Spectroscopic ellipsometry has been used to study the confinement and interlayer coupling effects of the optical interband transitions of (GaAs)m(AlAs)m superlattices. For superlattice periods d>or=50 AA 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 Lambda direction as a result of the strong interaction between the folded bands.
 

Physical Review B, 36 3254-8, 1987.