The complete spectrum of eigenwaves including surface plasmon polaritons
(SPP), dynamic (bulk) and complex waves in the layered structures containing
semiconductor and metallic films has been explored. The effects of loss,
geometry and the parameters of dielectric layers on the eigenmode spectrum
and, particularly, on the SPP modes have been analysed using both the
asymptotic and rigorous numerical solutions of the full-wave dispersion
equation. The field and Poynting vector distributions have been examined to
identify the modes and elucidate their properties. It has been shown that
losses and dispersion of permittivity qualitatively alter the spectral
content and the eigenwave properties. The SPP counter-directional power
fluxes in the film and surrounding dielectrics have been attributed to
vortices of power flow, which are responsible for the distinctive features
of SPP modes. It has been demonstrated for the first time that the maximal
attainable slow-wave factor of the SPP modes guided by thin Au films at
optical frequencies is capped not by losses but the frequency dispersion of the actual Au permittivity.