Terahertz plasmons in grating-gate AlGaN/GaN HEMTs

Plasma excitations in high-electron mobility transistors (HEMTs) with two-dimensional (2D) electron channels can be used for detection, mixing, and generation of terahertz (THz) radiation. Plasmon modes excited in the HEMT channel under the gate contact (gated plasmons) were considered to be more attractive for electronic applications because their frequencies can be effectively tuned by varying the gate voltage. However, the gated plasmons are difficult to couple to THz radiation due to acoustical nature and, hence, a small net dipole moment of this plasmon mode. Hence, special antenna elements are needed to couple the gated plasmons to THz radiation. As an alternative, a grating gate in a large area (comparable with a typical cross-section area of THz beam) HEMT structure can act as an aerial matched antenna strongly coupling the plasmons to THz radiation. It was shown recently that a large-area grating-gate GaAs/AlGaAs structure can operate as an electrically tunable detector in sub-THz frequency range. A double-grating-gate HEMT structure with lateral dimensions smaller than THz wavelength was used as an effective THz photomixer and emitter.