| 21. |
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| 22. |
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| 23. |
- Persson, Clas, et al.
(författare)
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Optical and reduced band gap in n- and p-type GaN and AlN
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:6, s. 3207-3216
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Tidskriftsartikel (refereegranskat)abstract
- We present a full band calculation of the doping-induced energy shifts of the conduction-band minimum and the valence-band maximum for n- and p-type GaN and AlN. Both wurtzite and zinc-blende structures have been considered. The resulting optical and reduced band-gap energies are presented as functions of the ionized impurity concentration in the heavily doped regime. The computational method is based on a zero-temperature Green's function formalism within the random phase approximation and with the local-field correction of Hubbard. The calculation goes beyond the spherical approximation of the energy bands by using energy dispersions and overlap integrals from a first-principle, full-potential band-structure calculation. Inclusion of the spin-orbit interaction is crucial for describing the uppermost valence bands properly, and we show that the nonparabolicity of the valence bands influences the energy shifts strongly, especially the shift of the optical band gap. With the full band structure, we can explain the results of photoluminescence measurements by Yoshikawa [J. Appl. Phys. 86, 4400 (1999)].
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| 24. |
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| 25. |
- Qian, M. C., et al.
(författare)
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Atomic and electronic properties of anion vacancies on the (110) surfaces of InP, InAs, and InSb
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:15
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Tidskriftsartikel (refereegranskat)abstract
- We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and the electronic structure of the anion vacancy on the (110) surfaces of InP, InAs, and InSb. An inward relaxation of the three neighboring In atoms next to the anion vacancy is obtained, but the stable atomic structure depends critically on the vacancy charge state. The +1 charged vacancy exhibits a nonsymmetric configuration with one rebonded dimer, while both 0 and -1 charged vacancies show a symmetric configuration with loosely rebonded and rebonded trimer, respectively. For InP and InAs, the charge-transfer levels epsilon(+1/0) and epsilon(0/-1) are located around the center of the band gap; whereas for InSb, the -1 charge state is stable in the whole band gap. In contrast to bulk, the surface vacancy is a positive-U center. The band structures and the density of states have been calculated. Three vacancy states, one deep in the valence band and two around the band gap, are identified. Our results show that the character of the vacancy states is mainly dependent on the atomic configuration.
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Smirnova, E. A., et al.
(författare)
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Effect of band filling on the pressure-induced structural transition in Mo-Re alloys
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:2
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Tidskriftsartikel (refereegranskat)abstract
- We report on a detailed investigation of the combined effect of alloying and compression on the structural stability of random bcc and hcp alloys in the Mo-Re system. We use the linear-muffin-tin-orbital Green's-function method within the coherent potential approximation (LMTO-GF-CPA) and the full-potential linear-muffin-tin-orbital (FP-LMTO) method. For pure Mo we find a bcc to hcp transition pressure to take place at 620 GPa (FP-LMTO) or 730 GPa Mbar (LMTO-GF-CPA). The calculated equation of states for Mo68Re32 alloy is in good agreement with the experimental data, and the calculated bcc-hcp transition pressure is above 400 GPa. This number is much higher than the one anticipated in earlier model calculations. The agreement between the model calculations, ab initio calculations, and the experiment is restored when self-consistent occupation numbers of sp and d electrons are used.
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| 30. |
- Smirnova, E. A., et al.
(författare)
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Electronic topological transitions and phase stability in the fcc Al-Zn alloys
- 2002
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 30:1, s. 57-66
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Tidskriftsartikel (refereegranskat)abstract
- We report on a detailed investigation of the phase equilibria and the Fermi surface in the Al-Zn system. Our calculation are based on the density functional theory and we use the linear muffin-tin orbital method and the Green's function technique. The calculated free energies of alloy formation exhibit the existence of a miscibility gap between the alloys containing approximately 10 and 55 at.% of Zn, in agreement with the phase diagram of the Al-Zn system. Seven electronic topological transitions (ETT) were found in Al-Zn system within the stability range of the fcc solid solution. A relation between these ETT and the phase stability of the fcc Al-Zn solid solutions is established. We show that extremum points on the concentration dependencies of the thermodynamic properties of Al-Zn alloys can be explained by band-filling effects.
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