The formation of spatially indirect excitons in superlattices with nar
row minibands is investigated experimentally. The interwell exciton is
similar to the first Wannier-Stark localized exciton of an electrical
ly biased superlattice. However, in the present case the localization
is mediated by the Coulomb interaction of the electron and the hole wi
thout external fields. (C) 1997 Academic Press Limited.