  We performed Cu {\it K}-edge X-ray absorption fine structure measurements on
T'-type La$_{1.8}$Eu$_{0.2}$CuO$_4$ (LECO) and Nd$_2$CuO$_4$ (NCO) to
investigate the variation in the electronic state associated with the emergence
of superconductivity due to annealing. The X-ray absorption near-edge structure
spectra of as-sintered (AS) LECO are quite similar to those of AS NCO,
indicating that the ground state of AS T'-type LECO is a Mott insulator. We
found a significant variation of the electronic state at the Cu sites in LECO
due to annealing. The electron density after annealing ($n_{\rm AN}$) was
evaluated for both superconducting LECO and non-superconducting NCO and found
to be 0.40 and 0.05 electrons per Cu, respectively. In LECO but not in NCO,
extended X-ray absorption fine structure analysis revealed a softening in the
strength of the Cu-O bond in the CuO$_2$ plane due to annealing, which is
consistent with the screening effect on phonons in the metallic state. Since
the amounts of oxygen loss due to annealing ($\delta$) for LECO and NCO are
comparable with each other, these results suggest distinct electron-doping
processes in the two compounds. That electron-doping in NCO approximately
follows the relation $n_{\rm AN}=2\delta$ can be understood if electrons are
doped through oxygen deficiency, but the anneal-induced metallic nature and
large $n_{\rm AN}$ of LECO suggest a variation of the electronic band structure
causes self-doping of carriers. The origin of the difference in doping
processes due to annealing is discussed in connection with the size of the
charge transfer gap.

Superconductivity;Strongly Correlated Electrons