  We study theoretically the coexistence of the spin-density-wave (SDW) and
superconductivity in electron-doped iron-pnictide superconductors based on the
two orbital model and Bogoliubov-de Gennes equations. The phase diagram is
mapped out and the evolution of the Fermi surface as the doping varies is
presented. The local density of states (LDOS) has also been calculated from low
to high doping. We show that the strength of the superconducting coherent peak
at the positive energy gets enhanced and the one at the negative energy is
suppressed by the SDW order in the underdoped region. Several features of our
results are in good agreement with the experiments.
