We have observed an electric-field-induced change in the dimensionality of excitons in superlattices, from three to quasi-two dimensions. The exciton binding energy of a (40 Å)/(40 Å) GaAs/(GaAl)As superlattice, determined from low-temperature photocurrent experiments, increases more than 6 meV by the action of an electric field perpendicular to the superlattice layers. This sharp increase, from nearly the bulk value of GaAs at very low fields to the isolated-quantum-well value at high fields, is a direct consequence of the Stark localization of electrons and holes in superlattices.

• Received 11 August 1989

DOI:https://doi.org/10.1103/PhysRevB.41.1676