  A graphene sheet partially covered with a bulk superconductor serves as a
normal conductor--superconductor (NS) junction, in which electron transport is
mainly governed by Andreev reflection (AR). As excess carriers induced over the
covered region penetrate into the uncovered region over a screening length, the
charge neutrality point (CNP) in the uncovered region shifts only near the NS
interface. We theoretically study the electron transport in a bilayer graphene
junction taking account of such spatial variation of the CNP in the
electron-doped case. When the Fermi level is close to the CNP away from the NS
interface, the AR takes place in a specular manner owing to the diffraction of
a reflected hole occurring at a $pn$ junction, which is naturally formed in the
uncovered region. It is shown that the differential conductance shows an
unusual asymmetric behavior as a function of bias voltage under the influence
of the $pn$ junction. It is also shown that, if the Fermi level is located
below the CNP, the $pn$ junction gives rise to quasi-bound states near the NS
interface, leading to the appearance of resonant peaks in the differential
conductance.
