Investigation of high-frequency small-signal characteristics of FETs/HEMTs

Hydrodynamic calculations of the components of small-signal admittance and impedance matrix are performed for InGaAs HEMT. Modifications of high-frequency small-signal response spectra in going (i) from ungated to gated structures and (ii) from a thermally equilibrium state without a stream to a nonequilibrium state with the stream of carriers in the FET/HEMT channel are considered. The main attention is paid to the spectral behaviour of the admittance and impedance in the THz frequency range related to the excitation of 2D and 3D plasma oscillations in the gated and ungated regions of the conducting channel of FET/HEMT, respectively. Accompanied effects related to plasma phenomena such as the competition of 2D and 3D plasma oscillations, amplification of 3D and Dyakonov–Shur instability of 2D plasma oscillations and resonant detection of external THz action are discussed.