Step-by-step evolution from Franz-Keldysh oscillations to Stark-Wannier confinement in anIn0.12Ga0.88As/GaAs superlattice

We report 77-K modulated transmission measurements on an ${\mathrm{In}}_{0.12}$ ${\mathrm{Ga}}_{0.88}$As/GaAs 100-Å-period superlattice as a function of a variable, uniform, external dc field. The spectra evolve continuously as the field increases from a Franz-Keldysh regime to Stark-Wannier confinement, passing through an intermediate-field region whose precise theoretical description has not yet been formulated. In this way the step-by-step evolution of the electronic states as a function of the external field has been documented.