| 1. |
- Elsner, J., et al.
(författare)
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Deep acceptors trapped at threading-edge dislocations in GaN
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 58:19, s. 12571-12574
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Tidskriftsartikel (refereegranskat)abstract
- Local-density-functional methods are used to examine the behavior of the oxygen defect, gallium vacancy, and related defect complexes trapped at threading-edge dislocations in GaN. These defects are found to be particularly stable at the core of the dislocation where oxygen sits twofold coordinated in a bridge position. VGa-ON is found to be a deep double acceptor, VGa-(ON)2 is a deep single acceptor, and VGa-(ON)3 at the dislocation core is electrically inactive. We suggest that the first two defects are responsible for a deep acceptor level associated with the midgap yellow luminescence band.
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| 2. |
- Elsner, J., et al.
(författare)
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Effect of oxygen on the growth of (101‾0) GaN surfaces : The formation of nanopipes
- 1998
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 73:24, s. 3530-3532
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Tidskriftsartikel (refereegranskat)abstract
- Local density-functional methods are used to examine the behavior of O and O-related defect complexes on the walls of nanopipes in GaN. We find that O has a tendency to segregate to the (10 1̄ 0) surface and identify the gallium vacancy surrounded by three oxygen impurities [VGa-(ON)3] to be a particularly stable and electrically inert complex. We suggest that during Stranski-Krastanow growth, when interisland spaces shrink, these defects reach a critical concentration beyond which further growth is prevented and nanopipes are formed
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| 3. |
- Elsner, J., et al.
(författare)
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Structural and electrical properties of threading dislocations in GaN
- 1997
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Ingår i: Defects in semiconductors. - : Trans Tech Publications Inc.. ; , s. 1203-1210
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Konferensbidrag (refereegranskat)abstract
- The atomic structures and electrical properties for threading screw and threading edge dislocations of wurtzite GaN are calculated within the local-density approximation. Both dislocations are electrically inactive with a band gap free from deep levels. These results are understood to arise from relaxed core structures which are similar to (1010) surfaces. The threading screw dislocations are found to be stable with an open-core whereas the threading edge dislocations possess filled cores.
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| 4. |
- Elsner, J, et al.
(författare)
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Theory of threading edge and screw dislocations in GaN
- 1997
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 79:19, s. 3672-3675
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Tidskriftsartikel (refereegranskat)abstract
- The atomic structures, electrical properties, and line energies for threading screw and threading edge dislocations of wurtzite GaN are calculated within the local-density approximation. Both dislocations are electrically inactive with a band gap free from deep levels. These results are understood to arise from relaxed core structures which are similar to (101̅ 0) surfaces.
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| 5. |
- Gutiérrez, R., et al.
(författare)
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The formation of nanopipes caused by donor impurities in GaN: A theoretical study for the case of oxygen
- 1999
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 79:3, s. 147-152
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Tidskriftsartikel (refereegranskat)abstract
- Local density-functional methods are used to examine the behaviour of O and O-related defect complexes at {1010}-type surfaces in GaN. We find that O has a tendency to segregate to the (1010) surface and we identify the gallium vacancy surrounded by three oxygen impurities (VGa-(ON)3) to be a particularly stable and electrically inert complex. We suggest that these complexes impede growth at the walls of the nanopipes preventing them from growing in. Also, other donor-related defect complexes, in particular gallium vacancies surrounded by three silicon atoms as second nearest neighbours, are expected to have the same effect.
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| 6. |
- Jones, R, et al.
(författare)
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Interaction of oxygen with threading dislocations in GaN
- 1999
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 171:1, s. 167-173
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Tidskriftsartikel (refereegranskat)abstract
- A review is given of the results of first principles calculations used to investigate the structures and electronic properties of screw and edge dislocations in GaN. The atoms at the core of the full core screw dislocation possess heavily strained bonds leading to deep gap states. Removing the first shell of Ga and N atoms gives a screw dislocation with a small open core consisting of {101-0} type surfaces. Therefore open-core screw dislocations induce only shallow gap states. In the same way we found the core of the threading edge dislocation to be reconstructed without any deep states. The interaction of oxygen with the cores of open-core screw and edge dislocations is considered and it is found that the impurity has a strong tendency to be bound by Ga vacancies leading to three types of defect trapped in the strain field. We suggest that the most stable defect leads to a poisoning of growth centres on the walls of nanopipes.
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| 7. |
- Markevich, V.P., et al.
(författare)
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Local vibrational mode bands of V-O-H complexes in silicon
- 1999
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 300-304
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Tidskriftsartikel (refereegranskat)abstract
- H2 molecules, which are introduced into moderately doped silicon crystals by high-temperature in-diffusion from H2 gas ambient followed by fast cooling to room temperature, are found to interact effectively with the defects induced by irradiation of the crystals with fast electrons. In Czochralski-grown silicon crystals, the interaction of the mobile H2 molecules with vacancy-oxygen defects (A centers) leads to the creation of V-O-H2 complexes. This complex gives rise to infrared (IR) absorption lines at 943.5, 2126.4, and 2151.5 cm-1. Ab initio calculations showed that the most stable configuration of V-O-H2 consists of one oxygen and two hydrogen atoms sharing a vacancy site. It is suggested that the interaction of the V-O-H2 complexes with interstitial oxygen atoms results in the formation of V-O2-H2 complexes, which are responsible for the IR absorption line at 891.5 cm-1.
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| 8. |
- Sitch, P.K., et al.
(författare)
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An ab initio study of the 90° partial dislocation core in diamond
- 1997
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Ingår i: Journal de Physique III. - : EDP Sciences. - 1155-4320 .- 1286-4897. ; 7:7, s. 1381-1387
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Tidskriftsartikel (refereegranskat)abstract
- The electronic and structural properties of the 90° glide partial dislocation in diamond are investigated using an ab initio local density functional cluster method. The core C-C bond is found to be reconstructed with a bond length 5% longer than that in bulk diamond. The formation and migration energy of the kink on the dislocation are calculated to be 0.32 and 2.97 eV respectively. Further, the shift of the gap levels during kink motion suggests that p-type doping will lead to an increase in the mobility of the partial.
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| 9. |
- Stich, P. K., et al.
(författare)
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Ab initio investigation of the dislocation structure and activation energy for dislocation motion in silicon carbide
- 1995
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 52:7, s. 4951-4955
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Tidskriftsartikel (refereegranskat)abstract
- The structures of straight 90° glide partial dislocations in SiC are calculated using an ab initio local density functional cluster method. Si partials containing core Si atoms are found to be strongly reconstructed with a Si-Si bond of comparable length to that in bulk silicon. The C partial possessing core C atoms is more weakly reconstructed with a bond length 16% longer than that in bulk diamond. The formation and migration energies of kinks on the partials are calculated and indicate that the C partial is the more mobile. The calculations also predict that n-type doping leads to an increase in the mobility of C partials whereas p-type doping increases the mobility of Si partials.
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| 10. |
- Öberg, Sven, et al.
(författare)
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First-principles calculations of the energy barrier to dislocation motion in Si and GaAs
- 1995
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 51:19, s. 13138-13145
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Tidskriftsartikel (refereegranskat)abstract
- The single kink formation and migration energies Fk and Wm of 90° glide partial dislocations in Si and GaAs are calculated using an ab initio local density-functional cluster method. Kink migration occurs via a concerted exchange of an atom at a dislocation core with one of its glide plane nearest neighbors. By constraining these atoms to sit in high-energy positions and relaxing a surrounding cluster of atoms, sufficient points in configuration space can be sampled for the energy barrier for the first step in kink pair formation to be estimated. By including an estimate of the elastic energy of the interaction of kink pairs, the single kink formation energy is calculated. It is found that Fk and Wm for Si are 0.1 and 1.8 eV, respectively. For the 90° α glide partial in GaAs, these quantities are 0.07 and 0.7 eV, respectively, and 0.3 and 1.1 eV for β partials
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