| 1. |
- Blumenau, A.T., et al.
(författare)
-
Dislocations in hexagonal and cubic GaN
- 2000
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12, s. 10223-10233
-
Tidskriftsartikel (refereegranskat)abstract
- The structure and electronic activity of several types of dislocations in both hexagonal and cubic GaN are calculated using first-principles methods. Most of the stoichiometric dislocations investigated in hexagonal GaN do not induce deep acceptor states and thus cannot be responsible for the yellow luminescence. However, it is shown that electrically active point defects, in particular gallium vacancies and oxygen-related defect complexes, can be trapped at the stress field of the dislocations and may be responsible for this luminescence. For cubic GaN, we find the ideal stoichiometric 60° dislocation to be electrically active and the glide set to be more stable than the shuffle. The dissociation of the latter is considered
|
|
| 2. |
- Blumenau, A.T., et al.
(författare)
-
Straight and kinked 90° partial dislocations in diamond and 3C-SiC
- 2002
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:48, s. 12741-12747
-
Tidskriftsartikel (refereegranskat)abstract
- Density-functional based calculations are used to investigate low energy core structures of 90° partial dislocations in diamond and 3C-SiC. In both materials dislocation glide is analysed in terms of kink formation and migration and the fundamental steps to kink migration are investigated. We find the C terminated core structure in SiC to be more mobile than the Si core. However, the Si partial is electrically active and this opens the possibility of recombination-enhanced glide under ionizing conditions or an enhanced mobility in doped material.
|
|
| 3. |
- Coutinho, J., et al.
(författare)
-
Interstitial carbon-oxygen center and hydrogen related shallow thermal donors in Si
- 2002
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:1, s. 014109-11
-
Tidskriftsartikel (refereegranskat)abstract
- The interstitial carbon-oxygen defect is a prominent defect formed in e-irradiated Cz-Si containing carbon. Previous stress alignment investigations have shown that the oxygen atom weakly perturb the carbon interstitial but the lack of a high-frequency oxygen mode has been taken to imply that the oxygen atom is severely affected and becomes overcoordinated. Local vibrational mode spectroscopy and ab initio modeling are used to investigate the defect. We find new modes whose oxygen isotopic shifts give further evidence for oxygen overcoordination. Moreover, we find that the calculated stress-energy tensor and energy levels are in good agreement with experimental values. The complexes formed by adding both single (CiOiH) and a pair of H atoms (CiOiH2), as well as the addition of a second oxygen atom, are considered theoretically. It is shown that the first is bistable with a shallow donor and deep acceptor level, while the second is passive. The properties of CiOiH and CiO2iH are strikingly similar to the first two members of a family of shallow thermal donors that contain hydrogen.
|
|
| 4. |
- Coutinho, J., et al.
(författare)
-
Over-coordinated oxygen in the interstitial carbon-oxygen complex
- 2001
-
Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 305-308
-
Tidskriftsartikel (refereegranskat)abstract
- The interstitial carbon-oxygen complex is one of the most prominent defects formed in e-irradiated Cz-Si containing carbon. Stress alignment investigations have shown that the oxygen atom only perturbs the carbon interstitial but the lack of a high frequency oxygen mode has been taken to imply that the oxygen atom is over-coordinated. Local vibrational mode spectroscopy and ab initio modeling are used to investigate the defect. We find new modes whose oxygen isotopic shifts, along with the piezoscopic stress-energy tensor support the trivalent model, thus providing evidence for oxygen over-coordination.
|
|
| 5. |
- Coutinho, J., et al.
(författare)
-
Thermal double donors and quantum dots
- 2001
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 87:23, s. 235501-
-
Tidskriftsartikel (refereegranskat)abstract
- Combined local mode spectroscopy and ab initio modeling are used to demonstrate for the first time that oxygen atoms in thermal double donors (TDD) in Si are in close proximity. The observed vibrational modes in 16O, 18O, and mixed isotopic samples are consistent with a model involving [110] aligned oxygen chains made up of an insulating core lying between electrically active ends. The model also explains the minute spin density observed on oxygen in TDD+ as well as the piezospectroscopic tensors of the donors. The analogy between the thermal donors and quantum dots is emphasized.
|
|
| 6. |
- Goss, J.P., et al.
(författare)
-
First principles studies of H in diamond
- 2001
-
Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 186:2, s. 263-8
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio methods are used to investigate hydrogen defects in diamond. For the isolated impurity, the bond-centered site is found lowest in energy and posses both donor and acceptor levels. The neutral defect possesses a single local mode with very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H*2 defects which are also found to be almost IR-inactive. The complex between B and H is investigated and the activation energy for the reaction B-H → B - + H+ found to be in rasonable agreement with experiment. Hydrogen is strongly bound to dislocations which, together with H*2, may form part of the hydrogen accumulation layer detected in some plasma studies.
|
|
| 7. |
- Goss, J. P., et al.
(författare)
-
Theory of hydrogen in diamond
- 2002
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:11
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio cluster and supercell methods are used to investigate the local geometry and optical properties of hydrogen defects in diamond. For an isolated impurity, the bond-centered site is found to be lowest in energy, and to possess both donor and acceptor levels. The neutral defect possesses a single local mode with a very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H2* defects, which are also found to be almost IR inactive. The complex between B and H is investigated and the activation energy for the reaction B-H→B-+H+ found to be around 1.8 eV in agreement with experiment. We also investigate complexes of hydrogen with phosphorus and nitrogen. The binding energy of H with P is too low to lead to a significant codoping effect. A hydrogen-related vibrational mode of the N-H defect, and its isotopic shifts, are close to the commonly observed 3107-cm-1 line, and we tentatively assign this center to the defect. Hydrogen is strongly bound to dislocations which, together with H2*, may form part of the hydrogen accumulation layer detected in some plasma studies.
|
|
| 8. |
- Goss, J.P., et al.
(författare)
-
Vibrational modes and electronic properties of nitrogen defects in silicon
- 2003
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:4, s. 45206-1
-
Tidskriftsartikel (refereegranskat)abstract
- Nitrogen impurities form complexes with native defects such as vacancies and self-interstitials in silicon which are stable to high temperatures. These complexes can then suppress the formation of large vacancy and self-interstitial clusters. However, there is little known about their properties. We use first-principles density-functional theory to the determine the local vibrational modes, electrical levels and stability of a range of nitrogen-interstitial and vacancy complexes. Tentative assignments of the ABC photoluminescence line and the trigonal SL6 EPR center are made to substitutional-nitrogen pair and the substitutional-nitrogen-vacancy complex.
|
|
| 9. |
- Hourahine, B., et al.
(författare)
-
Evidence for H2* trapped by carbon impurities in silicon
- 2001
-
Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 197-201
-
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.
|
|
| 10. |
- Jones, R., et al.
(författare)
-
Structure and electronic properties of nitrogen defects in silicon
- 2004
-
Ingår i: Gettering and Defect Engineering in Semiconductor Technology GADEST 2003. - : Trans Tech Publications Inc.. ; , s. 93-98
-
Konferensbidrag (refereegranskat)abstract
- Nitrogen-vacancy defects in Si are of interest due to their ability to suppress the formation of large vacancy cluster during growth but there are problems in their characterisation. We use local density functional theory to determine the local vibrational modes, electrical levels and stability of a number of nitrogen defects. A prominent nitrogen local vibrational mode at 663 cm-1 is attributed to a nitrogen-vacancy centre and tentative assignments of the ABC photoluminescence line and the trigonal SL6 BPR centre are made.
|
|
