General analysis of instabilities and oscillations of the sequential tunneling in superlattices

We present a general analysis of instabilities and oscillations of the sequential tunneling current in superlattices, based on the current-voltage characteristic of a single barrier. Our results depend only on the presence of a negative differential resistance region and are independent of the details of the model. We establish general conditions for the existence of a stable oscillatory region of current-voltage characteristic of the superlattice, and for instability leading to current self-oscillation. Our formalism permits a natural connection to standard results of chaos theory. [S0163-1829(99)50520-1].