Hydrodynamic study of electronic, optical and thermal excitation of plasma waves in HEMTs

By means of a numerical hydrodynamic model, we investigate the influence of collective plasma modes in a field-effect transistor channel under different excitation and biasing conditions. Firstly, we study the case of a device externally-excited by a harmonic optical beating or an electronic excitation and current-driven operation at the drain. The harmonic and continuous responses of the drain-source bias show sharp resonances related to the first odd plasma modes, whose frequencies and amplitudes can be modified by playing on the drain bias. Secondly, we calculate the spectral density of drain voltage fluctuations in the absence of external excitations by using the generalized impedance-field method. Also the noise spectrum exhibits peaks corresponding to the excitation by the background noise of odd plasma modes.