We study a model of a finite semiconductor superlattice with the last quantum well embedded in contact with an internal potential barrier of arbitrary height. By solving recurrence relations in the envelope-function approximation, we have obtained an explicit equation giving the energy levels of the electronic states. In the infinite limit, it is shown that ‘‘Tamm’’ surface states are possible below (or above) critical curves. The Tamm-state energies are computed as a function of the last well width W. Finally, for a finite typical superlattice, the energies of all the electronic modes are shown as a function of the width W.

• Received 1 December 1992

DOI:https://doi.org/10.1103/PhysRevB.48.7930