Band-edge states in short-period (GaAs)m/(AlAs)nsuperlattices

We investigate the character of the electron and hole states in [001]-stacked (GaAs${)}_m$/(AlAs${)}_n$ superlattices with m,n≤3 by means of the first-principles linear–muffin-tin-orbital method. The highest valence states are found to localize more on the GaAs layers with increasing superlattice period, while the lowest conduction states at the Γ point are confined in the AlAs region in most cases. The calculated gaps (direct and indirect) compare well with experimental results. The heavy-hole- and light-hole-like states, split by the tetragonal perturbation of the superlattice, exhibit dispersions with strong nonparabolicities related to anticrossing of states for values of k close to the Γ point, and spin splittings along the superlattice layers. The effective masses of holes and electrons are calculated at the Γ point and are found to show little variation within themselves. The spin splittings are accounted for by k-linear terms. A semiempirical k⋅p perturbation theory is developed for the two highest valence states, the parameters of which are obtained by a fit to the first-principles bands.