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

We present a formalism for the calculation of exciton energies and absorption strengths in superlattices in the presence of a static in-plane magnetic field and a static along-axis electric field. The formalism is necessarily very different from that used for the calculation of single-particle states in the same configuration, due to the very different symmetries of the single-particle and exciton Hamiltonians. We find exciton Stark ladder states when an electric field is applied, exciton 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 photoluminescence excitation results for a number of small-period structures, and provide simple physical explanations for some of the experimentally observed results which were hitherto only partially understood. The calculation also yields exciton states with appreciable oscillator strength which have no single-particle analog, but for which there is experimental evidence.