A theoretical investigation of the exciton formation process from free
carriers in a single GaAs/Al1-xGaxAs quantum well is presented. The m
echanism for the formation processes is provided by the interaction of
the electrons and holes with phonons. The contributions from both the
acoustic and optical phonons are considered. The relative importance
of exciton creation from a thermalized electron-hole gas (bimolecular
formation) versus a direct creation of excitons from the crystal groun
d state through the electromagnetic field (geminate formation) is disc
ussed. The formation process is analyzed for different densities and t
emperature of the free carriers, and for different intensities of the
exciting optical pump. The results compare reasonably well with recent
experiments.