Above and below threshold terahertz plasmon modes in AlGaN/GaN grating-gate HEMTs

In this work, we studied the gate voltage dependence of THz transmission spectra of AlGaN/GaN grating-gate structures consisting of two-dimensional electron gas (2DEG) covered by high active area (2x2 mm(2)) metal surface grating. Resonance absorption minima revealed in the measured THz spectra were related to 2D plasma resonances existing in the grating plasmonic structures. The high quality of the grating-gate electrode allows us to investigate the plasmon modes in the wide range of the applied gate voltages: above and far below the threshold voltage.