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 R 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 R is either much smaller or much larger than an effective Bohr radius of the exciton in bulk.