The role of surface phonons in the formation of the spectrum of polaron states in quantum dots

The theory of large-radius polarons in quantum dots is developed with the difference in dielectric properties between the materials of the quantum dot and surrounding matrix taken into consideration. It is shown that the magnitude of the polaron effect is essentially dependent on the spectrum of surface optical phonons. The polaron shift of the size-quantized energy levels for electrons and holes is determined taking into account their interaction with phonons in the bulk and surface phonons. The conditions in which the interaction with surface phonons prevails are defined. It is shown that, in the II-VI compounds, the energy of the interaction can be higher than 10 meV and, hence, should be taken into account in calculating the energy spectrum. An approximate method for treating the polaron states is developed. The method provides a means for determining the magnitudes of the polaron shift in differently arranged heterostructures. It is found that the results obtained for the effect of surface phonons on the polaron states by the approximate method and by exact calculations are in good agreement