  We study nuclear spin polarization in the quantum Hall regime through the
optically pumped electron spin polarization in the lowest Landau level. The
nuclear spin polarization is measured as a nuclear magnetic field $B_N$ by
means of the sensitive resistive detection. We find the dependence of $B_N$ on
filling factor unmonotonous. The comprehensive measurements of $B_N$ with the
help of the circularly polarized photoluminescence measurements indicate the
participation of the photo-excited complexes i.e., the exciton and trion
(charged exciton), in nuclear spin polarization. On the basis of a novel
estimation method of the equilibrium electron spin polarization, we analyze the
experimental data and conclude that the filling factor dependence of $B_N$ is
understood by the effect of electron spin polarization through excitons and
trions.
