Impurity-band tails in superlattices

A calculation of the band tailing in heavily doped n-type superlattices is presented. We extend the semiclassical approach developed by Halperin and Lax for bulk materials and calculate the density of states in the low-energy tail for AlₓGa_1-xAs-GaAs superlattices. It is found that the density-of-states curve is shifted in energy in roughly the same way as the position of the lowest subband edge as the layer width is varied. The form of the band tailing is similar to bulk material if the superlattice is homogeneously doped.