Quasiparticle Band Gaps for Ultrathin GaAs/AlAs(001) Superlattices.

The quasiparticle band energies for 1 x 1 and 2 x 2 GaAs/AlAs (001) superlattices have been calculated from first principles using a self energy approach. Both superlattices have indirect band gaps. The pseudodirect gaps at the zone center derived from folding of the Brillouin zone are larger than the direct gaps. The calculated results explain the various experimental data quantitatively. Matrix elements for optical transitions near the zone center show significant anisotropy. The effects of disorder on the observed spectra are discussed.