Exciton dephasing and biexciton binding in CdSe/ZnSe islands

The dephasing of excitons and the formation of biexcitons in self-organized CdSe/ZnSe islands grown by molecular-beam epitaxy is investigated using sp ectrally resolved four-wave mixing. A distribution of exciton-exciton scatt ering efficiencies and dephasing times in the range of 0.5-10 ps are observ ed. This indicates the presence of differently localized exciton states at comparable transition energies. Polarization-dependent measurements identif y the formation of biexcitons with a biexciton binding energy of more than four times the bulk value. With decreasing exciton energy, the binding ener gy slightly increases from 21.5 to 23 meV, while its broadening decreases f rom 5.5 to 3 meV. This is attributed to a strong three-dimensional confinem ent with improving shape uniformity for decreasing exciton energy. [S0163-1 829(99)04739-6].