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

Abstract

Using an ab initio, nonlocal pseudopotential method, we have calculated the reflectance anisotropy of three different models of the GaAs(001) (2\ifmmode\times\else\texttimes\fi{}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 \ensuremath{\sim}80% from that due to the \ensuremath{\beta}2(2\ifmmode\times\else\texttimes\fi{}4) model and \ensuremath{\sim}20% from that due to the \ensuremath{\alpha}(2\ifmmode\times\else\texttimes\fi{}4) model.