Electron spectra in simple superlattices

Analysing electronic structure of crystal superlattices by the two-time retarded Green´s functions method, we got electron dispersion law. Besides continual energy zones of allowed electron states (as in the bulk), there appear forbidden energy zones as well as characteristic bottom and top energy gaps. By suitable choice of energy parameter of electron transfer between superlayers, one obtains that allowed energy zones spread outside the bulk energy limits. There arise the localized electron states. For some values of superlayers widths, energy minibands join in the center or at the end of first Brillouin zone.