Anomaly of the current self-oscillation frequency in the sequential tunneling of a doped GaAs/AlAs superlattice

An anomalous behavior of the current self-oscillation frequency is observed in the dynamic de voltage bands, emerging from each sawtoothlike branch of the current-voltage characteristic of a doped GaAs/A1As superlattice in th e transition process from static to dynamic electric field domain formation s. Varying the applied de voltage at a fixed temperature, we find that the frequency increases while the averaged current decreases. Inside each volta ge band, the frequency has a strong voltage dependence in the temperature r ange where the averaged current changes with the applied de voltage. This d ependence can be understood in terms of motion of the system along a limit cycle.