Resonant impurity bands in semiconductor superlattices

It is shown that the 2pz confined impurity state of a semiconductor quantum well develops into an excited impurity band in the case of a superlattice. This is studied by following theoretically the transition from a single to a multiple quantum well or superlattice by exactly diagonalizing the three dimensional Hamiltonian for a quantum well system with random impurities. Intersubband
absorption experiments, which can be nearly perfectly reproduced by the theory, corroborate this interpretation, which also requires re-interpretation of previous data.