Terahertz detection using excitations of plasmon modes offers a high-speed, high resolution, and frequency-selective
alternative to existing technology. Plasmons in high mobility quantum well two-dimensional electron gas (2DEG)
systems can couple to radiation when either the channel carrier density, or the incident radiation, is spatially modulated
with appropriate periodicity. Grating-gated terahertz detectors having a voltage tunable frequency response have been
developed based on this principle. A continuous wave THz photomixer was used to characterize the resonant absorption
in such devices. At the fundamental 2DEG plasmon frequency, defined by the grating and the quantum well carrier
density, a 20% change in transmission was observed. As the resonance is tuned from the 'natural' plasmon frequency
through application of a gate bias, it shifts as expected, but the transmission change drops to only a few percent.