Low-energy electronic states in heterosrtuctures formed by ultranarrow layer (single or several monolayers thickness) are studied theoretically. The host material is described within the effective mass approximation and 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 ultranarrow layer, the transfer matrix is written 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 superlattice are determined by these parameters. Spectral dependency of absorption in superlattice due to photoexcitation of electrons from localized states into minibands is strongly dependent on the ultranarrow layers characteristics. Such a dependency can be used for verification of the transfer matrix parameters.
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