GaAs(001): Surface structure and optical properties

The optical anisotropy of differently reconstructed GaAs(001) surfaces has been analysed both theoretically and experimentally. The atomic structures and RAS spectra are calculated from first principles for the As-rich c(4 x 4) and beta2(2 x 4) as well as for the stoichiometric alpha2(2x4) and the Ga-rich zeta(4 x 2) surface phases. These results are compared with spectra recorded at low temperature (40 K). We find good agreement between the calculated and measured data, in particular for the As-rich surface phases. In marked contrast to earlier calculations we find the peak near the E-1 critical point energy, characteristic of the beta2(2 x 4) surface, to originate from electronic transitions in bulk layers. The experimental data for the Ga-rich (4 x 2) surface phase are less well reproduced, possibly due to surface defects or structural deviations from the zeta(4 x 2) model for the surface geometry.