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| 2. |
- Nylandsted Larsen, A., et al.
(författare)
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Tin-vacancy acceptor levels in electron-irradiated n-type silicon
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:7, s. 4535-4544
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Tidskriftsartikel (refereegranskat)abstract
- Si crystals (n-type, fz) with doping levels between 1.5×1014 and 2×1016 cm-3 containing in addition ∼1018 Sn/cm3 were irradiated with 2-MeV electrons to different doses and subsequently studied by deep level transient spectroscopy, Mössbauer spectroscopy, and positron annihilation. Two tin-vacancy (Sn-V) levels at Ec-0.214 eV and Ec-0.501 eV have been identified (Ec denotes the conduction band edge). Based on investigations of the temperature dependence of the electron-capture cross sections, the electric-field dependence of the electron emissivity, the anneal temperature, and the defect-introduction rate, it is concluded that these levels are the double and single acceptor levels, respectively, of the Sn-V pair. These conclusions are in agreement with electronic structure calculations carried out using a local spin-density functional theory, incorporating pseudopotentials to eliminate the core electrons, and applied to large H-terminated clusters. Thus, the Sn-V pair in Si has five different charge states corresponding to four levels in the band gap.
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| 3. |
- Hoffmann, L., et al.
(författare)
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Substitutional carbon in Ge and Si1-xGex
- 1997
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Ingår i: Defects in semiconductors. - : Trans Tech Publications Inc.. ; , s. 97-102
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Konferensbidrag (refereegranskat)abstract
- In the present work, carbon is implanted into monocrystalline Ge and into relaxed epitaxial MBE-grown Si1-xGex. The samples are studied with infrared absorption spectroscopy along with ion-channeling studies on the Ge samples. Finally, ab-initio local density functional cluster theory is applied to calculate the structure and the local vibrational modes of substitutional carbon, Cs, in Ge. After implantation of 12C+ in Ge at room temperature and subsequent annealing at 350°C, a sharp absorption line is observed at 531 cm-1. By isotope substitution, it is concluded that the 531 cm-1 line represents a local vibrational mode of a single carbon atom. From ion-channeling measurements on samples annealed at 450°C, it is found that 31±3 % of the carbon atoms are located at substitutional sites. The population of the substitutional site and the intensity of the 531 cm-1 mode have identical annealing behavior and it is concluded that the 531 cm-1 mode is the three-dimensional T2 stretch mode of Cs in Ge. The calculated frequency and isotope shift for this mode are in good agreement with the observations. In Si0.65Ge0.35, two broad absorption lines are observed at ∼551 and ∼592 cm-1 after implantation of 12C+ and subsequent annealing at 550°C. From measurements on samples implanted with 13C+ and coimplanted with 12C+ and 13C+ we conclude that these lines represent local vibrational modes of defects containing a single carbon atom. In 13C+ implanted Si1-xGex samples that contain 15 to 50 % Ge a number of modes are observed in a frequency range from ∼510 to ∼610 cm-1, i.e., in the range of Cs in Ge and in Si. From the experimental findings it is concluded that substitutional carbon in Si1-xGex binds to both Si and Ge.
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| 4. |
- Janson, M S, et al.
(författare)
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Diffusion of dopants and impurities in device structures of SiC, SiGe and Si
- 2001
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Ingår i: DIFFUSIONS IN MATERIALS. ; , s. 597-609
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Konferensbidrag (refereegranskat)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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| 5. |
- Larsen, A. Nylandsted, et al.
(författare)
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E center in silicon has a donor level in the band gap
- 2006
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 97:10, s. 106402/1-106402/4
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Tidskriftsartikel (refereegranskat)abstract
- It has been an accepted fact for more than 40 years that the E center in Si (the group-V impurity-vacancy pair)-one of the most studied defects in semiconductors-has only one energy level in the band gap: namely, the acceptor level at about 0.45 eV below the conduction band. We now demonstrate that it has a second level, situated in the lower half of the band gap at 0.27 eV above the valence band. The existence of this level, having a donor character, is disclosed by a combination of different transient-capacitance techniques and electronic-structure calculations. The finding seriously questions some diffusion-modeling approaches performed in the past.
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