Geometric approach to determine the binding energy of quasi-two-dimensional biexcitons

We improve upon the simple method of Singh et al. [Phys. Rev. B 53, 15 909 (1996)] to calculate the biexciton binding energy in quasi-two-dimensional (2D) quantum wells. Optimizing the geometric configuration, a simple and an alytical expression for the ratio of the binding energy of a 2D biexciton t o that of an exciton, E-b(xx)/E-b(x), is derived. It is found that the geom etric configuration of a positronium-molecule-like biexciton is a square an d that of a hydrogen-molecule-like biexciton is a tetragon. The average int erparticle distances as functions of sigma are also determined. The theory is applied to GaAs, ZnSe, and CdxZn1-xSe quantum wells and the result of E- b(xx)/E-b(x) thus obtained agrees with the experimental results. [S0163-182 9(99)14827-6].