Abstract
We observed the phonons emitted by a two-dimensional electron gas in GaAs/AlGaAs heterojunctions for various carrier concentrations, by a nanosecond pulse technique. We found that the feature which has usually been regarded as the crossover from acoustic to optic phonon emission then occurred at different power levels. We propose that a process of energy loss via excitation of coupled plasmon–optic phonon modes can explain this and other results, notably the weakness of the longitudinal mode observed, and the high value of the measured energy loss.