Theory of exciton-polaritonic absorption in multiple quantum wells

A theory is presented for electromagnetic energy transfer and absorption mediated by quasi-two-dimensional excitons in regular multiple-quantum-well (MQW) structures. The absorptivity, absorption coefficient and their integrals over the photon frequency are generally expressed as functions of the ratio between the excitonic non-radiative and radiative damping rates. The dependences of the integral absorption characteristics on the non-radiative damping rate Gamma of an exciton are found to decrease at small Gamma, so do at low temperatures the dependences on temperature due to phonon-assisted decay of the exciton. Such behaviour of integral absorption versus the non-radiative damping rate is ascribed to the specific role of radiative exciton decay to be accompanied by photon escape from a finite-length MQW structure. That manifests itself as a violation of the Bouguer law at weak non-radiative damping or low temperatures.