Tamm states in effective-mass superlattice with a defect

The electronic structure of perturbed effective-mass superlattices is discussed within the effective mass approximation. Expressions for bound state energies and wavefunctions in these structures are derived in general form, valid for any symmetric form of effective mass modulation. The special case of rectangular superlattices with a perturbation layer ("artificial" defect) is considered in more detail. The influence of the structure parameters on properties of Bragg-confined states is analysed. It is found that the fulfillment of Bragg conditions does necessarily lead to optimally localized Bragg-confined states in structures based on the effective mass modulation only. Peculiarities of bound states crossing the k/sub t/-induced zero energy gaps are also discussed.