Direct biexciton generation in Si nanocrystal by a single photon

It has been shown theoretically that strong quantum confinement regime in Si nanocrystals promotes the highly efficient simultaneous excitation of two electron-hole pairs (biexciton) by a single photon. The rate (inverse lifetime) of biexciton generation has been calculated analytically as function of the nanocrystal radius. In contrast to the case of a nanocrystal formed of direct-band-gap semiconductor, the size-dependence of the rate in Si nanocrystal turns out to be sharp enough. At radii approaching a nanometer, the lifetime of biexciton generation falls into the nanosecond range.