  Excitonic contributions to absorption and photocurrent generation in
semiconductor nanostructures are described theoretically and simulated
numerically using steady-state non-equilibrium Green's function theory. In a
first approach, the coherent interband polarization including Coulomb
corrections is determined from a Bethe-Salpeter-type equation for the equal
time interband single-particle charge carrier Green's function. The effects of
excitonic absorption on photocurrent generation are considered on the same
level of approximation via the derivation of the corresponding corrections to
the electron-photon self-energy.
