shown that channeling dominates in our experiments. It is therefore recommended that this simple test for channeling is included in all such experiments. This thesis also contains a detailed experimental study on the defect distributions of vacancy and interstitial related damage in ion implanted silicon. Experiments show that interstitial related damage is positioned deeper (0.4 um or more) than vacancy related damage. A physical model to explain this is presented. This study is important to the future modeling of transient enhanced diffusion. Furthermore, the point defect evolution in low-fluence implanted 4H-SiC is investigated, and a large number of new defect levels has been observed. Many of these levels change or anneal out at temperatures below 300 C, which is not in accordance with the general belief that point defect diffusion in SiC requires high temperatures. This thesis also includes an extensive study on a metastable defect which we have observed for the first time and labeled the M-center. The defect is characterized with respect to DLTS signatures, reconfiguration barriers, kinetics and temperature interval for annealing, carrier capture cross sections, and charge state identification. A detailed configuration diagram for the M-center is presented.
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| 3. |
- Kortegaard Nielsen, Hanne, et al.
(författare)
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Capacitance transient study of the metastable M center in n-type 4H-SiC.
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:8
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Tidskriftsartikel (refereegranskat)abstract
- The metastable M center in n-type 4H silicon carbide is studied in detail after it has been introduced by 2.5 MeV proton irradiation with a fluence of 1x10(12) cm(-2). The experimental procedures included deep-level transient spectroscopy, carrier capture coefficient and capacitance versus temperature measurements, and pulse-train measurements. The pulse-train measurements are reproduced by simulations. Three band-gap levels have previously been assigned to the M center: M-1 at E-C-0.42 eV, M-2 at E-C-0.63 eV, and M-3 at E-C-0.83 eV, where E-C is the conduction-band edge. Direct measurements of the majority-carrier capture cross sections show that the cross section values extracted from Arrhenius plots are about two orders of magnitude too large, indicating a large entropy factor. A detailed configuration diagram of the M center is presented, including charge state levels and reconfiguration barriers. Evidence in support of a fourth M center level, not explicitly observed, is presented. Isochronal and isothermal annealing experiments show that the M center anneal out between 310 and 370 degrees C in a process displaying first-order kinetics. The annealing process, which is shown to have an activation energy of 2.0 eV, is identified as dissociation.
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| 4. |
- Kortegaard Nielsen, Hanne, et al.
(författare)
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M-center in low-dose proton implanted 4H-SiC; Bistability and change in emission rate
- 2005
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2004. ; , s. 497-500
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Konferensbidrag (refereegranskat)abstract
- 4H-SiC schottky diodes have been implanted with 2.5 MeV protons to a dose of 1 x 10(12) cm(-2) and measured by deep level transient spectroscopy (DLTS). Between annealings at 150 ° C and 200 ° C the whole DLTS-spectra shift in temperature, most clearly revealed for the Z and M-center levels. The shift corresponds to a decrease in emission rate at a given temperature by approximately a factor of 5. It is speculated that the reason for this change in emission rate is to be found in the surrounding material rather than in the defects themselves.
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