Discrete self-oscillation period branches observed in semiconductor superlattices

We investigate the self-sustained current oscillation of a weakly coupled semiconductor superlattice in the dynamical voltage band using a microscopic sequential tunneling model. With the voltage as a control parameter, two types of branches of current oscillation period versus voltage have been observed, which correspond to various oscillation scenarios. The first branch type consists of a series of period branches in accordance with how many charge dipoles need to be created at the emitter side to trigger a dipole-tripole oscillation scenario. For the second branch type, charge dipoles are generated periodically at the emitter, but all of them fail to develop completely and die out, thereby leading to a low-period oscillation scenario without the dipole-tripole process. The bistability between different branches is also observed by voltage up-sweeping and down-sweeping.