| 1. |
- Lastras-Martínez, L. F., et al.
(författare)
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Reflectance difference spectroscopy of GaAs asymmetric surface quantum wells above the fundamental gap
- 1998
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 170:2, s. 317-321
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Tidskriftsartikel (refereegranskat)abstract
- We report Reflectance Difference (RD) measurement on (001) GaAs surface quantum wells (QW) under Ultra High Vacuum (UHV) conditions from 1.7 to 5.0eV. The QW is embedded between an arsenic-rich reconstructed GaAs surface and an AlAs barrier. The samples, grown by MBE with a protective arsenic cap layer, were heated to 320 and 430°C to desorb the As layer and form c(4 x 4) and (2 x 4) surface reconstructions, respectively. By modifying the surface reconstructure, we are able to separate the contributions to the optical anisotropy from the surface region (mainly associated with the As dimers) from those originating below the surface.
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| 2. |
- Rönnow, Daniel, et al.
(författare)
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Isotope effects on the electronic critical points of germanium : Ellipsometric investigation of the E1 and E1+ Delta(1) transitions
- 1998
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 5:1, s. 29-35
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Tidskriftsartikel (refereegranskat)abstract
- Within the past years the optical excitations of electrons have been measured for semiconductor samples of different isotope compositions. The isotope shift observed have been compared with calculations of the effects of electron-phonon interaction on the electronic band structure. While qualitative agreement has been obtained, some discrepancies remain especially concerning the E1 and E1 + Delta(1) transitions. We have remeasured the effect of isotope mass on the E1 and E1 + Delta(1) transitions of germanium with several isotopic compositions. The results, obtained by means of spectroscopic ellipsometry, confirm that the real part of the gap self-energies induced by electron-phonon interaction is larger than found from band structure calculations, while the imaginary part agrees with those calculations, which are based on a pseudopotential band structure and a bond charge model for the lattice dynamics. Our results agree with predictions based on the measured temperature dependence of the gaps. We compare our data for E1 and E1 + Delta(1) with results for the lowest direct (E0) and indirect (E9) gaps. The measured values of Δ0 and Δ1 increase noticeably with increasing isotope mass. Similar effects have been observed in the temperature dependence of Delta(1) in alpha-Sn and GaSb. A microscopic explanation for this effect is not available.
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