We report the observation of bifurcation patterns in the frequency spectra of current self-oscillations in an undoped, photoexcited GaAs/AlAs superlattice modulated by an external ac driving voltage. The ac frequency was adjusted to the goldenmean times the fundamental frequency of the current self-oscillations. These bifurcation patterns exhibit transitions between periodic and chaotic oscillations as a function of the amplitude of the external driving voltage. A change in the laser intensity results in a very different bifurcation pattern indicating that these patterns are also strongly dependent on the carrier density.
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