Photoluminescence from two dimensional electrons at single heterojunctions

We have investigated photoluminescence from GaAs Al_xGa_1-xAs single heterojunctions. Along with the bulk AlGaAs and GaAs luminescence, the spectra have a component which arises from recombination of two dimensional electrons with holes trapped at or near the interface. Using ultra-violet excitation, the luminescence from the electrons at the interface is greatly enhanced relative to the GaAs bulk recombination. A positive front gate bias shifts the signals from the interface to higher energies, as expected. We observe several peaks and shoulders in the spectra which appear to correspond to different electron subbands.