Atomic structure and optical anisotropy of III-V(001) surfaces

The optical anisotropy of materials with isotropic bulk crystal structure d epends to a large extent on the surface atomic structure. For instance, dat a obtained by reflectance anisotropy spectroscopy (RAS) on (001) surfaces o f zinc blende semiconductors such as InP and GaAs, have a fingerprint chara cter for the various surface reconstructions. Here we present RAS spectra f or GaAs(001) and InP(001) recorded at room temperature and at low temperatu re. We show that by comparison with a theoretical analysis based on ab init io density functional theory in local-density approximation calculations th e origin of characteristic spectral features can be identified and thus RAS spectra utilized to discriminate between different competing structural mo dels. We identify contributions related to electronic transitions between s urface states as well as features arising from surface perturbed bulk wave functions. We explain the high sensitivity of RAS to the surface structure. and chemistry as due to the surface state related features. (C) 2001 Ameri can Vacuum Society.