  The current responsivity of a semiconductor superlattice THz-photon detector
is calculated using an equivalent circuit model which takes into account the
finite matching efficiency between a detector antenna and the superlattice in
the presence of parasitic losses. Calculations performed for currently
available superlattice diodes show that both the magnitudes and the roll-off
frequencies of the responsivity are strongly influenced by an excitation of
hybrid plasma-Bloch oscillations which are found to be eigenmodes of the system
in the THz- frequency band. The expected room temperature values of the
responsivity (2-3 A/W in the 1-3 THz-frequency band) range up to several
percents of the quantum efficiency $e/\hbar\omega$ of an ideal superconductor
tunnel junction detector. Properly designed semiconductor superlattice
detectors may thus demonstrate better room temperature THz-photon responsivity
than conventional Schottky junction devices.
