DENSITY OF STATES AND WANNIER-STARK LEVELS OF SUPERLATTICES IN AN ELECTRIC-FIELD

The density of states is calculated for superlattices in the presence of an electric field, using the concept of a generalized transmission probability. Various Ga1-xAlxAs-based quantum-well structures with up to 200 periods are examined for electric fields ranging from 4 X 10(2) V/CM to 1 X 10(6) V/CM. Different field effects are observed in the b elow- and above-barrier regions of the density-of-states spectra. In t he below-barrier region the spectra embody the occurrence of Wannier-S tark localization. The above-barrier region is dominated by two kinds of structures, one similar to Franz-Keldysh oscillations, and another resembling a Wannier-Stark-ladder behavior.