Electron-phonon interaction in zinc oxide. Plasmon-optical phonon coupled modes

The effects of the electron-phonon interaction in zinc oxide depending on the free conduction band electron concentration are invetigated. In n-doped polar semiconductors, as the free carrier concentration is increased, the plasmonic mode associated to charge density fluctuations gradually approaches, its frequently to the optical phonon ones. As a consequences, their interaction is materialized in coupled mode oscillations. Using a dielectric cotinuum-model, applying the equation of motion technique for the operator associated to charge density fluctuations in ZnO, and taking in to account the supplementary constraints introduced by its uniaxial symmetry, the response function of the system is obtained. In polar semiconductors with cubic crystalline structure there are two plasmons-optical phonon coupled modes. It is shown that in ZnO, three such coupled modes appear. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim