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 techniqu e. Emphasis is placed on quantum box SLs with a discrete energy spectrum. S pecial results are obtained for the highfield transport of a one-dimensiona l SL model. Both intra-collisional field effects and lifetime broadening ar e treated self-consistently on an equal footing. For narrow miniband SLs ex act results are derived for the field and temperature dependence of the cur rent density, which even differ qualitatively from those obtained by making use of the generalized Kadanoff-Baym ansatz. The rigorous quantum mechanic al treatment reveals the hopping character of the transport in narrow minib and SLs. This is compared with results derived from the density-matrix appr oach.