Optical properties of (311)-oriented GaAs/AlAs superlattices

The dielectric function for energies above the fundamental gap of (331)-oriented GaAs/AlAs superlattices has been investigated by ellipsometry and reflection difference spectroscopy. The superlattices have a monoclinic unit cell and are thus anisotropic in the plane of the superlattice layers. In addition, they can be grown with a periodic interface corrugation along the [2¯33] in-layer direction in the form of macrosteps with a height of 10.2 Å. The reduced symmetry leads to a splitting of the optical transitions, in particular of those in the energy range of the bulk GaAs ${\mathit{E}}_1$ and ${\mathit{E}}_1$+${\mathrm{\Delta }}_1$. The observed splittings are compared to tight-binding calculations of the dielectric function.