Abstract

We investigated the current-voltage I(V) characteristics of GaAs/AlAs double-barrier heterostructures. A fine periodic structure of the resonant tunnel current has been revealed. We attribute it to a sequence of the collective excitations, presumably of the coupled plasmon-phonon type, that are induced in the heavily doped collector region by hot electrons which escape from the quantum well. An oscillatory structure appears also in the valley regions of the I(V) curve under a high magnetic field parallel to the current. It is due to the off-resonance tunnelling between the Landau-quantized states of the emitter and quantum well. Particular phonon-assisted processes in the tunnelling have been identified.