Tripole current oscillations in superlattices

Based on a microscopic sequential tunneling model, we analyze the dynamical evolution of the charge density in a superlattice (SL) for fixed external voltage in the regime of self-sustained current oscillations. We find oscillations which involve two accumulation layers and one depletion layer simultaneously (tripole oscillations). Depending on the external voltage, two different scenarios are possible. For low voltages, all three charge monopoles (fronts) traverse the SL from the emitter to the collector, while for higher voltages, the depletion front catches up with the leading accumulation front, and both annihilate.