Suppression of absolute instability by elastic scattering in semiconductor superlattices

Abstract

Absolute instabilities of planar semiconductor superlattices exhibiting negative differential mobility (NDM) in vertical transport are investigated using the three-dimensional hydrodynamic balance equations for arbitrary energy dispersion, with an accurate microscopic treatment of phonon and impurity scatterings. In contrast with the prediction of the drift diffusion model that in doped semiconductor superlattices absolute instability occurs closely following the onset of NDM, the present analysis shows that a planar superlattice may become absolutely unstable only when it is biased within a range deep in the NDM regime, and the enhancement of the elastic scattering suppresses the occurrence of the absolute instability. This result is in agreement with recent experimental findings, which cannot be explained within a drift diffusion model.