Scattering times in two-dimensional systems determined by tunneling spectroscopy

On GaAs-${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructures, resonant-tunneling processes between two coupled two-dimensional systems are investigated as a function of illumination. With increasing level of illumination, the subband energies and the corresponding spacings between the observed subband resonance peaks are decreased through a reduced depletion field. In addition, large LO-phonon-related satellites of the original subband resonances are observed, which indicate that LO-phonon-assisted processes are the dominant scattering mechanisms in this regime. At high depletion fields, however, electron-plasmon interaction turns out to be the relevant scattering process. Using the amplitude of the phonon satellites as a reference, the field-dependent scattering rate for this process is determined experimentally.