Selectively excited room-temperature photoluminescence spectra of InGa
As-GaAs-AlGaAs quantum well heterostructures reveal a broad line at mi
dgap energies originating in the Si doped AlGaAs. When carriers are ph
otoexcited directly in the wells, this line is dramatically enhanced a
t the expense of the quantum well line, indicating carriers escape fro
m the wells. The broad emission and its enhancement can be explained i
n terms of recombination between electrons trapped at DX centers in Al
GaAs and holes transferred into AlGaAs from the neighboring wells. We
also observe the broad emission by direct over-the-gap photoexcitation
of very highly doped Si:AlGaAs. The doping dependence consistently co
rrelates this line to DX centers.