Photoluminescence from the two-dimensional electron gas at GaAs/AlGaAs single heterojunctions

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Abstract
We have studied photoluminescence from GaAs/Al0.3Ga0.7 As modulation‐doped single heterojunctions, using excitation sources from infrared to ultraviolet near‐liquid‐helium temperature. The spectra have a strong interface component, accompanied by bulk GaAs and AlGaAs band‐gap luminescence. Using ultraviolet instead of infrared as the excitation, the interface signal is greatly enhanced relative to the bulk GaAs luminescence. The interface signal can be shifted to the higher energies when a semitransparent front gate is positively biased. Our observations indicate that the interface luminescence comes from the recombination of the two‐dimensional electrons with holes trapped at or near the interface. The peaks and the shoulders in the interface spectra appear to correspond to subbands of the two‐dimensional electron gas at the interface. Our results demonstrate the feasibility of doing spectroscopic studies on high‐mobility electrons at single heterojunctions.