SEMICONDUCTOR SUPERLATTICE EXCITON-STATES IN CROSSED ELECTRIC AND MAGNETIC-FIELDS

We present a formalism for the calculation of exciton energies and abs orption strengths in superlattices in the presence of a static in-plan e magnetic field and a static along-axis electric field. The formalism is necessarily very different from that used for the calculation of s ingle-particle states in the same configuration, due to the very diffe rent symmetries of the single-particle and exciton Hamiltonians. We fi nd exciton Stark ladder states when an electric field is applied, exci ton Landau levels when a magnetic field is applied, and we observe an interesting competition between the two fields when both are applied. We obtain good agreement with experimental photocurrent and photolumin escence excitation results for a number of small-period structures, an d provide simple physical explanations for some of the experimentally observed results which were hitherto only partially understood. The ca lculation also yields exciton states with appreciable oscillator stren gth which have no single-particle analog, but for which there is exper imental evidence.