Concept of local polaritons and optical properties of mixed crystals and quantum heterostructures.

摘要

This thesis is devoted to a study of local polariton modes that appear inside the polariton bandgap of polar dielectrics and semiconductors due to microscopic defects in a crystal lattice. We show that these modes strongly affect the optical properties of the material and lead to new effects, such as resonance electromagnetic wave tunneling.; Using analytical calculations complemented with numerical simulations in one and three dimensions, we find that at high concentrations of the impurities, local polariton modes develop into an impurity induced band inside the original polariton bandgap. We derive the dielectric function of the impure crystal for an arbitrary concentration of the defects and put forward an explanation of numerous experiments on the far-infrared optical properties of mixed polar crystals.; We propose a mechanism to make local polariton modes tunable. It is based on the fact that electron transitions involving deep centers in semiconductors may lead to reversible changes in the frequency of the existing local polaritons. For a large concentration of the defects, the alteration of the local elastic constants can lead to the creation of the polariton band or to a shift of the existing band (and/or to alteration of its shape). We also review materials where these effects may be observed experimentally.; The formalism developed for a one-dimensional model of discrete non-interacting point-like dipoles coupled to the retarded electromagnetic field is shown to describe normal propagation of light through a system of multiple quantum wells with different types of structural defects. Local polariton states can be excited by an evanescent electromagnetic mode at normal incidence, and may cause the resonant transmission. We study how imperfections in a periodic multiple quantum well structure can be used to control its optical spectra, which presents significant experimental interest.