We studied the superlinearity of the photoluminescence intensity and its te
mperature dependence in GaAs/Ga1-xAlxAs heterojunctions by means of pump-pr
obe experiments. The photoluminescence intensity of the second laser pulse
increases drastically when the heterojunction is pre-excited by a short las
er pulse. We attribute this superlinearity to the vertical transport of the
photoexcited carriers driven by the interface electric field, and the subs
equent bimolecular exciton formation.