  We propose and evaluate the graphene layer (GL) infrared photodetectors
(GLIPs) based on the van der Waals (vdW) heterostructures with the radiation
absorbing GLs. The operation of the GLIPs is associated with the electron
photoexcitation from the GL valence band to the continuum states above the
inter-GL barriers (either via tunneling or direct transitions to the continuum
states). Using the developed device model, we calculate the photodetector
characteristics as functions of the GL-vdW heterostructure parameters. We show
that due to a relatively large efficiency of the electron photoexcitation and
low capture efficiency of the electrons propagating over the barriers in the
inter-GL layers, GLIPs should exhibit the elevated photoelectric gain and
detector responsivity as well as relatively high detectivity. The possibility
of high-speed operation, high conductivity, transparency of the GLIP contact
layers, and the sensitivity to normally incident IR radiation provides
additional potential advantages in comparison with other IR photodetectors. In
particular, the proposed GLIPs can compete with unitravelling-carrier
photodetectors.
