COHERENCE AND LOCALIZATION IN SUPERLATTICES UNDER ELECTRIC-FIELDS

Using optical techniques, we have demonstrated that the quantum coherence of electron states in GaAsGaAlAs superlattices under electric fields increases drastically as the period, D, and the electric field, ∄, decrease, reaching at least ten periods at zero field when D = 60 A ̊. The electric field localizes the states, breaking the superlattice minibands into Stark ladders, and producing a transition from three- to quasi-two-dimensional excitons. These effects are manifested, respectively, by the appearance of oscillations in the absorption coefficient, which are periodic both in energy and in ∄-1, and by a sharp increase in the intrawell exciton binding energy. © 1990.