Current-voltage characteristic, stability, and self-sustained current   oscillations in resonant-tunneling n-doped semiconductor superlattices
  We review the statics and dynamics of electric-field domains on doped superlattices within a discrete drift model. A complete analysis of the construction and stability of stationary field profiles having two domains is carried out. As a consequence we determine the intervals of doping on which self-sustained current oscillations may appear under dc voltage bias. We have also studied the influence of doping, boundary condition and length of the superlattice on the self-sustained oscillations. Our study shows that there are bistability regions where either self-sustained current oscillations or steady states are reached depending on the initial condition. For a wide bias interval, the self-sustained oscillations are due to the formation, motion and recycling of electric-field domain walls inside the superlattice. There are biases (typically in the region of bistability) for which the strength of the high and low field domains changes periodically in time while the domain wall remains almost pinned on a few quantum wells. 
L.L.Bonilla, M. Kindelan, M. Moscoso, and A. Wacker