Observation of the Wannier-Stark Quantization in a Semiconductor Superlattice

When an electric field $F$ is applied parallel to the growth axis of a semiconductor superlattice, the eigenstates are quantized and strongly localized. This Wannier-Stark quantization manifests itself as an effective blue shift of the optical-absorption edge and is accompanied by a new type of electro-optical oscillation of the absorption coefficient which is periodic in $F^{-1\mathrm{}}$. We report experimental evidences for these theoretical predictions from the study of the low-temperature electroreflectance of a GaAs-AlGaAs superlattice.