Ordering of conduction band states in (GaAs)_n(AlAs)_n[001] and [110] superlattices

The local empirical pseudopotential theory, implemented via the S-matrix layer method has been used to study the conduction band state ordering in (GaAs)n(AlAs)n superlattices grown in the [001] and [110] directions. An oscillatory dependence of the energies on the layer thickness n is found. It is shown that the Gamma -state becomes the lowest energy state for n>or=8 in the [001] case, and for n>or=12 in the [110] case.