Electron spectrum and infrared transitions in semiconductor superlattices with a unit cell allowing for quasi-localised carrier states

We studied theoretically the electron spectrum and infrared transitions in a superlattice with a unit cell allowing for quasi-localised carrier states. The dispersion relation and the band structure of such a system have been found. We calculated the dipole matrix element for inter-subband carrier infrared transitions. The wave functions and the electron spectrum in this superlattice show a peculiarity when the energy of a band state approaches the energy of the quasi-localised state in the single cell. The absorption strength peaks up at the respective frequencies.