Optical control of the two-dimensional electron-gas density in modulation-doped quantum wells studied by magnetophotoluminescence

We show by magnetoluminescence and photoluminescence excitation spectroscopy that the density of the two-dimensional electron gas in a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As asymmetric modulation-doped multiple quantum-well structure is changed when the sample is excited with photons having an energy lower than the alloy band gap.