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 various confinements. It is found that the biexciton binding energy drops sharply 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). Prom E(b)/(xx) = 0, we obtain R(C) ~ 0.5a(B)/(*), indicating the existence of a repulsive 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 thickness is also investigated.