Effect of Coulomb Interactions on the Density of States in Intentionally Disordered Superlattices

We study the effect of doping on the energy spectrum of a superlattice with intentional disorder related to fluctuations of the layer widths. Disorder-induced redistribution of carriers between the layers gives rise to Coulomb fields that shift the energy levels and produce a decrease in the width of the energy level distribution (vertical screening). We develop a nonlinear theory of vertical screening and show that the resulting level distribution can be strongly asymmetric with respect to the renormalized Fermi level, thus substantially reducing the total number of levels lying above it. This affects vertical hopping conduction, since these levels correspond to the "bottlenecks" of the effective resistance network.