Terahertz Emission in an Asymmetric Dual-Grating-Gate High-Electron Mobility Transistor Plasmonic Photomixer under dc Current Flow

We report on terahertz (THz) emission from a current-driven asymmetric dual-grating-gate high-electron-mobility transistor (ADGG-HEMT) excited by photomixed dual-CW-infrared laser irradiation whose difference frequency $(\delta f)$ was set around the THz plasmon-mode frequencies of the 2D electrons in the channel. The radiation spectra observed at 100 K showed two distinctive emission components beyond the black-body radiation, one promoted by $\delta f$ independent thermally excited incoherent plasmons and the other promoted by $\delta f$ dependent coherent plasmons. The results suggest the occurrence of the plasmonic instability stimulated by the dc current flow in the channel.