Interband Transitions in Ultrathin GaAs-AlAs Superlattices

Experimental as well as theoretical data for the optical properties of ultrathin GaAs-AlAs (001) superlattices are presented and analyzed. The dielectric functions ${\epsilon }_1\left(\omega \right)$ and ${\epsilon }_2\left(\omega \right)$ are calculated by means of the linear muffin-tin-orbital method, whereas the experimental data are obtained by means of ellipsometry. Theory and experiments agree with respect to the structures in ${\epsilon }_2$ and their variation in spectral position with superlattice period. Two structures specific to the superlattice are identified and explained in terms of the reduced symmetry as compared to the bulk materials. Variation of the polarization of the light is predicted to influence the optical properties only slightly.