Longitudinal Coulomb attraction in coupled quantum wells

It is shown that Coulomb attraction between electron and hole in coupled quantum wells leads to localization of states in the direction of growth, i.e., in one of the wells, even when the wells are symmetric and unbiased. As a result, oscillator strength of the lowest excitonic transition can increase by more than 100%, while the oscillator strengths of higher-energy transitions can decrease. These results, obtained using recently developed models, are important for an understanding of the Wannier-Stark localization effect in quantum wells and superlattices.