Dynamics of the electron–hole correlation in femtosecond pulse excited semiconductors

We study the temporal evolution of the spatial electron–hole correlation after a resonant femtosecond (fs) pulse excitation. The probability of finding an electron and hole at a distance r peaks at r=0, because the absorption process creates the electron–hole pair at the same position but with opposite momenta. The correlation extends also for unbound electron–hole pairs over a sphere with roughly an exciton Bohr radius. Due to the resulting drift, but also due to carrier–carrier and carrier–LO-phonon scattering, the original correlation decreases in about 100 fs and approaches its constant value. The evolution of the electron–hole correlation is calculated within the semiconductor Bloch equations with quantum kinetic scattering integrals due to time-dependently screened Coulomb and LO-phonon scattering integrals.