Observation of luminescence from the 2s heavy-hole exciton in GaAs-(AlGa) As quantum-well structures at low temperature

Photoluminescence experiments at low temperatures have revealed the existence of a previously unreported feature on the high-energy side of the $n=1$ (e-HH) $1s$ exciton recombination from GaAs-(AlGa) As multiple-quantum-well structures. Detailed circular-polarization and excitation-spectroscopy measurements have led to this feature being assigned to recombination of $n=1$ (e-HH) $2s$ excitons and free electron-hole pairs in the lowest subbands. In our samples, where there is no Stokes shift of the exciton lines, the energetic position of this peak relative to the main luminescence line gives a reliable measurement of the $n=1$ (e-HH) $1s$ exciton binding energy as a function of quantum-well width.