J. Pousset

Hydrodynamic modeling of optically excited terahertz plasma oscillations in nanometric field effect transistors

We present a hydrodynamic model to simulate the excitation by optical beating of plasma waves in nanometric field effect transistors. The biasing conditions are whatever possible from Ohmic to saturation conditions. The model provides a direct calculation of the time-dependent voltage response of the transistors, which can be separated into an average and a harmonic component. These quantities are interpreted by generalizing the concepts of plasma transit time and wave increment to the case of nonuniform channels. The possibilities to tune and to optimize the plasma resonance at room temperature by varying the drain voltage are demonstrated.

Monte Carlo investigation of terahertz plasma oscillations in ultrathin layers of n-type In0.53Ga0.47As

By numerical simulations we investigate the dispersion of the plasma frequency in a n-type In0.53Ga0.47As layer of thickness W and submicron length at T=300K. For W=100nm and carrier concentrations of 1016–1018cm−3 the results are in good agreement with the standard three-dimensional (3D) expression of the plasma frequency. For W⩽10nm the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency values are in good agreement with the two-dimensional (2D) expression of the plasma frequency obtained for a ballistic regime within the in-plane approximation for the electric field. A region of cross over between the 2D and 3D behaviors of the plasma frequency is evidenced for W>10nm.

Monte Carlo investigation of terahertz plasma oscillations in gated ultrathin channel of n-InGaAs

By numerical simulations we investigate the dispersion of the plasma frequency in a gated channel of n-type InGaAs layer of thickness W and submicron length L at T=300 K. In the presence of a source-drain voltage and for a carrier concentrations of 1018 cm−3 the spectra evidences a peaked shape with two main bumps, the former at high frequency corresponding to the three-dimensional plasma frequency and the latter at a low frequency. The frequency value of the latter peak exhibits a dispersion as the inverse of the channel length in agreement with the predictions of gradual channel approximation. At increasing drain voltages the instabilities associated with the presence of Gunn domains are responsible for a suppression of the plasma peak in favor of the onset of a peak in the subterahertz domain associated with transit time effects.

A Monte Carlo investigation of plasmonic noise in nanometric n-In0.53Ga0.47As channels

By means of numerical simulations we investigate the plasma frequency associated with voltage fluctuations in an n-type In0.53Ga0.47As layer of thickness W and submicron length L embedded in a dielectric medium at T = 300 K. For W = 100 nm and carrier concentrations of 1016–1018 cm−3 the results are in good agreement with the standard three-dimensional (3D) expression for the plasma frequency. For W≤10 nm the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency values are in good agreement with the two-dimensional (2D) expression for the plasma frequency obtained for a collisionless regime within the in-plane approximation for the self-consistent electric field. A region of crossover between the 2D and 3D behaviours of the plasma frequency, which we address as an open problem, is evidenced for W>10 nm. Problems associated with channel lengths shorter than the electron mean free path and the effects of an applied bias will be discussed.

Plasmonic noise in silicon nanolayers

We report a microscopic investigation of the spectrum of voltage fluctuations in nanometric n-Si layers. Theory makes use of a Monte Carlo simulator self-consistently coupled with a two-dimensional Poisson solver. We consider layers of variable thickness W in the range of 2–100 nm and variable length L in the range of 10–1000 nm embedded in an external dielectric medium. Calculations are performed at T=300 K for different doping levels and in the presence of an applied voltage of increasing strength. The spectra are found to exhibit peaks centered on the terahertz region. For W≥100 nm and carrier densities of 5×1017 and 5×1018 cm−3, the frequency peaks agree with the value of the three dimensional plasma frequency. For W≤100 nm, the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency covers a wide range of values of 0.2–10 THz and is in agreement with the values of the two-dimensional plasma frequency predicted by existin...

Noise analysis of plasma wave oscillations in InGaAs channels

Nanometric InGaAs‐based High Electron Mobility Transistors (HEMTs) have been shown experimentally to generate and detect THz radiation. The observed phenomena can be attributed to the presence of plasma waves inside the transistor channel. To investigate these oscillations we have performed Monte Carlo simulations of InGaAs homogeneous channels of different length and thickness. To detect the presence of plasma waves we have calculated the spectral density of voltage fluctuations under thermodynamic equilibrium at 300 K. Results confirm the presence of 3D and 2D plasma modes according to the topology of the channel.

Modified hydrodynamic approach for the modeling of high‐frequency noise in FETs

We present a modified hydrodynamic approach to simulate high frequency noise in field‐effect transistors. The model is based on the coupling of standard 1D hydrodynamic equations for carrier concentration, velocity and energy with a modified pseudo‐2D Poisson equation. The advantage of this approach lies in the possibility to take into account the effect of a gate within a simple 1D approach. The model is applied to the case of GaAs FETs at room temperature and validated through the calculation of the small‐signal admittance and of the spectral density of current fluctuations in the framework of the generalized admittance field method.