| 1. |
- Pritchard, R E, et al.
(författare)
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Bonding of H-CAs pairs in AlxGa1-xAs alloys
- 1994
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 50:15, s. 10628-10636
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Tidskriftsartikel (refereegranskat)abstract
- The local structure of CAs acceptors in AlxGa1-xAs has been investigated by studying the nondegenerate localized vibrational modes of H-CAs pairs with A1 symmetry, rather than those of isolated CAs impurities. Infrared absorption and Raman scattering measurements have been made on AlxGa1-xAs: 12C epilayers that (a) had been exposed to a radio-frequency hydrogen (deuterium) plasma or (b) contained hydrogen incorporated during growth. Arguments are advanced that indicate that the H(D) atom should occupy a bond-centered site between CAs and Ga atoms rather than between CAs and Al atoms at low temperatures. An ab initio local-density-functional calculation indicates that the energy is then lowered by 0.24 eV. This analysis has led to the assignment of five antisymmetric stretch modes and five symmetric (X) modes to H-CAs pairs at sites where the carbon atom that was originally unpaired had zero, one, two, three, or four Al nearest neighbors
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| 2. |
- Purton, J., et al.
(författare)
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LDF pseudopotential calculations of the α-quartz structure and hydrogarnet defect
- 1992
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Ingår i: Physics and chemistry of minerals. - 0342-1791 .- 1432-2021. ; 18:6, s. 389-392
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio LDF theory has been used to study the structure of the hydrogarnet defect in α-quartz. The predicted structure is in good agreement with the available sexperimental data. The techniques employed also yield a good model for the structure of α-quartz, giving an average Si-O bond length of 1.62 Å and average Si-O-Si angle of 142°.
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| 3. |
- Jones, R, et al.
(författare)
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Ab initio calculations of anharmonicity of the C-H stretch mode in HCN and GaAs
- 1994
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 50:12, s. 8378-8388
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Tidskriftsartikel (refereegranskat)abstract
- The anharmonicities of the C-H stretch modes in HCN and the passivated C acceptor in GaAs are investigated using ab initio local-density-functional cluster theory. The effective-mass parameter χ for the C-H stretch mode is shown to be less than unity in HCN, and greater than unity for the GaAs case. The calculated anharmonic parameter for the first defect is found to be 106 cm-1 and is in very good agreement with experiment. For the second defect, the anharmonicity is about 50% larger in agreement with empirical estimates. The frequencies of the fundamental transitions in both systems are shown to be very sensitive to the C-H length. This limits the accuracy of theoretical investigations of these high frequency H modes. Finally, the effects of electrical anharmonicity are considered and it is shown that they reduce the intensity of the overtone in the C-H complex in GaAs by about 70%.
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