  We report on the measurements of the kinetics of expanding and collapsing
rings in the exciton emission pattern. The rings are found to preserve their
integrity during expansion and collapse, indicating that the observed kinetics
is controlled by charge carrier transport rather than by a much faster process
of exciton production and decay. The relation between ring kinetics and carrier
transport, revealed by our experiment and confirmed by comparison with a
theoretical model, is used to determine electron and hole transport
characteristics in a contactless fashion.
