Search

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.

The classical impedance field method is one of the most powerful techniques to calculate electronic noise in semiconductor structures. This method fails when applied to deep submicron devices due to the presence of spatial correlations between noise sources. To overcome this drawback, a new technique (generalised impedance field) has been developed in the frame of a hydrodynamic simulator. Analogously to the classical method, the calculation of electronic noise requires the knowledge of two quantities: the local noise sources and the generalised impedance fields. Instead of using a hydrodynamic approach to obtain the generalised impedance fields and a Monte Carlo simulation for the noise sources, we have used a microscopic simulator (the Scattered Packet Method) to compute both quantities.

We survey recent results on electronic noise in nanostructured devices. Three kinds of excess noise referring to hot-carriers in submicron n+nn+ diodes, shot noise in mesoscopic structures, resistance fluctuations in thin film conductors, are considered. The influence of down-sizing on fluctuations is illustrated in each case.

High electron-mobility transistors can be used as efficient detectors of an incident THz radiation on its metallic electrodes. This detection can become strongly resonant if the frequency of the THz radiation coincides with plasma eigenfrequencies of the transistor channel. By using a hydrodynamic model we investigate in parallel the transistor intrinsic high-frequency current noise spectrum and its harmonic and average current responses to a voltage perturbation at the electrodes. In both cases we discuss the appearance of resonances associated with the excitation of 2D and 3D plasma modes and, to get an additional physical insight into the properties of the different parts of the transistor, we compute also the local noise spectra originated by electron velocity perturbations distributed in the channel. We demonstrate that the main resonances in the drain current noise spectrum are the same as those observed in the current response to an external THz excitation thus confirming the strong link existing between these two quantities.

In this contribution we propose an analytical approach for the calculation of the high-frequency noise spectrum of frequency multipliers based on n+n-metal Schottky-barrier diodes and n+n - barrier - nn+ Heterostructure-barrier varactors. The model includes a diodes operating in series with a parallel resonant circuit to extract the harmonics generated in the terahertz frequency region.

In this paper we propose an analytical model for the calculation of the spectral density of current fluctuations in Heterostructure-barrier varactors . The structures of the calculated spectra are analyzed in terms of physical processes useful to optimize the device parameters for the extraction of the high-order harmonics.

We present a theoretical analysis of the thermal conductivity of charge carriers in semiconductors under nonequilibrium conditions due to an applied electric field. The theory is based on a correlation-function formalism which directly relates this kinetic coefficient to four spectral densities involving carrier velocity and energy flux fluctuations. Monte Carlo calculations performed for the cases of p-Si and n-GaAs give an evidence of a strong dependence of the thermal conductivity on increasing electric fields.

An analytical model for the noise spectrum of nanometric Schottky-barrier diodes (SBD) is developed. The calculated frequency dependence of the spectral density of current fluctuations exhibits resonances in the terahertz domain which are discussed and analyzed as functions of the length of the diode, free carrier concentration, length of the depletion region and applied voltage. A good agreement obtained with direct Monte Carlo simulations of GaAs SBDs operating from barrier-limited to flat-band conditions fully validates the proposed approach.

We investigate the possibility to suppress the diffusion noise in semiconductor bulk materials by adding to the constant electric field a fluctuating contribution characterized by a gaussian distribution and a characteristic time. The general theory is applied to the specific cases of Si and GaAs and investigated by Monte Carlo simulations. Numerical results confirm the possibility to suppress the intrinsic noise and the best conditions to realize this effect are analyzed in detail.

We investigate the possibility to suppress the diffusion noise in bulk semiconductors by adding to a constant electric field a fluctuating contribution characterized by a gaussian distribution and a characteristic time. To this purpose, Monte Carlo simulations are performed applied to the case of GaAs at room temperature. Numerical results confirm the possibility to suppress the total noise power by an appropriate choice of the externally added noise.

This paper overviews and implements the transfer-field method applied to the calculation of electronic noise in small semiconductor structures. Two basic schemes are used and developed in detail. The former considers velocity fluctuations and the latter acceleration fluctuations as microcopic noise sources. We show that the latter scheme has several advantages with respect to the former one. Indeed, starting from Markovian noise sources, the latter scheme separates the time and spatial evolution of the local noise sources. In this way, the dual representation of the noise spectral density in terms of impedance and admittance fields is recovered. A remarkable achievement is that from the knowledge of the bulk Langevin sources at a hydrodynamic level it is possible to calculate the noise spectra of non-homogeneous structures even for nanometric devices. The method is validated by comparing the results of the present scheme with those obtained from self-consistent Monte Carlo approaches for different structures of interest.

One of the most suitable techniques to compute noise in electronic devices is the standard impedance field method, a deterministic approach able to provide analytical and numerical solutions for the noise spectra of electronic devices at a hydrodynamic (HD) level. The starting point of our investigation consists in showing that this method is not appropriate for the calculation of noise spectra in deep submicron devices where spatial correlations between noise sources are of relevant importance. To overcome the difficulties which are intrinsic to the standard impedance field method we have developed a new scheme based on Langevin forces and generalized transfer fields.

International audience

We present an analytical modeling of the noise temperature associated with velocity fluctuations obtained in the framework of the linear‐response theory around a steady state. The expressions are rigorously related to an eigenvalue expansion of the response matrix and are applicable to ohmic as well as to nonohmic (hot‐carrier) conditions. Theory requires as input parameters the reciprocal carrier effective mass, the drift velocity, the carrier energy, the variance of velocity fluctuations, and the covariance of velocity‐energy fluctuations as functions of the electric field in stationary and homogeneous conditions. The analytical results obtained for the case of holes in Si and electrons in GaAs at T=300 K are validated by comparison with experiments.

We present analytical expressions for the differential‐mobility spectra which are obtained from a linear analysis of the balance equations under stationary and homogeneous conditions. The expressions are rigorously related to an eigenvalue expansion of the response matrix and are applicable to ohmic as well as to non‐ohmic conditions. The coefficients appearing in the formula can be calculated from the knowledge of three parameters as functions of the electric field, namely, the reciprocal effective mass, the drift velocity, and the average energy of the carriers. The theory is applied to the case of holes in Si at T=300 K and validated by comparison with the results obtained by a direct numerical resolution of the perturbed Boltzmann equation.