CALCULATED DEFECT STATES IN SEMICONDUCTOR SUPERLATTICES WITHIN A TIGHT-BINDING MODEL

The localized states which appear in a superlattice as a result of thickness variations of barriers or quantum wells are calculated in the framework of the tight-binding approximation. We obtain very simple formulas in terms of single-quantum-well parameters. There is always a localized state for an enlarged or narrowed quantum well. Two localized states exist in the case of decreased barrier thickness. The range of validity of the formulas is discussed as a function of the superlattice period.