In the realistic EuS/PbS/EuS quantum well system with strong material parameter contrasts in heteroboundaries (MPCH) a collective plasmon-phonon excitation spectrum for a weakly polar quasi-two-dimensional electron gas interacting with the longitudinal optical phonons is investigated. The calculations are carried out within the framework of the random-phase approximation by use of exactly calculated dielectric function of an electron gas. The analytical and numerical deviations from the results when MPCH is absent are established. The mode coupling due to MPCH for typical moderate low in-plane densities ( 3.5.1011 cm-2 ) is presented. It is shown, that in this realistic structure a low plasmon-like coupled mode is deeply suppressed and high phonon-like mode weakly depends from the transverse optical frequency due to the lead salt material features.
The spatial and time dependencies of the dielectric function for the quasi-two dimensional (Q2D) electron gas (EG) in
a finite confining potential quantum well (QW) are calculated by using a self-consistent approach (SQF). Taking into
account the influences of mismatch of strong discontinuous dielectric constant and effective masse across the interfaces
the dielectric response function analytic expressions are derived for a rectangular finite potential barrier QW for the first
time. The deviations from the results when these mismatches are absent are established. By using exactly calculated
dielectric function a comparison with the respective asymptotic expressions of finite and infinite confining models is
presented both analytically and numerically on the base of realistic EuS/PbS/EuS QW. The transition interval between
2D and 3D cases has been demonstrated numerically.