Anomaly of the current self-oscillation frequency in the sequential tunneling of a doped GaAsÕAlAs superlattice

An anomalous behavior of the current self-oscillation frequency is observed in the dynamic dc voltage bands, emerging from each sawtoothlike branch of the current-voltage characteristic of a doped GaAs/AlAs superlattice in the transition process from static to dynamic electric field domain formations. Varying the applied dc voltage at a fixed temperature, we find that the frequency increases while the averaged current decreases. Inside each voltage band, the frequency has a strong voltage dependence in the temperature range where the averaged current changes with the applied dc voltage. This dependence can be understood in terms of motion of the system along a limit cycle.