We derive at first-order the carrier and velocity conservation equations and a pseudo-2D (P2D) Poisson equation in order to obtain an analytical model suitable for the study of the optical and electrical excitations of the plasma modes in a gated semiconductor channel of arbitrary thickness. We calculate the dispersion relation of the plasma waves appearing in the channel and the frequencies of the eigen modes for different boundary conditions (BCs). Then, we obtain and comment different THz-range frequency responses to an uniform optical beating or to an electrical excitation applied on the gate or the drain contacts. The effects of the different stimulations and boundary conditions are compared, and the responses, characterized by sharp resonances in the THz range, are interpreted as the sum of the contribution of the different hybrid plasma modes excited in the slab.

A field effect transistor can be used as a nonlinear element for the resonant detection of incident terahertz (THz) radiation at room temperature. The excitation of the plasma modes in the channel significantly increases the detection efficiency in the THz range. By means of a numerical hydrodynamic model, we study the drain-current response of a high electron mobility transistor to a THz signal applied on its gate and/or on its drain contacts to obtain the optimal configuration in terms of detection. We demonstrate that the amplitudes of the harmonic and average drain-current responses associated with the presence of plasma modes in the channel strongly depend on which transistor terminal collects the incident THz radiation and that a maximum dcresponse can be obtained by appropriately dephasing the two electrode signals.Index Terms-Field effect transistor (FET), III-V semiconductor materials, millimeter wave transistors, plasma waves, semiconductor device modeling, submillimeter wave devices.

We analyze electronic noise in field-effect transistors associated with plasma waves in the terahertz frequency domain by using a numerical approach based on the coupled hydrodynamic and Poisson equations. The current and voltage noise spectra, calculated by means of the transfer impedance method, exhibit a series of peaks associated with two- and three-dimensional plasma resonances. The two-dimensional plasma peaks have been found to depend on the channel length including gated and ungated regions. Under asymmetric boundary conditions, electrical instabilities characterized by terahertz oscillations of the drain voltage and gate current can be reached at sufficiently high values of the total drain current. A resonant enhancement of the plasma peaks in the noise spectra has been found to be a precursor of the instability onset. Through a spatial analysis of the local contributions we have shown that the main contribution to the total noise at frequencies near the plasma resonance comes from the ungated n-region placed between the source and the gate contacts.

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