INTERWELL EXCITONS IN GAAS SUPERLATTICES

The formation of spatially indirect excitons in superlattices with nar row minibands is theoretically and experimentally investigated. We ide ntify the experimental conditions for the observation of interwell exc itons and find a distinct excitonic state energetically located betwee n the Is exciton and the onset of the miniband absorption. The interwe ll exciton is similar to the first Wannier-Stark localized exciton of on electrically biased superlattice. However. in the present case the localization is mediated by the Coulomb interaction of the electron an d the hole without external fields.