  Formation of localized impurity levels within the band gap in bigraphene
under applied electric field is considered and the conditions for their
collectivization at finite impurity concentration are established. It is shown
that a qualitative restructuring of quasiparticle spectrum within the initial
band gap and then specific metal-insulator phase transitions are possible for
such disordered system and can be effectively controlled by variation of the
electric field bias at given impurity perturbation potential and concentration.
Since these effects can be expected at low impurity concentrations but at not
too low temperatures, they can be promising for practical applications in
nanoelectronics devices.
