| 1. |
- Bruzzi, M, et al.
(författare)
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Radiation-hard semiconductor detectors for SuperLHC
- 2005
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 541:1-2, s. 189-201
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Tidskriftsartikel (refereegranskat)abstract
- An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.
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| 2. |
- Hoffmann, L., et al.
(författare)
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Weakly bound carbon-hydrogen complex in silicon
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:24, s. 16659-16666
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Tidskriftsartikel (refereegranskat)abstract
- Local vibrational modes of a weakly bound carbon-hydrogen complex in silicon have been identified with infrared-absorption spectroscopy. After implantation of protons at ∼20 K and subsequent annealing at 180 K, two carbon modes at 596 and 661 cm-1, and one hydrogen mode at 1885 cm-1 are observed. The three modes originate from the same complex, which is identified as bond-centered hydrogen in the vicinity of a nearby substitutional carbon atom. Ab initio theory has been applied to calculate the structure and local modes of carbon-hydrogen complexes with hydrogen located at the first, second, and third nearest bond-center site to substitutional carbon. The results support our assignment.
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| 3. |
- Lavrov, E.V., et al.
(författare)
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Combined infrared absorption and modeling study of a dicarbon-dihydrogen defect in silicon
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:19, s. 12859-12867
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Tidskriftsartikel (refereegranskat)abstract
- Crystalline silicon samples doped with carbon were irradiated with electrons and subsequently implanted with protons. Infrared-absorption measurements revealed local modes of hydrogen and carbon at 2967.4, 911.7, and 654.7 cm-1, which originate from the same defect. Measurements on samples codoped with different carbon and hydrogen isotopes showed that the defect contains two equivalent carbon and two equivalent hydrogen atoms. From uniaxial stress measurements, the defect is found to display trigonal symmetry. Ab initio local-density-functional theory was applied to calculate the structure and local vibrational modes of defects with pairs of equivalent carbon and hydrogen atoms. Based on these results, the observed local modes are ascribed to a defect with two adjacent substitutional carbon atoms, each of which binds a hydrogen atom located between the carbon atoms.
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| 4. |
- Lavrov, E. V., et al.
(författare)
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Local vibrational modes of two neighboring substitutional carbon atoms in silicon
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:1, s. 158-165
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Tidskriftsartikel (refereegranskat)abstract
- Infrared absorption measurements on n-type silicon doped with carbon and irradiated with electrons at room temperature have revealed new absorption lines at 527.4 and 748.7 cm-1, which originate from the same defect. The 748.7-cm-1 line is observed only when the sample is cooled in the dark and the spectrum is measured through a low-pass filter with cutoff frequency below 6000 cm-1. Light with frequency above 6000 cm-1 removes this line and generates the 527.4-cm-1 line. Comparison with spectra recorded on irradiated silicon doped with 13C shows that the two lines represent local vibrational modes of carbon. The annealing behavior of the 748.7-cm-1 line is identical to that of the EPR signal originating from the negative charge state of two adjacent substitutional carbon atoms (Cs-Cs)-. The 527.4- and 748.7-cm-1 lines are ascribed to the E modes of Cs-Cs in the neutral and negative charge states, respectively. The structure and local vibrational modes of (Cs-Cs)0 and (Cs-Cs)- have been calculated by ab initio local density functional theory. The calculated structures agree qualitatively with those obtained previously by Hartree-Fock methods, but the calculated Si-C and C-C bond lengths differ somewhat. The calculated local mode frequencies are in good agreement with those observed. The formation of Cs-Cs has also been investigated. It is suggested that the center is formed when a vacancy is trapped by the metastable substitutional carbon-interstitial carbon center, Cs-Ci.
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| 5. |
- Nielsen, B. Bach, et al.
(författare)
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Local vibrational modes of weakly bound O-H complexes in SI
- 1997
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Ingår i: Defects in semiconductors. - : Trans Tech Publications Inc.. ; , s. 391-398
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Konferensbidrag (refereegranskat)abstract
- Local vibrational modes of two oxygen-hydrogen complexes have been identified with infrared absorption spectroscopy. Samples of intrinsic silicon and samples doped with 16O or 18O isotopes were implanted with protons and deuterons at ∼20 K. After the implantation, infrared absorbance spectra were measured at 8 K on unannealed samples. An oxygen mode at 1077 cm-1 and a hydrogen mode at 1879 cm-1, which originate from the same defect OHI were observed in the as-implanted samples. Heat-treatment at 200 K produced a new center OHII with modes at 1028 and 1830 cm-1. OHI anneals out at ∼130 K while OHII is stable up to ∼240 K. OHI and OHII are tentatively identified with two complexes of interstitial oxygen and bond-centred hydrogen. Ab initio theory was applied to calculate the structure and local modes of three such complexes. The results qualitatively support our tentative assignments.
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| 6. |
- Andersen, O., et al.
(författare)
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Electrical activity of carbon-hydrogen centers in Si
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:23, s. 235205-1
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Tidskriftsartikel (refereegranskat)abstract
- The electrical activity of Cs-H defects in Si has been investigated in a combined modeling and experimental study. High-resolution Laplace capacitance spectroscopy with the uniaxial stress technique has been used to measure the stress-energy tensor and the results are compared with theoretical modeling. At low temperatures, implanted H is trapped as a negative-U center with a donor level in the upper half of the gap. However, at higher temperatures, H migrates closer to the carbon impurity and the donor level falls, crossing the gap. At the same time, an acceptor level is introduced into the upper gap making the defect a positive-U center.
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| 7. |
- Andersen, O., et al.
(författare)
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Piezospectroscopic analysis of the hydrogen-carbon complexes in silicon
- 2001
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 139-142
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Tidskriftsartikel (refereegranskat)abstract
- We have observed the donor (Ec-0.22 eV) and acceptor (Ec-0.16 eV) levels related to hydrogen-carbon complexes in silicon. The donor level is only detected at low temperatures after proton implantation. This hydrogen-carbon complex irreversibly reconfigures at temperatures above 225 K to a configuration characterized by the acceptor level, which is stable up to room temperature. The same acceptor level is also observed after atomic hydrogen diffusion. We have used Laplace transform deep level transient spectroscopy (DLTS) to show the influence of uniaxial stress on the electron emission process and the effect of the stress-induced alignment for the acceptor state. The pattern of the Laplace DLTS peak splittings indicate a trigonal symmetry of the defect. First principles calculations were carried out on the hydrogen-carbon defects with a view of determining their electrical levels and stress response for comparison with the experimental results.
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| 8. |
- Filhol, J-S, et al.
(författare)
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Structure and electrical activity of rare-earth dopants in selected III-Vs
- 2003
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Ingår i: Materials Research Society Symposium Proceedings. ; , s. 471-476
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Konferensbidrag (refereegranskat)abstract
- Density functional theory is used to investigate Eu, Er and Tm rare earth (RE) impurities in GaAs, GaN and AlN. The most stable site is when the RE is located at a group III substitutional site but in GaN and GaAs these defects do not then possess any gap levels, unlike AlN. RE-V$_\mathrm{N}$ defects in GaN are shown to possess levels which could act as traps for excitons. The interaction of oxygen with substitutional REs is also considered.
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| 9. |
- Hourahine, B., et al.
(författare)
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Anomalous shift of the 1075 cm-1 oxygen-hydrogen defect in silicon
- 1997
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Ingår i: Defects in semiconductors, ICDS-19. - : Trans Tech Publications Inc.. ; , s. 277-282
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Konferensbidrag (refereegranskat)abstract
- First principles calculations are carried out on i) hydrogen and ii) water molecules trapped near an interstitial oxygen atom in Si. We find that it is possible for these molecules to cause an upward shift in the antisymmetric stretch mode of Oi when H is replaced by D, which could explain the anomalous shift in the 1075 cm-1 O-H related local vibrational mode. Both these molecules lead to modes in the 3500-4000 cm-1 region but those of the H2 lie close to those recently detected using Fourier transform infra-red spectroscopy.
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| 10. |
- Hourahine, B., et al.
(författare)
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Evidence for H2* trapped by carbon impurities in silicon
- 2001
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 197-201
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Tidskriftsartikel (refereegranskat)abstract
- Local mode spectroscopy and ab initio modelling are used to investigate two trigonal defects found in carbon-rich Si into which H had been in-diffused. Isotopic shifts with D and 13C are reported along with the effect of uniaxial stress. Ab initio modelling studies suggest that the two defects are two forms of the CH2* complex where one of the two hydrogen atoms lies at an anti-bonding site attached to C or Si, respectively. The two structures are nearly degenerate and possess vibrational modes in good agreement with those observed.
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