  Dynamics of nonradiative excitons with large in-plane wave vectors forming a
so-called reservoir is experimentally studied in a high-quality semiconductor
structure containing a 14-nm shallow GaAs/Al$_{0.03}$Ga$_{0.97}$As quantum well
by means of the non-degenerate pump-probe spectroscopy. The exciton dynamics is
visualized via the dynamic broadening of the heavy-hole and light-hole exciton
resonances caused by the exciton-exciton scattering. Under the non-resonant
excitation free carriers are optically generated. In this regime the exciton
dynamics is strongly affected by the exciton-carrier scattering. In particular,
if the carriers of one sign are prevailing, they efficiently deplete the
reservoir of the nonradiative excitons inducing their scattering into the light
cone. A simple model of the exciton dynamics is developed, which considers the
energy relaxation of photocreated electrons and holes, their coupling into
excitons, and exciton scattering into the light cone. The model well reproduces
the exciton dynamics observed experimentally both at the resonant and
nonresonant excitation. Moreover, it correctly describes the profiles of the
photoluminescence pulses studied experimentally. The efficient exciton-electron
interaction is further experimentally verified by the control of the exciton
density in the reservoir when an additional excitation creates electrons
depleting the reservoir.
