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A hypothesis on the possible occurrence of the superplasticity phenomenon in local zones of friction contact is put forwarded. An extended classification of friction junctions is developed with consideration for the superplasticity phenomenon. A relation for the coefficient of friction which considers the possibility of the occurrence of the superplasticity phenomenon over a portion of the friction surface is obtained.

One- and two-step syntheses of composite coatings with an A–OOO polyimide matrix filled with 40-nm tungsten disulfide nanoparticles produced using gas-phase synthesis, which are intended for operation under dry friction conditions, are described. Results of studying the tribological behavior of these coatings are presented.

A synthesis is described and tribological characteristics are presented for composite coatings 40 μm thick with a PM–DADPE polyimide matrix and a filler of tungsten disulfide nanoparticles with size of 4 nm and tungsten diselenide nanoparticles 60 × 5 nm in size obtained via gas-phase synthesis.

Electron transport and drain current noise in optimized for THz generation wurtzite GaN MOSFET have been studied by Monte Carlo particle simulation which simultaneously solve the Boltzmann transport and pseudo-2D Poisson equations. The drain current and average electron energy under the gate at 300 K is calculated as a function of drain bias. The electron cooling when average electron energy under the gate is less than thermal electron energy is demonstrated. The step like current voltage relation due to the optical phonon emission is shown. It is found that THz generation in frequency range from 6 to 10 THz is possible at room temperature.

Electron transport and drain current noise in the wurtzite GaN MOSFET have been studied by Monte Carlo particle simulation which simultaneously solves the Boltzmann transport and pseudo-2D Poisson equations. A proper design of GaN MOSFET n+nn+ channel with uncentered gate in n-region 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 at 300 K is maximal in frequency range from 0.5 to 7 THz. At higher frequenciea the detection current rapidly decreases due to the inertia of electron motion.

We present a theoretical investigation of high-frequency electronic noise in field-effect transistors used as detectors of TeraHertz radiation. Calculations are performed using the hydrodynamic-Langevin approach and specialized to the case of InGaAs high-electron mobility transistors. The main physical phenomena associated with the effect of branching of the total current between channel and gate and the appearance of two-dimensional plasma waves are discussed. We demonstrate that thermally excited standing plasma waves originate series of resonant peaks in the corresponding noise spectral densities whose presence can be controlled by the embedding circuit. A significant damping of the high-frequency excess noise is found when the transistor is submitted to a two-lasers optical photo-excitation presenting a beating frequency in the TeraHertz range. Finally, we discuss the dependence of the damping effect, as well as a shift of the resonance peaks from the presence of channel ungated regions.

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.

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.

The problems related with the intrinsic noise in FET/HEMT channels induced by continuous branching of the total current between channel and gate are considered in the framework of a simple analytical model and its predictions on the current-noise spectra. Main branching-induced effects such as the appearance of an additional noise related to the excitation of plasma waves, its dependence on FET/HEMT embedding circuits, interference properties, etc. are analysed.

Possibilities and advantages of the electro-optical sampling (EDS) technique for the investigation of excitation of THz-range 2D plasma waves in FET/HEMT channels are considered both experimentally and theoretically. It is experimentally demonstrated that the EOS technique allows one to identify an excitation of 2D plasma waves in the HEMT channel under a given working point determined by external embedding circuits. Theoretical simulations show that the development of the instability of 2D plasma waves can be easily identified in the framework of the EOS technique.

We investigate by means of Monte Carlo simulations the physical processes associated with the emission of TeraHertz radiation in different electronic devices. We analyze four alternative and complementary strategies which seem to be promising candidates to obtain the TeraHertz emission: (1) a nitride maser based on the optical-phonon transit-time resonance, (2) the high–order harmonic generation in bulk materials and nanometric Schottky-barrier diodes, (3) the excitation of coherent plasma oscillations in micron and submicron diodes, (4) the current instabilities and plasma oscillations in high electron mobility transistors (HEMT). The numerical results show that several physical mechanisms can be exploited to increase significantly the operating frequency of these devices and the best conditions to optimize the radiation emission in the TeraHertz range are studied in detail.

International audience; The low-field mobility spectrum and related quantities is calculated for a nonparabolic band by using the exact solution of the linearized Boltzmann transport equation within the relaxation time approach. Numerical calculations are applied to bulk nitrides at different lattice temperatures and impurity concentrations.

To qualify the feasibility of standard semiconductor materials and Schottky‐barrier diodes (SBDs) for THz high‐order harmonic generation and extraction, the harmonic intensity, intrinsic noise and signal‐to‐noise ratio are calculated by the Monte Carlo method when a periodic high‐frequency large‐amplitude external signal is applied to a semiconductor device. Due to very high signal‐to‐noise ratio heavily doped GaAs SBDs are found to exhibit conditions for frequency mixing and harmonic extraction that are definitively superior to those of bulk materials. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The conditions for THz radiation generation caused by electron transit-time resonance in momentum and real spaces under optical phonon emission are analyzed for nitride-based materials and their structures. It is shown that such a mechanism provides a unique possibility to realize sub-THz and THz radiation generation at the border between the electro-optical and electronic techniques by using two alternative approaches: (i) amplification of transverse electromagnetic waves in 3D bulk materials and 2D quantum wells, and (ii) longitudinal current-field instabilities in sub-micron and micron n(+)nn(+) diodes. Estimations of frequency regions, output power and efficiency of the generation demonstrate that nitrides are promising materials for THz radiation generation.

We present an analytical model suitable for the study of the plasma modes in gated semiconductor slabs of arbitrary thickness. A pseudo-two-dimensional Poisson equation allows us to consider both transverse and longitudinal electric field variations. We calculate the dispersion relation demonstrating the dispersive nature of the slab. We express the frequencies of the plasma modes appearing in a cavity. A transition from a two-dimensional to a three-dimensional behavior is revealed when the transverse dimension of the device or the order of modes grow. These analytical results show a good agreement with Monte Carlo calculations of the voltage noise spectrum.

Electron transport in InN n+nn+ diodes is investigated by the Monte Carlo Particle technique at temperatures below about 80 K, when optical phonon emission is the dominating scattering mechanism. It is shown that at constant bias, high enough to force strong electron optical phonon interaction but below the threshold value for intervalley transfer processes, the profiles of the relevant physical quantities exhibit a periodic spatial behaviour in the n-region, thus leading to the formation of a superlattice like structure. Such a structure is found to be responsible for microwave power generation in the THz frequency range.

International audience; The feasibility of bulk semiconductors subjected to strong periodic electric fields for terahertz radiation generation due to the high-order harmonic extraction is analyzed by using Monte Carlo simulations. The high-order harmonic intensity and the spectral density of velocity fluctuations are calculated for GaAs, InP, and InN. By comparing the harmonic intensity with the noise level the threshold bandwidth for high-order harmonic extraction determined by their ratio is introduced and evaluated for the above materials. The results show that semiconductor materials with a high value of the threshold field for the Gunn-effect are characterized by a high value of the threshold bandwidth under high-order harmonic generation and, hence, they are promising materials for microwave generation in the THz frequency range by high-order harmonic extraction.

International audience

The conditions for microwave power generation under the quasi-periodic motion of carriers caused by the combined action of carrier acceleration in a constant electric field and optical phonon emission at low temperatures are analysed by means of Monte Carlo simulations of both small- and large-signal responses in bulk nitrides such as GaN and InN. It is shown that, as a consequence of the high value of the optical phonon energy and the strong electron-phonon interaction, a dynamic negative differential mobility caused by transit-time resonance occurs over a wide frequency range which covers practically the whole submillimetre range and persists in the THz frequency range up to liquid nitrogen temperature. The efficiency of the amplification and generation is found to depend nonmonotonically on: (i) the static and microwave electric field amplitudes, (ii) the generation frequency, and (iii) the carrier concentration. Accordingly, for each generation frequency there exists an optimal range of parameter values. Under optimal conditions we predict a generation efficiency of about 1-2% in the 0.5-1.5 THz frequency range.

The conditions for microwave power generation at low temperatures under optical phonon emission are analyzed by Monte Carlo simulations of both small- and large-signal responses in bulk zinc blende and wurtzite GaN. As a result of the high optical phonon energy and the strong interaction of electrons with optical phonons in GaN a general improvement on the transit-time resonance and a considerable increase in the maximum generation frequency and power can be achieved in comparison to the widely studied III–V materials such as GaAs and InP. A dynamic negative differential mobility caused by transit-time resonance occurs in a wide frequency range of about 0.05–3 THz and persists in the THz frequency range up to the liquid nitrogen temperature with doping levels up to about 5×1016 cm−3. The efficiency of the amplification and generation is found to depend nonmonotonously on static and microwave electric field amplitudes, generation frequency, and doping level so that for each generation frequency there exist...

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.

The aim of this work is to calculate the amplification band and the maximum gain for an optical phonon transit-time resonance (OPTTR) maser based on bulk zincblende and wurtzite GaN. For this sake the response function of the longitudinal velocity in the time domain representation is obtained by an extended averaging over the before- and after-scattering ensembles during Monte Carlo simulations. Then the differential mobility spectrum is calculated by Fourier transformation. In the frequency region of dynamic negative differential mobility (DNDM), the gain is determined and we investigate its dependence on frequency, applied electric field, lattice temperature, and doping level.

A universal description of the OPTTR-assisted generation band of THz radiation is developed in the framework of a 3D transport in bulk materials and 2D transport in QWs and HLs. On the one hand, in the framework of an ideal streaming motion we have carried out an analytical investigation based on phonon scattering rates: namely, elastic deformation acoustic phonons in the passive energy region below the optical-phonon energy 0 and emission of polar optical phonons in the active energy region, 0. On the another hand, quantitative estimations of the qualitative constraints given by Eqs. 1 and 2 for the streaming conditions are obtained on the basis of numerical calculations of the OPTTR DNDM by the Monte Carlo method. It is found that i for Eq. 1 the average momentum relaxation time in the passive region must satisfy the condition −1–2E and ii for Eq. 2 carrier penetration into the active region must occurr at a level less than 14%–15%. In the framework of such a model we have provided simple analytical expressions that estimate the low- and high-frequency limits of the generation band determined by, respectively, the average relaxation time − see Eq. 25 and the carrier penetration into the active region see Eq. 33. Having in mind that for THz radiation generation the high-frequency limit is of the most interest, for the highfrequency cutoff of the DNDM we have found that i for 3D bulk materials the relevant physical quantities are the carrier effective mass, the optical-phonon energy, and the polaroptical coupling strength; ii in passing from 3D to 2D vertical transport, for the same material the influence of 2D transport on the OPTTR is characterized entirely by the dimensionless parameter k0d related to both the radius of the optical-phonon sphere in wave-vector space k0 and the effective width of the electron localization d associated with the lowest miniband of the QW/HL structure; iii in going from 3D to 2D transport, the change of the energy dependence of the density of states is responsible for an extension of the maximum generation frequency for up to a factor of 5 times. In essence, such a model gives the “upper” estimation of the generation band limits determined primarily by the parameters of a bulk material and a 2D structure. Any other scatterings not incorporated directly into our model— namely, impurity, electron-electron, interface roughness, etc.—act mainly on the low-frequency limit since one can speak about the upper limit only in the case when an electron runaway from the regime of low-energy scatterings in the passive region takes place. Of course, the presence of additional low-energy scatterings will increase the low-frequency limit and eventually destroy the generation. Nevertheless, additional scattering mechanisms can be simply incorporated into the model by taking into account their contribution to the average momentum relaxation time in the passive region − as 1/−=1/DA+1/imp +1/ee. For example, such a procedure was used to estimate − in the experimental observation of the OPTTR generation in bulk InP.20 These estimations give relaxation times, which is reasonably close to the values estimated above.

International audience; The conditions for THz radiation generation caused by electron transite-time resonance in momentum and real spaces under low-temperature optical-phonon emission are analysed. Main attention is paid to transverse electromagnetic waves generation in: (i) 3D bulk materials and (ii) 2D quantum heterosctructures as well as (iii) longitudinal current instabilities in submicron and overmicron n+nn+ diodes. It is found that in all the cases considered the nitride-based materials and structures are the most preferable for the THz radiation generation as compared with III-V compounds. Furthermore, a considerable increase up to 5 times of the high-frequency cutoff for THz radiation generation is predicted in going from 3D to 2D transport.

International audience; We report Monte Carlo simulations of electronic noise in heavily doped nanometric GaAs Schottky-barrier diodes (SBDs) recently proposed as promising devices for THz applications. We consider a SBD operating in series with a parallel output resonant circuit when a high-frequency large-signal voltage is applied to the whole system. Significant modifications of the noise spectrum with respect to the diode subjected to a constant applied voltage are found to occur in the THz-region. To interpret such behaviour, we have developed a simple analytical approach based on the static I-V and C-V relations as well as on the series resistance of the SBD

International audience

We review recent results concerning the microscopic analysis of electronic noise in semiconductor unipolar structures in the frequency range where 1/f noise can be neglected. Calculations are based on a Monte Carlo simulator of the carrier motion self-consistently coupled with a Poisson solver. Both current- and voltage-noise operation modes are considered and their respective advantages illustrated. The analysis is applied to structures with increasing degree of complexity, that is: homogeneous materials, resistors, n+ nn+ diodes., Schottky-barrier diodes and GaAs MESFETs. The main sources of noise like diffusion, generation-recombination, coupling between velocity and local electric field fluctuations, etc. are treated in the presence of electric fields of arbitrary strength. Results should constitute the basis for a physical interpretation of electronic noise in most semiconductor materials and devices thus providing inputs for improving quality and reliability figures of merit.

The noise temperature of GaAs ${\mathit{n}}^{+}$${\mathit{nn}}^{+}$ two-terminal structures of micrometer and submicrometer lengths is theoretically analyzed as a function of frequency and applied voltage. Calculations are performed at a kinetic level, and are based on a mixed Monte Carlo hydrodynamic scheme. Different operation modes of the structure are considered, namely, when operating as a nonlinear resistor (passive device) as well as when operating as a Gunn amplifier or generator (active device). Under generating conditions the noise temperature at low frequency is found to go to infinity for voltages above the threshold value for the Gunn effect, as expected in bulk material. Under amplifying conditions the noise temperature at low frequency is found to remain finite even at applied voltages well above the threshold value for the Gunn effect. At high frequencies the noise-temperature spectrum shows structures associated with transit-time effects, carrier energy, and plasma-time effects. In particular, we calculate the noise figure of merit covering both amplifying and passive conditions. Very good agreement is found between theory and available experiments. \textcopyright{} 1996 The American Physical Society.

A hydrodynamic approach based on velocity and energy conservation equations is developed and used for the simultaneous evaluation of the electronic steady-state transport, small-signal response and noise in an Si structure. An original decomposition of velocity and energy profiles along the structure in terms of field, convective and diffusion contributions is presented. The local distribution of the noise source and voltage spectral density is carried out within the transfer-impedance method. The excellent agreement of the approach thus developed with Monte Carlo simulations supports its physical reliability and effectiveness for submicron-device modelling.

An analytical model of the high-frequency noise of frequency multipliers based on Schottky-barrier diodes (SBD) operating in series with a parallel resonant circuit under large-signal conditions is developed. Such a model, on one hand, takes into account the main intrinsic features of the SBD noise related to shot-noise, returning carriers, plasma resonance at n+n homojunctions, and, on the other hand, it incorporates the SBD noise spectrum modifications induced by the output resonant circuit. It is shown that the SBD embedding into an external circuit can produce the appearance of an extra noise due to up-down conversion of the fluctuations of the voltage drop between the SBD terminals originated by a periodic modulation of the varactor capacitance by the pumping signal.

International audience; We report on photo-induced terahertz radiation with a high spectral purity generated by a submicron sized InGaAs-based high-electron-mobility transistor. The emission peak is due to the electron-hole pairs photocreated in the transistor channel at the frequency of the beating of two cw- laser sources. The radiation frequency corresponds to the lowest fundamental plasma mode in the gated region of the transistor channel. The observed high emission quality factor at 200K is interpreted as a result of stream-plasma instability in the two-dimensional electron gas whose appearance is emphasized by the reduction of the velocity relaxation rate with the temperature.

A closed hydrodynamic model and the associated numerical procedures are developed for simulating hot‐carrier transport in submicron semiconductor devices. To check the validity of the model, the steady‐state characteristics of near‐micron n+nn+ InP diodes are compared with a standard Monte Carlo approach. The excellent agreement found fully validates the physical reliability of our model which has been further developed to investigate linear and nonlinear time‐dependent characteristics. The contribution of each part of the device, when operating as microwave power‐generation, is analyzed through the spatial profiles of the impedance‐field spectrum. The usual subdivision of the n‐region into a passive (dead‐zone) and active zone is carried out. The dead zone is found to manifest itself as a purely real resistance which is practically independent of the frequency. One or more spatial zones which are responsible for the generation are shown to be formed in the active region of the diode. By reducing the leng...

We present a joint analytical and numerical study of plasmonic noise in gated semiconductor slabs of arbitrary thickness. Through the analysis of the high-frequency spectral density of voltage fluctuations we show that the positions of the frequency resonances depend on the topology of the slabs. A transition from a 2D to a 3D behavior is revealed when the channel length decreases or when the order of the modes grows. In particular, the resonance frequencies converge towards the value of the 3D plasma frequency which represents the maximum possible value for resonance frequencies.

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.

By means of a numerical hydrodynamic model, we consider the mechanism of collective plasma oscillations in a field-effect transistor channel under different excitations and biasing conditions. First, we consider the case of a device externally-excited by a harmonic optical beating or an electronic excitation under constant current condition at the drain. Both situations exhibit sharp resonances related to the first odd plasma modes illustrating the possibility of using the HEMT as a terahertz photomixer or detector. Then, we demonstrate that the frequencies, amplitudes and quality factors of the resonances can be strongly modified by varying the drain biasing condition from currentto voltage-driven operation.

Results of hydrodynamic simulation of HEMT performance under photo‐mixing excitation of free carriers in the conducting channel are presented. A resonant enhancement of current amplitudes at the beating frequency due to excitation of 2D plasma waves is demonstrated.

A modified Poisson equation able to take into account the influence of gates and a ?-doping in FETs and HEMTs is proposed. This equation can be solved self-consistently together with 1D transport equations along inhomogeneous transistor channels like those of the hydrodynamic or drift-diffusion approximations or with a Monte Carlo simulator used to describe carrier transport in n+nn+ structures.

A method for the heterodyne detection of terahertz (THz) signals is proposed. A high electron mobility transistor is used as a nonlinear element, while the optical beating of two laser beams exciting plasma waves in the transistor channel plays the role of the THz local oscillator. High efficiency and room-temperature operation of such a mixer are demonstrated by numerical simulations.

The transmission spectra at 300, 77, and 7 K of GaN quantum wells using a 220–325 GHz electronic source are investigated. Enhanced signals in the transmission spectra — interpreted as preliminary indications of the activation of the OPTTR mechanism — are obtained when a bias voltage is applied to the device. Results can be considered as a relevant step in the development of devices capable to produce THz radiations.

We report on systematic measurements of resonant plasma waves oscillations in several gate-length InGaAs high electron mobility transistors (HEMTs) and compare them with numerical results from a specially developed model. A great concern of experiments has been to ensure that HEMTs were not subject to any spurious electronic oscillation that may interfere with the desired plasma-wave spectroscopy excited via a terahertz optical beating. The influence of geometrical HEMTs parameters as well as biasing conditions is then explored extensively owing to many different devices. Plasma resonances up to the terahertz are observed. A numerical approach, based on hydrodynamic equations coupled to a pseudo-two-dimensional Poisson solver, has been developed and is shown to render accurately from experiments. Using a combination of experimental results and numerical simulations all at once, a comprehensive spectroscopy of plasma waves in HEMTs is provided with a deep insight into the physical processes that are involved.

The spatio‐temporal evolution of Gunn and Ryzhii current instabilities and accompanied noise behavior in n+nn+ structures is investigated by the Monte Carlo particle technique. It is found that the transition from a passive‐state to a generation‐state is accompanied by an anomalous giant enhancement of the noise at frequencies quite lower than those corresponding to generation. By comparing various transport and noise features it is demonstrated that such a giant enhancement of low‐frequency noise can be considered as an indicator for the onset of a high‐frequency instability.

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 investigate the noise behavior in the presence of current instabilities induced by optical phonon emission. Calculations are carried out by means of Monte Carlo particle simulations of InP n+nn+ diodes at lattice temperatures below about 80 K. A giant enhancement of the low-frequency noise is observed in a narrow voltage region, which precedes the onset of current self-oscillations caused by the instability. A possible origin of this enhancement is discussed. The impact of the non-linear effects on the anomalous low-frequency noise behavior is stressed.

In the framework of analytical and hydrodynamic models for the description of carrier transport and noise in high electron mobility transistor/field-effect transistor channels the main features of the intrinsic noise of transistors are investigated under continuous branching of the current between channel and gate. It is shown that the current-noise and voltage-noise spectra at the transistor terminals contain an excess noise related to thermal excitation of plasma wave modes in the dielectric layer between the channel and gate. It is found that the set of modes of excited plasma waves can be governed by the external embedding circuits, thus violating a universal description of noise in terms of Norton and Thevenin noise generators.

A Monte Carlo simulation of electron transport in mercury–cadmium–telluride is performed in order to extract the most important material kinetic parameters such as electron drift velocity, mean energy, effective mass, differential mobility, diffusion coefficient, impact ionization rate, velocity and energy relaxation rates. Most of these quantities are necessary for the developments of macroscopic numerical models. Moreover, for the calculated quantities, analytical interpolation formula are given in order to achieve easy implementation in numerical codes. The main results demonstrate that hot-electron transport and impact ionization processes occur for relatively weak electric fields, that is around 100 V/cm. The high mobility of mercury–cadmium–telluride, which makes it a good material for fast applications, is verified. Finally, a comparison between the Monte Carlo calculations, hydrodynamic simulations and experimental data is made for both stationary and transient regimes, which validates the results.

We present a hydrodynamic-Langevin scheme to describe electronic noise in unipolar structures and evaluate the cross-correlation functions of conduction current fluctuations entering the transfer impedance method. The theory is developed in terms of microscopic fluctuations of carrier velocity and energy taking place during scattering events. Applications to submicron n+nn+ GaAs structures show that the contribution of stochastic velocity rate prevails over that of the energy rate in determining the cross-correlation function of conduction current fluctuations.

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.

International audience; A photomixed laser beam of two 1.55 mum continuous-wave lasers is used for interband photoexcitation in submicron gate length InAlAs/InGaAs transistors. Results show the clear excitation of plasma oscillation modes in the transistor channel. A strong amplification of the optical beating detection in the 0-600 GHz range is observed as a function of drain-source voltage. Numerical results, using hydrodynamic model coupled to a pseudo-2D Poisson equation, are in good agreement with experiments concerning the plasma frequency dependence with gate voltage. Moreover, this model confirms both optical beating detection at subterahertz frequencies and the enhancement observed when drain-source voltage increases.

We show that within the transfer impedance method, the spectral strength of the local noise source originally defined by Van Vliet et al. [J. Appl. Phys. 46, 1804 (1975)] should be more generally replaced by the two-point spectral density of current fluctuations. The theoretical arguments are further supported by numerical results for the voltage noise spectrum associated with conduction–current fluctuations in submicron n+nn+ structures. The above two-point spectral strength is, in general, a complex quantity related to fluctuations induced by velocity fluctuations only.