EXCITON-EXCITON COLLISIONS AND CONVERSION OF INTERWELL EXCITONS IN GAAS ALGAAS SUPERLATTICES/

The ratio of the densities of intra- and interwell excitons in a symme tric system of coupled quantum wells - a superlattice based on a GaAs/ AlGaAs heterostructure - is investigated over a wide range of optical excitation power densities. Conversion of interwell excitons into intr awell excitons as a result of exciton-exciton collisions is observed a t high exciton densities. Direct evidence for such a conversion mechan ism is the square-root dependence of the interwell exciton density an the optical excitation level, The decrease in the lifetime of interwel l excitons with increasing excitation density, as measured directly by time-resolved spectroscopy methods, confirms the explanation proposed for the effect. (C) 1997 American Institute of Physics.