Electronic states in heterostructures formed by ultranarrow layers.

Low-energy electronic states in heterostructures formed by ultranarrow layers (single or several monolayers in thickness) are studied theoretically. The host material is described within the effective mass approximation and the effect of ultranarrow layers is taken into account within the framework of the transfer matrix approach. Using the current conservation requirement and the inversion symmetry of an ultranarrow layer, the transfer matrix is evaluated through two phenomenological parameters. The binding energy of localized state, the reflection (transmission) coefficient for the single ultranarrow layer case, and the energy spectrum of the superlattice are determined by these parameters. The spectral dependency of absorption due to photoexcitation of electrons from localized states into minibands of the superlattice is determined by the ultranarrow layer characteristics. Such a dependency can be used for verification of the transfer matrix and should modify the characteristics of optoelectronic devices with ultranarrow layers. Comparison with experimental data shows that the effective mass approach is not valid for the description of ultranarrow layers.