Absolute Instability in Superlattice Miniband Transport

The possible absolute instability in superlattice miniband transport using the hydrodynamic balance equations for arbitrary energy dispersion is investigated. In contrast to the prediction of the drift-diffusion model that in doped semiconductor superlattices absolute instability occurs closely following the onset of negative differential mobility (NDM), the present analysis shows that a wide-miniband planar superlattice may become absolutely unstable only when it is biased deep in the NDM regime. This result is in agreement with recent experimental findings.