In-plane spectrum in superlattices

We show that the existing theory does not give correct in-plane spectrum of superlattices at small in-plane momentum. Magnetoabsorption experiments demonstrate that the energy range of the parabolic region of the spectrum near the electron sub-band bottom is lower by an order of magnitude than the value predicted by the traditional approach. We developed a modified theory according to which the energy range of the parabolic region and carrier in-plane effective masses are determined by the effective band gap of the superlattice rather than by the bulk band gaps of the superlattice layers. The results of this theory are consistent with the experiment.