  The heating of carriers in an intrinsic graphene under an abrupt switching
off a dc electric field is examined taking into account both the energy
relaxation via acoustic and optic phonons and the interband
generation-recombination processes. The later are caused by the interband
transitions due to optical phonon modes and thermal radiation. Description of
the temporal and steady-state responses, including the nonequilibrium
concentration and energy as well as the current-voltage characteristics, is
performed. At room temperature, a nearly-linear current-voltage characteristic
and a slowly-varied concentration take place for fields up to -- 20 kV/cm.
Since a predominant recombination of high-energy carriers due to optical phonon
emission at low temperatures, a depletion of concentration takes place below --
250 K. For lower temperatures the current tends to be saturated and a negative
differential conductivity appears below -- 170 K in the region of fields -- 10
V/cm.
