4. Realization of Resonant Plasmon Excitation and Detection

The effect of symmetries in the terahertz field distribution and the field-effect channel on terahertz photocurrent is examined and compared to the quasi-static field-effect detector model. Resonant excitation of cavity plasmon modes and nonresonant self-mixing of terahertz waves are demonstrated in an AlGaN/GaN two-dimensional electron gas with symmetrically designed nanogates, antennas, and filters. We found that the self-mixing signal can be effectively suppressed by the symmetric design and the resonant response benefits from the residual asymmetry. The findings further confirm the quasi-static field-effect detector model. The findings also suggest that a single detector may provide both a high sensitivity from the self-mixing mechanism and a good spectral resolution from the resonant response by optimizing the degree of geometrical and/or electronic symmetries.