When a double barrier semiconductor structure is biased near a tunneli
ng resonance, charge can accumulate in the quantum well. Coupling betw
een this two dimensional electron gas and the tunneling current is inv
estigated. Experimental data taken inside a region of apparent bistabi
lity in one device reveal a satellite on the high energy side of the c
urrent resonance in the I(V) characteristic. A theoretical model based
on the many-body transfer Hamiltonian formalism shows that a plasmon
excitation has a remarkably similar structure. Magnetic field data sup
port the plasmon satellite interpretation.