  We propose and evaluate the vertical cascade terahertz and infrared
photodetectors based on multiple-graphene-layer (GL) structures with thin
tunnel barrier layers (made of tungsten disulfide or related materials). The
photodetector operation is associated with the cascaded radiative electron
transitions from the valence band in GLs to the conduction band in the
neighboring GLs (interband- and inter-GL transitions). We calculate the
spectral dependences of the responsivity and detectivity for the vertical
cascade interband GL- photodetectors (I-GLPDs) with different number of GLs and
doping levels at different bias voltages in a wide temperature range. We show
the possibility of an effective manipulation of the spectral characteristics by
the applied voltage. The spectral characteristics depend also on the GL doping
level that opens up the prospects of using I-GLPDs in the multi-color systems.
The advantages of I-GLPDs under consideration are associated with their
sensitivity to the normal incident radiation, weak temperature dependence of
the dark current as well as high speed of operation. The comparison of the
proposed I-GLDs with the quantum-well intersubband photodectors demonstrates
the superiority of the former, including a better detectivity at room
temperature and a higher speed. The vertical cascade I-GLDs can also surpass
the lateral p-i-n GLDs in speed.
