SUPPRESSION OF ABSOLUTE INSTABILITY BY ELASTIC-SCATTERING IN SEMICONDUCTOR SUPERLATTICES

Absolute instabilities of planar semiconductor superlattices exhibitin g negative differential mobility (NDM) in vertical transport are inves tigated using the three-dimensional hydrodynamic balance equations for arbitrary energy dispersion, with an accurate microscopic treatment o f phonon and impurity scatterings. In contrast with the prediction of the drift diffusion model that in doped semiconductor superlattices ab solute instability occurs closely following the onset of NDM, the pres ent analysis shows that a planar superlattice may become absolutely un stable only when it is biased within a range deep in the NDM regime, a nd 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 diffus ion model.