  The distribution of rates of carrier multiplication (CM) following photon
absorption is calculated for semiconductor nanocrystals (NCs). The NC
electronic structure is described using a screened pseudopotential method known
to give reliable description of NC excitons. The rates of biexciton generation
are calculated using the Fermi golden rule with all relevant Coulomb matrix
elements, taking into account proper selection rules. In CdSe and InAs NCs we
find a broad distribution biexciton generation rates depending strongly on the
exciton energy and size of the NC. The process becomes inefficient for NC
exceeding 3 nm in diameter in the photon energy range of 2-3 times the band
gap.
