Excitons in type-II quantums dots: Binding of spatially separated electron and hole.

The quantum size effect for the binding energy of an exciton in a spherical quantum dot is studied theoretically. We use a variational approach and assume that the electron and hole are separated by infinite offsets. The dependence of the exciton binding energy upon the dot radius 12 is calculated for various sets of hole and electron effective masses. The spatial structure of the bound electron-hole pair is qualitatively different in the two regimes in which the dot radius 12 is either much smaller or much larger than an effective Bohr radius of the exciton in bulk