Binding energy of the biexcitons in isotropic semiconductors

The dependence of the binding energy W of the biexciton on the electronhole mass ratio σ is discussed. The bounds from above and from below on the possible curves y = W (σ) have been obtained. In particular, the upper bound implies a positive binding of the biexcitons in the whole interval of the parameter σ. The bounds on W (σ) have been compared with experimental results on biexcitons in semiconductors.