Exciton-polaritons in quantum wells

Abstract

An overview of the properties of excitons in quantum wells is presented, together with a discussion of polariton effects. Exciton binding energies are calculated including valence band mixing, Coulomb coupling between different subbands, nonparabolicity, and the dielectric mismatch: all these effects are found to be of a comparable size. Theoretical results agree within a few tenths of a meV with photoluminescence excitation experiments. Valance band mixing gives a finite oscillator strength to some excitons not in s-states, but does not change the selection rules based on parity. Inclusion of the interaction with radiation gives rise to polariton states, which, however, are surface modes and are not observed in usual optical experiments. Free quantum-well excitons are shown to have a finite radiative lifetime, unlike in bulk crystals, due to the lack of translational invariance along the growth direction. Due to thermalization processes, the radiative decay width must be averaged over the thermal distribution, resulting in an effective radiative lifetime which rises linearly with temperature. This behavior, as well as the calculated lifetimes, is in qualitative agreement with experiment.