  We evaluate the terahertz (THz) detectors based on field effect transistor
(FET) with the graphene channel {GC} and a floating metal gate (MG) separated
from the GC by a black-phosphorus (b-P) or black-arsenic (b-As) barrier layer
(BL). The operation of these GC-FETs is associated with the heating of the
two-dimensional electron gas in the GC by impinging THz radiation leading to
thermionic emission of the hot electrons from the GC to the MG. This results in
the variation of the floating gate potential, which affects the source-drain
current. At the THz radiation frequencies close to the plasmonic resonance
frequencies in the gated GC, the variation of the source-drain current and,
hence, the detector responsivity can be resonantly large.
