We have observed that a strong electric field $\mathcal{E}$ shifts to higher energies the photoluminescence and photocurrent peaks of a GaAs-${\mathrm{Ga}}_{0.65}$${\mathrm{Al}}_{0.35}$As superlattice of period $D$ (=65 Å), 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)×${10}^4$ V/cm], the coupling between adjacent wells is manifested by four additional peaks that shift at the rates $\pm e\mathcal{E}D$ and $\pm 2e\mathcal{E}D$ and correspond to transitions that involve different levels of the Stark ladder.

• Received 21 January 1988

DOI:https://doi.org/10.1103/PhysRevLett.60.2426