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Reflectance anisotropy of the GaAs(001) (2 x 4) surface: Ab initio calculations.

Using an ab initio, nonlocal pseudopotential method, we have calculated the reflectance anisotropy of three different models of the GaAs(001) (2×4) surface. We find that the dominant contribution to the anisotropy comes from optical transitions between bulk valence-band states and unoccupied surface states. The best fit to the low-temperature experimental reflectance anisotropy spectrum, as observed in situ, is obtained from a linear combination of the calculated spectra from the different models taking ∼80% from that due to the β2(2×4) model and ∼20% from that due to the α(2×4) model