EXCITON RADIATIVE DECAY AND POLARITONS IN MULTIQUANTUM WELLS - QUANTUM-WELL-TO-SUPERLATTICE CROSSOVER

Radiative decay and energy shifts of an exciton in a multi-quantum well interacting with the vacuum electromagnetic field are studied. Superradiant decay is predicted for multi-quantum well stacks thinner than the optical wavelength lambda for the emitted photon, but also for considerably thicker stacks for states with excitation wavevectors near possible optical wavevectors. As the stack thickness exceeds lambda, long-lived polaritons associated with the emerging translational invariance in the vertical direction develop for most excitation wavevectors. Superlattice polariton dispersion is obtained and the effect of embedding the structure in an optical microcavity is discussed.