Reflectance anisotropy of GaAs(100): Dislocation-induced piezo-optic effects

We develop a model to describe reflectance-difference (RD) spectra of zinc-blende semiconductors due to strains induced by alpha and beta 60 degrees dislocations. It is shown that near the semiconductor surface, as a result of the lost of lattice periodicity, dislocations result in an anisotropic average strain that changes the symmetry from cubic to orthorhombic, thus leading to a reflectance anisotropy. We obtain expressions for RD spectra at critical points of both Gamma and Delta symmetry that predict first-derivative RD line shapes as long as the strain-induced energy shifts are small compared to spectra broadening energies. Furthermore, we report on RD spectra of semi-insulating GaAs (100) in the 1.2-5.5-eV energy range and show that such spectra comprise a component that is well described by our model.