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A closed hydrodynamic approach based on the system of conservation equations for carrier number, drift velocity and mean energy coupled with the Poisson equation is used to calculate the response functions in the time domain of the local electric field and applied voltage for a near-micrometre n+nn+ InP diode. By Fourier analysis, the generation bands in the frequency domain are then obtained. The good agreement achieved with available experiments validates the present theoretical approach. A significant increase of the cut-off frequency of the microwave power generation up to 600-700 GHz is predicted for submicrometre GaAs and InP diodes.

International audience; The high-frequency generation associated with the optical-phonon transit-time resonance in a constant electric field is analyzed by Monte Carlo simulations of different nitrides such as InN, GaN and AlN. Calculations show that the microwave power generation occurs in a wide frequency range covering practically the whole submillimeter range and persisting in the THz frequency range up to the liquid nitrogen temperature.

International audience; he time and frequency behavior of hot-carrier velocity fluctuations in bulk semiconductors subjected to strong periodic electric fields is analyzed by using two complementary approaches based on the correlation function and the finite Fourier transform. Monte Carlo calculations performed for GaAs, InP, and InN show that semiconductor materials with a high value of the threshold field for the Gunn effect are characterized by a high value of the signal-to-noise ratio under high-order harmonics generation and, hence, they are promising materials for microwave generation in the terahertz frequency range by high-order harmonic extraction.

We present Monte Carlo calculations of electronic noise in bulk materials and submicron semiconductor structures subject to periodic electric fields or voltage/current excitations of high frequency and large amplitude. The modifications of the noise spectra with respect to the static case are analyzed. Under appropriate conditions the noise spectra exhibit a resonant peak which is interpreted as upconversion of hot‐carrier intergroup noise.

In the attempt to derive the regression theorem from the fluctuation dissipation theorem several authors claim the violation of the former theorem in the quantum case. Here we pose the question: does it exists a quantum fluctuation dissipation theorem (QFDT) in its conventional interpretation? It is shown that the relation usually called as the QFDT is the condition of detailed macroscopic energetic balance. Following this interpretation the existing conflict between the two theorems in the quantum case is removed., Comment: 13 pages, 3rd Int. Conf. on Unsolved Problems on Noise (will be published in Proceedings)

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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.

We present a theoretical investigation on the electrical behavior of submicrometer n+nn+ diode microwave generators. To this end we adopt a mixed scheme which uses space‐homogeneous and stationary Monte Carlo simulations to provide the input parameters for a hydrodynamic analysis of the diode performances. Comparison between GaAs and InP made devices working at 400 K give similar results by predicting generation frequencies up to 700 GHz for an active region length of 0.2 μm.

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We show that the standard impedance field method that considers as noise source the spectral density of velocity fluctuations is not appropriate for the calculation of noise spectra in deep submicron devices where spatial correlations between velocity fluctuations cannot be neglected. To overcome this drawback, we develop a new scheme in which the noise sources are given by the instantaneous accelerations of relevant dynamic variables caused by scattering events. Accordingly, generalized transfer fields describing the propagation of fluctuations to the device terminals are introduced. By using this scheme, we show that, in contrast with the standard impedance field method, noise modeling in submicron structures can be performed with no major difficulty and the dual representation of voltage and current noise is recovered.

The article presents a critical discussion on the evaluation of the impedance field for noise analysis by means of several transport models. The models considered are the drift-diffusion model, the full hydrodynamic model, and the scattered packet method for the direct solution of the Boltzmann transport equation. The comparison is carried out on a canonical Si p+pp+ diode at ambient temperature. The agreement found between the approaches is good, thus suggesting that the evaluation of the impedance field does not require any additional care with respect to other, more conventional operating conditions.

We present a unifying scheme for the hydrodynamic calculation of electronic noise in semiconductor devices operating under various conditions. In the framework of the Green-function formalism the noise sources corresponding to the Langevin forces originated by single scattering events are included into the equations describing medium properties. The scheme is validated by numerical calculations of the voltage and current noise in submicron n + nn + GaAs structures.

The time-domain formulation of the transfer-impedance method is developed to calculate the impedance field of two-terminal semiconductor structures. The voltage noise spectrum associated with velocity fluctuations is then calculated for overmicron and submicron n+nn+ GaAs diodes in the framework of a closed hydrodynamic approach based on the velocity and energy conservation equations. Transit-time effects are found to influence substantially the noise spectrum in a wide frequency range above 10 GHz. The good agreement found with Monte Carlo simulations validates the proposed theoretical approach.

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An GaAs structure is proposed for microwave power generation in the terahertz frequency region. The structure allows one both to realize within a mean free path distance a quasi-ballistic beam of hot electrons moving through a cold plasma and to use intervalley transfer to upper valleys as a strong mechanism for beam modulation. Kinetic energy is thus transferred from hot electrons to coherent plasma oscillations. The main features of such a generator are investigated by the Monte Carlo particle simulation.

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.

Temporal and spatial modulation of light-induced free carrier plasma and its heating by applied electric field lead to novel effects in transport phenomena, which may be used for various purposes such as contactless techniques for measurements of kinetic coefficients and nonequilibrium carrier dynamics, high-speed optoelectronics, holography, etc. Combining light diffraction on light-induced free carrier (FC) transient grating (TG) with an electron gas heating by uniform microwave (MW) field in GaAs, we estimated hot carrier diffusion coefficients and their field dependencies1. Hot carrier transport and non-linear optical phenomena which arise in TG due to non-uniform carrier heating are not sufficiently studied.

We present a theoretical investigation on the electronic noise of submicron n+nn+ GaAs diode under the conditions when the electrical characteristics of the diode exhibit a pronounced near‐oscillatory macroscopic behavior caused by velocity fluctuations of single particles at the microscopic level. Two kinds of spontaneous oscillations, related to transit time and plasma oscillations, and their contributions to the diode noise are investigated by a Monte Carlo simulation. A simple analytical model which provides an excellent fit of the macroscopic features of the noise obtained by the Monte Carlo simulation is developed.

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.

Within an ensemble Monte Carlo method, we simulate a bipolar transport in a vertical layered n-GaAs/n-AlGaAs/i-GaAs heterostructure placed between n + and p + contacts. A very fast switching time and, hence, a very high frequency (up to 1 THz) of the voltage oscillations are predicted.

The transfer impedance method in the time-domain formulation is applied to calculate the impedance field of submicron n + nn + GaAs diodes in the framework of a closed hydrodynamic approach. The method enables us to determine the voltage noise-spectrum associated with velocity-fluctuations. The good agreement found with Monte Carlo simulations validates the proposed theoretical approach.

The quantum fluctuation dissipation theorem (QFDT) in the Callen–Welton [ Phys. Rev.83 (1951) 34] form is critically revisited. We show that the role of the system eigenvalues is in general not correctly accounted for by the accepted form of the QFDT. As a consequence, a series of quantum results claimed in the literature, like the presence of zero point fluctuations, the violation of the quantum regression hypothesis, the non-white spectrum of the Langevin force, etc. emerge as a consequence of an incorrect application of the theorem. In this context the case of the single harmonic oscillator is illustrated as a typical example where the accepted form of the QFDT is proven to fail.

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.

We investigate the electronic noise and impedance field of submicron n+nn+ diode generators when loaded by an external resistance in the framework of a Monte Carlo and a hydrodynamic simulative approach. We observe a long-time oscillation of the correlation function of the voltage drop fluctuations between the resistor terminals. The oscillations are in turn responsible for a peak in the noise power-spectrum which is caused by the spontaneous formation of electron accumulation layers. The drift of these layers through the n-region is monitored for biasing conditions above threshold for microwave generation. The frequency of the noise peak is shown to correspond to the highest generation frequency for the given load resistance. The noise power-spectra calculated for three different values of the load resistance are used to obtain the small-signal and noise characteristics of the intrinsic unloaded diode. The parallel hydrodynamic calculation of the diode impedance spectrum is found to compare well with the results obtained from the noise analysis of the Monte Carlo simulation.

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We report on measurements of radiation transmission in the 0.220–0.325 THz frequency range through GaN quantum wells grown on sapphire substrates at nitrogen and room temperatures. Significant enhancement of the transmitted beam intensity with applied voltage is found at nitrogen temperature. This effect is explained by changes in the mobility of two-dimensional electrons under electric bias. We have clarified which physical mechanism modifies the electron mobility and we suggest that the effect of voltage-controlled sub-terahertz transmission can be used for the development of electro-optic modulators operating in the sub-THz frequency range.

High frequency (350 to 750 GHz) generation in submicron InP diodes is investigated by modified hydrodynamic (MH) and Monte Carlo particle (MCP) techniques. The noise power spectral density Pn in the diode loaded by resistor R and generation spectra Pg in series resonant LR circuit are calculated by MCP technique. It is shown that at the biases above the generation threshold the Pn has a peak at the frequency fmax which corresponds to the highest generation frequency at the given R. The excess noise arise in the frequency region where the real part of diode impedance has negative values. The Pg broadening at high frequencies is the result of interaction between the self‐oscillation at frequency fmax and LR circuit driven oscillations.

By using a closed hydrodynamic model coupled with the field impedance method we evaluate the small‐signal and noise spectra of submillimeter n+nn+ diode generators. Calculations performed for the case of InP with applied fields near the switching on of self‐oscillations evidence a sharp peak of the current spectral‐density at the generation frequency.

The current voltage characteristics and the spectra of the: small-signal response, current self-oscillations, and microwave power generation are analyzed by means of a theoretical simulation of near micron InP diodes. To this purpose, both the hydrodynamic and Monte Carlo approaches are used and compared. Good agreement with available experimental data is obtained.

We develop a closed hydrodynamic model within the framework of the single-electron gas approach. Calculations are presented for the small-signal response, diffusion coefficient, spectral density of velocity fluctuations of bulk semiconductors as well as for the concentration, velocity, energy and electric-field profiles of n + nn + structures. The validation of the present model is confirmed by a favourable comparison with analogous Monte Carlo simulations.

We present continuous-wave terahertz spectroscopic results obtained with a photomixing emitter and a bolometric detection. The tested elements are candidates for a further cryogenic THz experiment which will consist to demonstrate the effective amplification by optical phonon transit time resonance in gallium nitride quantum wells.

One-dimensional approach for simulation of multi-gate FETs and HEMTS is proposed and validated by comparison with full two-dimensional simulations.

A proper profile of nonuniform doping of GaAs n+ nn+ structure to reach the maximum detection sensitivity is proposed. It is shown that the main role in formation of longitudinal transport asymmetry and THz radiation detection is played by optical phonon emission process. It is found that the detection current independs of frequency in spectral range 0.02–1 THz, reaches maximum near 2.2 THz (10 and 80 K) or 3 THz (300 K) and then becomes to decrease due to the inertia of optical phonon emission process.

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.

We review recent investigations of nonlinear carrier transport and related optical nonlinearities in GaAs and InP crystals for the case in which photoexcited carriers are nonuniformly heated by a strong external electric field and are redistributed in a spatially nonuniform internal electric field. We simulated the nonequilibrium carrier and internal field spatial evolution in picosecond and nanosecond time domains and estimated criteria for bipolar high-field Gunn-domain grating formation in dc and ac fields. The coexisting refractive-index modulation mechanisms for free-carrier and electro-optic nonlinearities are analyzed for various external field strengths, grating periods, and excitation levels, thus providing conditions for an efficient and fast electro-optic refractive-index modulation by the transient Gunn-domain grating. Comparison of the experimentally observed enhancement of light’s self-diffraction efficiency with numerical calculations has confirmed that the nonresonant electro-optic Gunn-domain-based nonlinearity may exceed the free-carrier nonlinearity.

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