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 A{} the confinement effect on the E₁ transition becomes negligible, whereas on the E₀ transition it is still appreciable. For thinner periods, a splitting of the E₁ 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 E₁ transition to the appearance of two critical points in the {Λ} direction as a result of the strong interaction between the folded bands.