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A study of the small-signal response of a Field-Effect Transistor connected to a purely reactive load is proposed. In particular, this model, using the equivalent admittances approach, is applied to a transistor connected to an inductance L, a capacitance C and LC resonant and anti-resonant circuits. The influence of such frequency-dependent load on the dynamics of the transistor, dominated in the terahertz range by collective plasma behavior, is investigated. This leads to the possibilities of shifting, amplifying or softening resonances appearing in the voltage gain spectrum. The effect of a resistive part of the load is also estimated.

We investigate the shortening of the gate-length in submicrometric and nanometric field-effect transistors as a powerful tool to improve their self-oscillations performances in the terahertz frequency region due to the appearance of the Dyakonov–Shur instability. The theoretical model is based on the numerical solution of hydrodynamic equations for the electron transport in FETs/HEMTs channels. We show that a decrease of the gate length allows, on the one hand, to increase the intrinsic resonant frequencies near 1 THz and, on the other hand, to improve the conditions for the onset of the Dyakonov–Shur instability and related phenomena. The small-signal characteristics calculated under constant drain-voltage operation are compared with the drain-voltage self-oscillations calculated under constant drain-current operation.

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.

We propose an analytical approach for the admittance response calculation of the high mobility InGaAs channel transistors. The development of the small-signal admittance takes into account the longitudinal and transverse electric fields through a pseudo two-dimensional approximation of the Poisson equation. The frequency-dependent small-signal admittance response is determined by the total currents and the potentials matrix relation between the gate and the drain terminals. The analytical results show that the admittance spectrum exhibits a series of resonant peaks corresponding to the excitation of plasma waves. The appearance of the resonance is discussed as functions of the channel length and the temperature. The model can be used, on one hand, to control the appearance of plasma resonances, and on the other hand, can give a significant information about the admittance phase frequency dependence.

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.

A Monte Carlo simulation of electron transport in In0.53Ga0.47As and InAs is performed in order to extract the main kinetic parameters: mean valley population, effective mass, drift velocity, mean energy, ohmic and differential mobility. Most of these quantities are crucial for the development of macroscopic numerical models. Moreover, for some calculated quantities, analytical interpolation equations are given in order to achieve easy implementation in numerical codes. A comparison between our Monte Carlo calculation and several experimental and theoretical calculations is also carried out in order to validate the results.

Electron transport and drain current noise in wurtzite GaN MOSFETs have been studied by Monte Carlo particle simulations which simultaneously solve the Boltzmann transport and pseudo-2D Poisson equations. It is shown that at positive gate voltages giving excess electron concentration in the n-region of the channel the drain current, self-oscillations in the THz frequency range up to 5 THz are possible. These self-oscillations are driven by electron plasma instability. Moreover, a step-like drain current dependence on drain bias is demonstrated.

We propose an hydrodynamic approach for the calculation of the small-signal equivalent elements of InGaAs HEMTs. The values of the different elements are calculated from the Y parameters of the intrinsic HEMT and are obtained from the Fourier analysis of the device transient response to voltage-step perturbations at the drain and gate electrodes. For low biases and for frequencies up to 100 GHz, the values of the intrinsic elements are independent of the frequency in the whole range of device operation. However, for frequencies higher than 100 GHz, the transconductance, the conductance and the gate-drain capacity depend on frequency due to the presence of non-stationary dynamic phenomena in the HEMT channel.

International audience

Periodic arrays of nanorods can present a resonant response at specific geometric conditions. We use a multiple scattering approach to analyze the optical response of subwavelength nanowire gratings made of arbitrary anisotropic materials. When the rods are made of magneto-optical dielectrics we show that there is a complex interplay between the geometric resonances of the grating and the magneto-optical Kerr effects (MOKE) response. As we will show, for a given polarization of the incident light, a resonant magneto-optical response can be obtained by tuning the incidence angle and grating parameters to operate near the resonance condition for the opposite polarization. Our results could be important to understand and optimize MOKE structures and devices based on resonant subwavelength gratings and could open new perspectives in sensing applications. © 2014 IOP Publishing and Deutsche Physikalische Gesellschaft., This work was supported by Ikerbasque Visiting Fellowship (JJS), EU Project Nanomagma NMP3-SL-2008-214107, by LABEX WIFI (Laboratory of Excellence within the French Program 'Investments for the Future') under references ANR-10-LABX-24 and ANR-10-IDEX-0001-02 PSL*, by the Spanish Ministerio de Ciencia e Innovación through CSD2007-00046 (NanoLight.es); CSD2008-00023 (Funcoat); FIS2009-13430 ; MAT2011-29194-C02-01; FIS2012-3611 and by the Comunidad de Madrid P2009/TIC-1476., P2009/TIC-1476/MICROSERES-II

—By means of a numerical hydrodynamic (HD) modelcoupled with Poisson pseudo-2D equation , we simulate the draincurrent response of a high electron mobility transistor (HEMT)to a THz signal applied to its gate and/or to its drain contacts inorder to obtain the optimal configuration in terms of detection. I. I NTRODUCTION Study of plasma oscillation in two dimensional electronicgas (2D) channel was initiated by Dyakonov and Shur [1], [2].they showed that the nonlinear properties of the 2D plasma inthe FET channel can be used for detection of the THz emission.The resonant detection of THz radiation by two-dimensionalplasma waves was demonstrated using InAlAs/InGaAs Highelectron mobility transistor (HEMT) [4], and at room temper-atures [3]. In this paper, by simulating the High Electron Mo-bility Transistor (HEMT) drain current response, we study theplasma wave oscillation and optimise the HEMT performancesas THz detector.II. A NALYTICAL MODEL AND DISCUSSION GateSource Channel DrainBuffer/substrateV

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.

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.

We develop a perturbative formalism for the interaction of a magneto-optical nanoparticle with a flat surface made of a dielectric or metallic material. The formalism leads to a simple interpretation of the interplay between the purely dielectric and the magneto-optical responses, in terms of excitation of (and radiation by) two orthogonal electric dipoles. We analyze two different routes for the enhancement of the magneto-optical response with respect to the purely dielectric contribution, both based on the nanoparticle-surface interaction. The enhancement is discussed in terms of relevant magneto-optical signals, such as changes in reflectivity, polarization (Kerr) rotation, and ellipticity, This work was supported by the EU Project Nanomagma NMP3-SL-2008-214107

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.

We investigate the presence of plasma resonances in InGaAs n+−n−n+ diodes under different optical excitation conditions. In particular, we study the case of diodes submitted to an optical photoexcitation presenting a beating in the terahertz frequency domain. For this purpose, we calculate the electric field response in the middle of the n and n+ regions using a hydrodynamic approach self-consistently coupled to a one-dimensional Poisson solver. In particular, the analysis of the electric field response to an optical beating as a function of the doping and the geometry of the devices allows us to evidence in all the considered cases the presence of resonances in both n and n+ regions. However, while the observed resonances agree with the theoretical 3D plasma frequency in the n+ external regions, we point out a shift towards higher frequencies in the n region. We show that this shift towards the n+ 3D plasma frequency is due to the strong coupling between the two region modes, and tends to disappear when the n region lengthens, whereas the influence of the n+ regions length on the resonance frequency is negligible. Moreover, we show that the amplitude of the plasma resonances can be enhanced at high doping levels and by increasing the level of the optical photoexcitation. The obtained results show clearly that the resonances associated with 3D plasma waves in InGaAs diodes lie in the THz domain for typical values of dopings and lengths, thus opening new possibilities to exploit not only field effect transistors but also diodes as solid-state terahertz devices operating at room temperature.

A theoretical model based on simple hydrodynamic equations coupled with a pseudo-2D Poisson equation is used to calculate numerically and to analyze analitically electronic noise in FET/HEMT channels induced in the THz frequency range by the thermal excitation of 2D-plasma waves. The influence of ungated regions on high-frequency (HF) noise is considered. An efficient suppression of HF noise is found to take place in the case of additional ungated region placed between the gate and drain contacts.

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.

By Monte Carlo simulations we investigate the plasma spectrum in n -type InGaAs field effect transistors at 300 K in the whole region of operating conditions from ohmic to saturation regime of the transconductance characteristics. The presence of a two dimensional (2D) plasma peak predicted within the gradual channel approximation is confirmed by the microscopic model and its properties are analyzed systematically. At the highest gate voltages the 2D peak is found to become practically independent of the channel width.

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.

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.

By means of a Monte Carlo simulation, we have studied the collector transit region of an innovative InAs/AlSb quantum hot electron transistor constituted by a 100 nm-long InAs bulk region. This original vertical transport device has the potential to efficiently exploit the unrivalled transport properties of InAs to reach THz frequencies.

By means of a numerical hydrodynamic model, we investigate the influence of collective plasma modes in a field-effect transistor channel under different excitation and biasing conditions. Firstly, we study the case of a device externally-excited by a harmonic optical beating or an electronic excitation and current-driven operation at the drain. The harmonic and continuous responses of the drain-source bias show sharp resonances related to the first odd plasma modes, whose frequencies and amplitudes can be modified by playing on the drain bias. Secondly, we calculate the spectral density of drain voltage fluctuations in the absence of external excitations by using the generalized impedance-field method. Also the noise spectrum exhibits peaks corresponding to the excitation by the background noise of odd plasma modes.

Measurements of terahertz resonant emission due to the excitation of plasma waves by an optical beating inside AlGaAs/InGaAs/InP high electron mobility transistors are reported at 300 K and 200 K.

We investigate 3D plasma resonances in InGaAs n+ − n − n+ diodes undergoing an optical beating excitation at room temperature. For this sake, we calculate the electric field response in the middle of the diode regions by using a hydrodynamic approach coupled to a one-dimensional Poisson solver. The results show clearly the presence of three-dimensional plasma resonances in the terahertz frequency domain for the two region types. We also emphasize a strong coupling between the plasma modes. Finally, the influence of both geometry and doping profile on the amplitude and the frequency of the resonances is evaluated.

In this work, by means of Monte Carlo simulations we analyze the dependence of the DC drain current value in a 80nm-gate InAlAs/InGaAs HEMTs on the frequency of a sinusoidal signal superimposed to the DC gate bias. Interestingly, a resonant peak appears in the drain current response, which lies in the THz frequency range, in good agreement with recent experiments made on similar devices. Moreover, the frequency of the resonant peak is dependent on the length of the source-gate region, but independent of the length of the drain-gate region, thus indicating that the source-gate region acts as the plasma wave cavity leading to the resonant detection of THz radiation in HEMTs.

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.

Radiative corrections to the polarizability tensor of isotropic particles are fundamental to understand the energy balance between absorption and scattering processes. Equivalent radiative corrections for anisotropic particles are not well known. Assuming that the polarization within the particle is uniform, we derived a closed-form expression for the polarizability tensor which includes radiative corrections. In the absence of absorption, this expression of the polarizability tensor is consistent with the optical theorem. An analogous result for infinitely long cylinders was also derived. Magneto optical Kerr effects in non-absorbing nanoparticles with magneto-optical activity arise as a consequence of radiative corrections to the electrostatic polarizability tensor., This work has been supported by the EU NMP3-SL-2008-214107-Nanomagma, the Spanish MICINN Consolider NanoLight (CSD2007-00046), FIS2006-11170-C02-02 and by the Comunidad de Madrid Microseres-CM Program. R.G.-M. acknowledges support from the EU COST-MP0803. Work by R.G.-M. and L.S.F.-P. was supported by the MICINN “Juan de la Cierva” Program.

We present technological bricks and concepts under study which could permit build up of future THz remote sensing systems. Critical issues regarding such systems mainly rely on the availability of sensitive and compact detectors together with powerful and versatile sources. Potential use of plasma waves in nano-transistor is presented which can be exploited for the realization of an efficient mixer operating at THz frequencies to be implemented in a coherent detection scheme. In such a scheme the necessary local oscillator is obtained from a solid state dual frequency laser whose architecture is also detailed. On the emitter side, the preliminary realization of sub-millimeter wave to THz amplifier based an vacuum tube technology, including carbon nano-tubes is also presented.

We propose a method for the heterodyne detection of terahertz (THz) signals. The nonlinear element is constituted by the channel of an High Electron Mobility Transistor (HEMT), while the optical beating of two laser beams exciting plasma waves in the transistor channel plays the role of the THz local oscillator. We numerically show, through an hydrodynamic modelling, the efficiency of such a mixer.

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.

We investigate the presence of plasma resonances in InGaAs diodes under different optical excitation conditions. In particular, we study the case of diodes submitted to an optical photoexcitation presenting a beating in the terahertz frequency domain. The responses of the diodes are calculated using a hydrodynamic approach coupled to a one-dimensional Poisson solver. The results show clearly the presence of three-dimensional plasma resonances in the terahertz frequency domain. We also show that the resonances frequency and amplitude can be tuned by modifying the diode geometry and doping profile.

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.

We investigate the influence of collective plasma modes in a field-effect transistor channel under different excitations and biasing conditions. First, we study the case of a device externally-excited by a harmonic optical beating or an electronic excitation and current-driven at the drain. The harmonic and continuous responses of the transistor are calculated using a pseudo-two-dimensional hydrodynamic approach. They show sharp resonances related to the first odd plasma modes, whose frequencies and amplitudes can be modified by playing on the drain bias. Then, through the generalized impedance-field method we calculate also the spectral density of drain voltage fluctuations in the absence of external excitations. Also these noise spectra exhibit peaks corresponding to the odd plasma modes.

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.

International audience; A photomixed laser beam of two 1.55 μm lasers is used to obtain interband photoexcitation at the difference frequency and at room temperature in suvmicron gate length INAIA/InGaAs transistors. Results show the clear excitation of plasma oscillation modes in the transistors channel Fundamental plasma resonant frequency and its add harmonics can be tuned with the applied gate voltage. Numerical simulation have also been performed using a hydrodynamic approach coupled to a pseudo-2D Poisson equation. Numerical results are in qualitative agreement with experiments and confirm optical beatin detection at terahertz frequencies.

Electron transport and drain current noise in wurtzite GaN MOSFET have been studied by Monte Carlo particle simulation that simultaneously solves the Boltzmann transport and pseudo-2D Poisson equations. It is shown that at positive gate voltages giving excess electron concentration in the n-region of the channel, drain current self-oscillations in the THz frequency range up to 6 THz are possible. These self-oscillations are driven by an electron plasma instability. Additionally a step-like drain current dependence on drain bias is demonstrated.

We present an analytical model based on hydrodynamic equations and a pseudo-two-dimensional Poisson equation to study the response of a nanometric field-effect transistor channel in the THz domain. This model allows to study different kinds of external excitations of plasma modes and different geometries. We calculate the two first-order responses of the drain voltage or current, which are of peculiar interest in the perspective of THz wave generation and detection and THz electronics. Even at room temperature, each responses present resonances at the eigenfrequencies of the hybrid plasma modes sustained in the channel.

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.

We simulate electron transport in ultra small mercury-cadmium-telluride n+-n-n+ diodes using a hydrodynamic approach. A numerical staggered solution is employed to treat the coupled hydrodynamic and Poisson equations, where the spatial profiles of the main transport parameters within the diodes are analyzed including the Auger generation-recombination processes. Our numerical results show that, even for low applied voltages, impact ionization processes are activated and affect dramatically the current-voltage characteristics of the Hg0.8Cd0.2Te diode.

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

By means of Monte Carlo simulations coupled with a two-dimensional Poisson solver, we evaluate directly the possibility to use high mobility materials in ultra fast devices exploiting ballistic transport. To this purpose, we have calculated specific physical quantities such as the transit time, the transit velocity, the free flight time and the mean free path as functions of applied voltage in InAs channels with different lengths, from 2000 nm down to 50 nm. In this way the transition from diffusive to ballistic transport is carefully described. We remark a high value of the mean transit velocity with a maximum of 14×105 m/s for a 50 nm-long channel and a transit time shorter than 0.1 ps, corresponding to a cutoff frequency in the terahertz domain. The percentage of ballistic electrons and the number of scatterings as functions of distance are also reported, showing the strong influence of quasi-ballistic transport in the shorter channels.

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.

An as yet unexploited Magneto Optical Kerr Effect (MOKE) at evanescent distance from a surface is introduced. In the case of a magnetic particle-metallic surface system, an extraordinary intensity is discovered and fully explained by the excitation of Surface Plasmon Polariton.