POLARITONS IN MULTIPLE-QUANTUM WELLS

A description of polariton effects on excitons in multiple quantum wells (MQWs), superlattices (SLs), and semiconductor microcavities is given, which is based on a nonlocal semiclassical theory in a transfer-matrix formulation. The radiative width in MQWs at k = 0 increases first with the number of wells N, then goes to zero as N --> infinity, where stationary polariton states are recovered. A very similar behavior is found by treating the MQW with a local dielectric model. In the SL limit, the exciton-polariton dispersion at long wavelengths reduces to that of a light wave in a uniaxial material, described by an effective dielectric tenser. Comparing with the bulk, the polariton splitting is increased in SLs, and reduced in microcavities. Nevertheless, polariton effects in microcavities are easily observable, since spatial coherence along the growth direction is not required.