Binding energy of biexcitons in a quantum disk

The method of few-body physics is applied to treat a system of two excitons in a quantum disk. The binding energy of a biexciton is calculated for var ious confinements. It is found that the biexciton binding energy drops shar ply to zero, i.e. there exists a critical radius R-C, such that if R > R-C (R < R-C), the biexciton configuration is stable (unstable). From E-b(xx) = 0, we obtain R-C similar to 05a(B)*, indicating the existence of a repulsi ve core of interaction between the two neutral excitons. The dependence of the ratio of biexciton binding energy to that of the exciton on the disk th ickness is also investigated.