Influence of hydrogen adsorption on the optical properties of the GaAs(100)-c(4×4) surface

We have investigated the influence of hydrogen adsorption on the optical anisotropy and the surface reconstruction of the GaAs(100)-c(4×{}4) surface using reflectance difference spectroscopy (RDS) and low-energy electron diffraction (LEED), respectively, At low exposures the optical anisotropy of the c(4×{}4) surface is removed almost completely by hydrogen adsorption due to removal of the As dimers in the outermost As layer, while the LEED pattern changes from c(4×{}4) to (1×{}1). At intermediate hydrogen exposures, the surface again becomes optically anisotropic showing the signature of Ga dimers in the RDS spectra, while LEED indicates a mixture of (1×{}2) and ({}2 ×{} {}2 ) reconstructions. Finally, at even higher dosages the Ga dimers are broken by hydrogenation. The LEED pattern shows a (1×{}1) symmetry and the RDS features are correlated with the critical points of the bulk electronic band structure.