Threshold photogeneration of biexcitons in direct-gap semiconductor nanocrystals

The generation of two electron–hole pairs (a biexciton) in a nanocrystal of a direct-gap semiconductor with a nondegenerate conduction band upon the absorption of a single photon with the energy equal to twice the band gap of the nanocrystal is considered. It is shown that the process can take place only in the presence of the interaction of electrons both with each other and with the crystal-lattice field. The rate of this process is calculated and found to depend strongly on the nanocrystal size.