Direct and Indirect Excitons and Polaritons in Coupled Quantum Well Microcavities

We present an accurate calculation of exciton states in coupled quantum wells (CQWs) in an external electric field. The energies, oscillator strengths, and absorption spectrum of excitons in symmetric AlGaAs CQWs and asymmetric InGaAs CQWs are calculated for different electric fields. It is demonstrated that the ground state of the system switches from direct to indirect exciton with dramatic changes of its binding energy and oscillator strength, the calculated radiative lifetime being in quantitative agreement with a photoluminescence decay measurement in AlGaAs CQWs. At the same time, the brightest excited state represents a direct exciton which is almost unaffected by the external field. We have also applied the developed technique to the calculation of exciton-polariton states in CQW microcavities. In the strong coupling regime, the field dependent reflectivity shows a remarkable polariton anticrossing which is in good agreement with a recent experimental observation.