  A variational calculation of the ground state energy of a biexciton in a
GaAs/AlGaAs quantum well is presented. The well width fluctuations leading to
trapping of the biexcitons are modeled by a parabolic potential. The results
obtained for different well widths are compared with recent experimental data.
Good agreement is obtained both for the biexciton binding energy and for the
Haynes factor. We find that the structure of a biexciton is similar to the one
of the H_2 molecule.
