Interplay of surface reconstruction and surface electric fields in the optical anisotropy of GaAs(001)

Abstract

The optical anisotropy of $c(4\ifmmode\times\else\texttimes\fi{}4),$ $(2\ifmmode\times\else\texttimes\fi{}4),$ $(2\ifmmode\times\else\texttimes\fi{}6)$ and $(4\ifmmode\times\else\texttimes\fi{}2)$ reconstructed GaAs(001) surfaces has been calculated from first principles. It consists of surface structure-dependent features originating from electronic transitions in the uppermost surface layers and of anisotropy peaks close to the ${E}_{1}$ and ${E}_{0}^{\ensuremath{'}}{/E}_{2}$ bulk critical point energies. The latter contributions are nearly structure independent and arise from transitions between surface-modified bulk electronic states. For the smaller reconstructions the influence of surface electric fields on the optical anisotropy is studied. We find that the linear electro-optic effect modifies mainly the optical anisotropy from the bulk atomic layers, resulting in changes of the reflectance anistropy spectroscopy signal which are strongly reconstruction dependent, however. Changes of the atomic relaxation due to surface electric fields are less important for the modification of the optical signal than the polarization of the electron wave functions.