Current self-oscillations and chaos in semiconductor superlattices

The nonlinear transport properties of weakly coupled superlattices have been investigated by measuring real-time current traces and frequency spectra. Current self-oscillations are observed for the undriven system by simply applying a dc voltage. Doped superlattices as well as photoexcited undoped superlattices can exhibit self-oscillations of the current. When the system is driven with an external ac voltage in addition to the dc voltage, the superlattices exhibit frequency-locked, quasiperiodic, and chaotic windows as a function of the amplitude of the driving voltage.