Optical Transitions, Excitons, and Polaritons in Bulk and Low-Dimensional Semiconductor Structures

Abstract

Electrons in solids are subject to the crystal potential, as well as to the mutual electronelectron interaction. The resulting quantum-mechanical system represents a many-body problem of great complexity. In weakly-correlated systems like the usual semiconductors, a good starting point is provided by the one-particle picture, in which the crystal eigenstates are approximated by Slater determinants where the electrons occupy the one-particle eigenstates called band levels. This is only an approximate picture, since the electron-electron interaction yields corrections to the excited-state spectrum of the crystal. In particular, two-particle excitations called excitons arise at energies below the band gap, and excitonic corrections are found also at energies above the band gap.