Abstract

A blue shift of the exciton line has been recently observed¹ in MQWS (53 Å GaAs-53 Å GaAlAs) after femtosecond excitation. This shift has been proved to originate from the presence of large number of excitons in the system, either directly created by resonant pumping or due at longer delay to the pairing of the electrons and holes initially created by band to band excitation at low temperature. This blue shift has not been reported in the bulk material GaAs. This effect being related to the sample structure, it is important to know whether the two-dimensional confinement within a well is the only origin of this new type of exciton interaction or if the superlattice type of the sample has to play a role. Experiments have been performed in MQWS with different barrier and well thicknesses, ranging from the case of thick barriers (in order to minimize the interactions between the wells) to the case where excitonic wave functions overlap over neighboring wells. The experimental results demonstrate the influence of the superlattice structure- A model is developped which takes into account the difference between the bulk material isolated wells and superlattices.

© 1985 Optical Society of America