SEMICONDUCTOR SUPERLATTICES WITH SMALL BAND OFFSETS

Optical transitions in small band offset superlattices are studied wit hin the framework of the nearly free electron approximation, in which the weak superlattice potential is treated as a perturbation. Interban d selection rules are derived for transitions involving conduction and valence band states at the superlattice Brillouin zone center and the zone edge. It is found that a number of new transitions can occur in such small-offset superlattices due to wave function mixing of differe nt subband states. The effect of the effective mass on the optical tra nsitions is also discussed. The theory is used to explain the results observed in magneto-optical absorption experiment in ZnSe/Zn1-xMnxSe s mall-offset superlattices. Furthermore, the nearly free electron formu lation is found to be in excellent agreement with rigorous multi-band numerical calculation on superlattices involving small band offsets.