Stark localization in GaAs-GaAlAs superlattices under an electric field

We have observed that a strong electric field E shifts to higher energies the photoluminescence and photocurrent peaks of a GaAs-Ga0.65Al0.35As superlattice of period D (=65), which we explain by a field-induced localization of carriers to isolated quantum wells. Good agreement is found between observed and calculated shifts when the large field-induced increase of the exciton binding energy is taken into account. At moderate fields [(2-3)×104 V/cm], the coupling between adjacent wells is manifested by four additional peaks that shift at the rates ± eED and ± 2eED and correspond to transitions that involve different levels of the Stark ladder.