Theory of collective excitations in semiconductor superlattice structures

In this paper electronic collective excitations of type-I and -II superlattices are examined in detail. Type-I superlattices consist of quasi-two-dimensional layers of electrons, while type-II superlattices consist of alternating quasi-two-dimensional layers of electrons and holes. We use a simple model of the electronic structure and linear-response theory to calculate the density response of the system to an external perturbation. From this, we obtain an expression for the dielectric tensor, the zeros of which yield the dispersion relations of the collective modes. The theory is such that one can take into account many-body effects (depolarization and excitonic shifts), magnetic fields, and electron-phonon coupling in a simple way. A rich spectrum of excitations is found: quasi-two-dimensional plasmons, intersubband plasmons, magnetoplasmons, phonon-plasmon modes, and so on. Some interesting features of the excitations are examined, and their relevance to experiment is discussed.