BLOCH OSCILLATIONS, ZENER TUNNELING, AND WANNIER-STARK LADDERS IN THE TIME-DOMAIN

We present a time-domain analysis of carrier dynamics in a semiconductor superlattice with two minibands. Integration of the density-matrix equations of motion reveals a number of new features: (i) for certain values of the applied static electric field strong interminiband transitions occur; (ii) in static fields the complex time dependence of the density matrix displays a sequence of stable plateaus in the low field regime, and (iii) for harmonic fields the Fourier representation of the density matrix is shown to be intimately related to the quasienergy spectrum. © 1995 The American Physical Society.