  We analyze the nonlinear carrier transport in the gated graphene-phosphorene
(G-P) hybrid structures - the G-P field-effect transistors (G-P-FETs) using a
phenomenological model. This model assumes that due to high carrier densities
in the G-P-channel, the carrier system, including the electrons and holes in
both the G- and P-layers, is characterized by a single effective temperature.
We demonstrate that a strong electric-field dependence of the G-P-channel
conductivity and substantially non-linear current-voltage characteristics,
exhibiting a negative differential conductivity, are associated with the
carrier heating and the real-space carrier transfer between the G- and
P-layers. The predicted features of the G-P-systems can be used in the
detectors and sources of electromagnetic radiation and in the logical circuits.
