  In order to characterize magnetic-field (B) tunable THz plasmonic detectors,
spectroscopy experiments were carried out at liquid helium temperatures and
high magnetic fields on devices fabricated on a high electron mobility
GaAs/AlGaAs heterostructure. The samples were either gated (the gate of a
meander shape) or ungated. Spectra of a photovoltage generated by THz radiation
were obtained as a function of B at a fixed THz excitation from a THz laser or
as a function of THz photon frequency at a fixed B with a Fourier spectrometer.
In the first type of measurements, the wave vector of magnetoplasmons excited
was defined by geometrical features of samples. It was also found that the
magnetoplasmon spectrum depended on the gate geometry which gives an additional
parameter to control plasma excitations in THz detectors. Fourier spectra
showed a strong dependence of the cyclotron resonance amplitude on the
conduction-band electron filling factor which was explained within a model of
the electron gas heating with the THz radiation. The study allows to define
both the advantages and limitations of plasmonic devices based on high-mobility
GaAs/AlGaAs heterostructures for THz detection at low temperatures and high
magnetic fields.
