Stark ladders in periodically Si-δ-doped GaAs

We study theoretically the electronic structure of periodically Si delta-doped GaAs subject to a homogeneous electric field applied along the growth direction. The space-charge potential due to delta doping is obtained by means of the Thomas-Fermi approach. Analyzing the change in the density of states in the superlattice introduced in the electric field, we observe a set of equally-spaced sharp peaks corresponding to Stark-ladder resonances. Intrinsic broadening of resonances turns out to be smaller than the level spacing in the whole range of the electric field we consider. We use the inverse participation ratio to evaluate the spatial extent of electron wave functions, and we find that the Stark-ladder spectrum is related to a strong-localization regime at high field