Stark localization in GaAs-GaAlAs superlattices under an electric field.

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 \AA{}), 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 [\ensuremath{\cong}(2-3)\ifmmode\times\else\texttimes\fi{}${10}^{4}$ V/cm], the coupling between adjacent wells is manifested by four additional peaks that shift at the rates $\ifmmode\pm\else\textpm\fi{}e\mathcal{E}D$ and $\ifmmode\pm\else\textpm\fi{}2e\mathcal{E}D$ and correspond to transitions that involve different levels of the Stark ladder.