Interband transitions of thin-layer GaAs/AlAs superlattices

Spectroscopic ellipsometry has been used to study the confinement and interlayer coupling effects on the optical interband transitions of (GaAs${)}_m$(AlAs${)}_m$ superlattices. For superlattice periods d≥50 Å the confinement effect on the $E_1$ transition becomes negligible, whereas on the $E_0$ transition it is still appreciable. For thinner periods, a splitting of the $E_1$ transition, related to interlayer coupling, is observed. The results are compared with photoluminescence measurements. A linear muffin-tin-orbital calculation of the electronic structure of the m=1 superlattice enables us to assign the splitting of the $E_1$ transition to the appearance of two critical points in the Λ direction as a result of the strong interaction between the folded bands.