Reflectance Anisotropy of GaAs(100): Theory and Experiment

The reflectance anisotropy has been calculated by microscopic tight-binding theory for various configurations of the As-rich GaAs(100) $c(4\times 4)$ and $(2\times 4)$ reconstructions, based on precise atomic coordinates from ab initio total-energy minimization. The comparison to experimental reflectance anisotropy in combination with scanning tunneling microscopy and low energy electron diffraction allows one to identify precise correlations between structural units and optical features. Clear indications are obtained for the intermediate steps in the surface reconstruction transformation.