MODULATION OF WANNIER-STARK TRANSITIONS BY MINIBAND FRANZ-KELDYSH OSCILLATIONS IN STRONGLY COUPLED GAAS-ALAS SUPERLATTICES

We present calculations and optical experiments performed at 77 K on a GaAs/AlAs superlattice with only one monolayer AlAs barriers and a combined miniband width of 380 meV. In particular the field dependent transition from the 3D miniband system to the 2D Wannier Stark (WS) regime is investigated. Using Differential Photocurrent Spectroscopy we are able to resolve WS transitions with indices n between -9 and +9. At the same time Franz-Keldysh (FK) oscillations are observable at the lower and for the first time even at the upper miniband edge. A modulation of the WS transitions by the FK oscillations (and vice versa) is clearly visible. Our theory describes in detail the competition of the linear WS fan originating at the ''center of mass energy'' with the non-linear fans of the FK oscillations evolving from the lower and upper miniband edges.