High-electric-field quantum transport theory for semiconductor superlattices

Nonlinear quantum transport in semiconductor superlattices (SLs) is studied based on the Kadanoff-Baym-Keldysh non-equilibrium Green function technique. Emphasis is placed on quantum box SLs with a discrete energy spectrum. Special results are obtained for the highfield transport of a one-dimensional SL model. Both intra-collisional field effects and lifetime broadening are treated self-consistently on an equal footing. For narrow miniband SLs exact results are derived for the field and temperature dependence of the current density, which even differ qualitatively from those obtained by making use of the generalized Kadanoff-Baym ansatz. The rigorous quantum mechanical treatment reveals the hopping character of the transport in narrow miniband SLs. This is compared with results derived from the density-matrix approach.