ABSTRACT We present a modified hydrodynamic approach to simulate high frequency noise in field-ef... more ABSTRACT We present a modified hydrodynamic approach to simulate high frequency noise in field-effect transistors. The model is based on the coupling of standard 1D hydrodynamic equations for carrier concentration, velocity and energy with a modified pseudo-2D Poisson equation. The advantage of this approach lies in the possibility to take into account the effect of a gate within a simple 1D approach. The model is applied to the case of GaAs FETs at room temperature and validated through the calculation of the small-signal admittance and of the spectral density of current fluctuations in the framework of the generalized admittance field method.
ABSTRACT We present two original methods which yield the small-signal response around the dc bias... more ABSTRACT We present two original methods which yield the small-signal response around the dc bias in bulk semiconductors, using direct numerical resolutions of the perturbed Boltzmann equation. The first method operates in the frequency domain. An ac sinusoidal electric-field perturbation superimposed to the dc field produces an ac perturbation of the distribution function which is computed at each frequency. The second method operates in the time domain. A step electric-field perturbation is superimposed at time t=0 to the dc field. The resulting perturbations of the distribution function and of the average velocity are then computed as functions of time. These methods are applied to the case of holes in silicon at T=300 K under hot-carrier conditions and are used to compute the perturbed distribution function and the differential mobility spectrum.
When reducing the dimensions of a device, carrier transport goes from diffusive to ballistic regi... more When reducing the dimensions of a device, carrier transport goes from diffusive to ballistic regime and both current-voltage characteristics and Johnson-Nyquist noise caused by carrier scattering processes acquire new features. In diffusive regime the characteristic scattering processes are spatially isotropic, the current autocorrelation functions exhibit a standard exponential behavior and, therefore, the spectral densities of current fluctuations are Lorentzians. In ballistic regime the transport is mostly determined by transit times, which are either between the contacts or between the boundaries, and the associated scattering processes are spatially anisotropic depending on the sample geometry. In this regime, the current autocorrelation functions become non-exponential giving rise to: a redistribution of the noise at higher frequencies (blue-shift), a deviation of the noise spectrum from the Lor-entzian shape and, in particular cases, a series of geometrical resonances in the spectrum.1–5
35th International Conference on Infrared, Millimeter, and Terahertz Waves, 2010
By means of a Monte Carlo simulation, we have studied the collector transit region of an innovati... more 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.
2013 22nd International Conference on Noise and Fluctuations (ICNF), 2013
ABSTRACT The possibility to develop a novel technique that might provide a direct measurement of ... more ABSTRACT The possibility to develop a novel technique that might provide a direct measurement of the impedance field using an electromagnetic near-field equipment is investigated. Preliminary experiments have been performed on silicon substrate using a coaxial near-field probe. The first results show a signal transmission via an air coupling and not a propagation inside the device. Some critical problems have been identified to improve the test-bench.
A theoretical investigation and experiments on the noise spectra of lightly doped p-type Si (boro... more A theoretical investigation and experiments on the noise spectra of lightly doped p-type Si (boron) at 77 K are presented. Noise spectra in the high-frequency range 0.22<=f<=10.5 GHz have been measured at different electric fields 100<=E<=2500 V/cm for two acceptor concentrations NA of 4×1014 and 3×1015 cm-3. The experimental results are interpreted within a Monte Carlo simulation, which includes at
ABSTRACT By using the Monte Carlo method, submicron Si n+nn+ structures are analysed at different... more ABSTRACT By using the Monte Carlo method, submicron Si n+nn+ structures are analysed at different bias voltages and lengths of the n region. The autocorrelation function of current fluctuations and the variance of carrier number in different parts of the device is used to investigate the correlations induced by the self-consistent solution of the Boltzmann and Poisson equations and the influence of the modelling of the contacts.
Within a correlation-function (CF) formalism we present a theoretical analysis of the Kelvin-Onsa... more Within a correlation-function (CF) formalism we present a theoretical analysis of the Kelvin-Onsager coefficients (KOC) relating generalized fluxes to the applied external forces for a carrier system in a one-dimensional ballistic structure. We consider a two terminal device with length l terminated by ideal contacts and investigate the transition from equilibrium to non-equilibrium conditions. The basis of the kinetic description
ABSTRACT We present a modified hydrodynamic approach to simulate high frequency noise in field-ef... more ABSTRACT We present a modified hydrodynamic approach to simulate high frequency noise in field-effect transistors. The model is based on the coupling of standard 1D hydrodynamic equations for carrier concentration, velocity and energy with a modified pseudo-2D Poisson equation. The advantage of this approach lies in the possibility to take into account the effect of a gate within a simple 1D approach. The model is applied to the case of GaAs FETs at room temperature and validated through the calculation of the small-signal admittance and of the spectral density of current fluctuations in the framework of the generalized admittance field method.
ABSTRACT We present two original methods which yield the small-signal response around the dc bias... more ABSTRACT We present two original methods which yield the small-signal response around the dc bias in bulk semiconductors, using direct numerical resolutions of the perturbed Boltzmann equation. The first method operates in the frequency domain. An ac sinusoidal electric-field perturbation superimposed to the dc field produces an ac perturbation of the distribution function which is computed at each frequency. The second method operates in the time domain. A step electric-field perturbation is superimposed at time t=0 to the dc field. The resulting perturbations of the distribution function and of the average velocity are then computed as functions of time. These methods are applied to the case of holes in silicon at T=300 K under hot-carrier conditions and are used to compute the perturbed distribution function and the differential mobility spectrum.
When reducing the dimensions of a device, carrier transport goes from diffusive to ballistic regi... more When reducing the dimensions of a device, carrier transport goes from diffusive to ballistic regime and both current-voltage characteristics and Johnson-Nyquist noise caused by carrier scattering processes acquire new features. In diffusive regime the characteristic scattering processes are spatially isotropic, the current autocorrelation functions exhibit a standard exponential behavior and, therefore, the spectral densities of current fluctuations are Lorentzians. In ballistic regime the transport is mostly determined by transit times, which are either between the contacts or between the boundaries, and the associated scattering processes are spatially anisotropic depending on the sample geometry. In this regime, the current autocorrelation functions become non-exponential giving rise to: a redistribution of the noise at higher frequencies (blue-shift), a deviation of the noise spectrum from the Lor-entzian shape and, in particular cases, a series of geometrical resonances in the spectrum.1–5
35th International Conference on Infrared, Millimeter, and Terahertz Waves, 2010
By means of a Monte Carlo simulation, we have studied the collector transit region of an innovati... more 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.
2013 22nd International Conference on Noise and Fluctuations (ICNF), 2013
ABSTRACT The possibility to develop a novel technique that might provide a direct measurement of ... more ABSTRACT The possibility to develop a novel technique that might provide a direct measurement of the impedance field using an electromagnetic near-field equipment is investigated. Preliminary experiments have been performed on silicon substrate using a coaxial near-field probe. The first results show a signal transmission via an air coupling and not a propagation inside the device. Some critical problems have been identified to improve the test-bench.
A theoretical investigation and experiments on the noise spectra of lightly doped p-type Si (boro... more A theoretical investigation and experiments on the noise spectra of lightly doped p-type Si (boron) at 77 K are presented. Noise spectra in the high-frequency range 0.22<=f<=10.5 GHz have been measured at different electric fields 100<=E<=2500 V/cm for two acceptor concentrations NA of 4×1014 and 3×1015 cm-3. The experimental results are interpreted within a Monte Carlo simulation, which includes at
ABSTRACT By using the Monte Carlo method, submicron Si n+nn+ structures are analysed at different... more ABSTRACT By using the Monte Carlo method, submicron Si n+nn+ structures are analysed at different bias voltages and lengths of the n region. The autocorrelation function of current fluctuations and the variance of carrier number in different parts of the device is used to investigate the correlations induced by the self-consistent solution of the Boltzmann and Poisson equations and the influence of the modelling of the contacts.
Within a correlation-function (CF) formalism we present a theoretical analysis of the Kelvin-Onsa... more Within a correlation-function (CF) formalism we present a theoretical analysis of the Kelvin-Onsager coefficients (KOC) relating generalized fluxes to the applied external forces for a carrier system in a one-dimensional ballistic structure. We consider a two terminal device with length l terminated by ideal contacts and investigate the transition from equilibrium to non-equilibrium conditions. The basis of the kinetic description
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Papers by L. Varani