  Angle-resolved photoemission spectroscopy (ARPES) reveals effects of electron
doping, which is realized by Co and Ni substitution for Fe in
FeTe$_{1-y}$Se$_{y}$ (y$\sim$0.35) superconductor. The data show consistent
band shifts as well as expansion and shrinking of electron and hole Fermi
surface, respectively. Doping of either element leads to a Lifshitz transition
realized as a removal of one or two hole pockets. This explains qualitatively a
complex behavior of Hall coefficient observed before [Bezusyy, et al., Phys.
Rev. B 91, 100502 (2015)], including change of sign with doping, which takes
place only below room temperature. Assuming that Ni substitution should deliver
twice more electrons to the valence band than Co, it appears that such transfer
is slightly more effective in the case of Co. Therefore, charge doping cannot
account for much stronger effect of Ni on superconducting and transport
properties [Bezusyy, et al., Phys. Rev. B 91, 100502 (2015)]. Although overall
band shifts are roughly proportional to the amount of dopant, clear deviations
from a rigid band shift scenario are found. The shape of electron pockets
becomes elliptical only for Ni doping, effective mass of electron bands
increases with doping, strong reduction of effective mass is observed for one
of hole bands of the undoped system. The topology of hole and electron pockets
for superconducting Fe$_{1.01}$Te$_{0.67}$Se$_{0.33}$ with T$_{c}$=13.6 K
indicates a deviation from nesting. Co and Ni doping causes further departure
from nesting, which accompanies the reduction of critical temperature.
