J. C. Vaissiere

Determination of transient regime of hot carriers in semiconductors, using the relaxation time approximations

It is shown that in a semiconductor, where impurity and polar optical phonon scatterings are not involved, the transient velocity is the solution of a relaxation time equation. Relaxation times can be defined as functions of the stationary energy, thus leading to relaxation time equations which are good approximations for describing the transient average energy and drift velocity. Comparisons between the relaxation time description, and the transient response obtained by iterative or Monte Carlo methods, are performed on p‐Ge and n‐Si, and show an agreement better than 10% in a wide range of electric fields and lattice temperatures.It is shown that in a semiconductor, where impurity and polar optical phonon scatterings are not involved, the transient velocity is the solution of a relaxation time equation. Relaxation times can be defined as functions of the stationary energy, thus leading to relaxation time equations which are good approximations for describing the transient average energy and drift velocity. Comparisons between the relaxation time description, and the transient response obtained by iterative or Monte Carlo methods, are performed on p‐Ge and n‐Si, and show an agreement better than 10% in a wide range of electric fields and lattice temperatures.

Monte Carlo simulation of the generation of terahertz radiation in GaN

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...

Monte Carlo calculation of noise and small‐signal impedance spectra in submicrometer GaAs n+nn+ diodes

The time‐and‐frequency behavior of hot‐carrier noise in submicrometer n+nn+ GaAs diodes is investigated theoretically using the Monte Carlo method. We have continuously investigated the noise from current‐to‐voltage operation mode by calculating the noise‐power spectrum at the terminals of a noiseless load‐resistance R connected in series with the diode. By varying appropriately the value of R we have calculated the small‐signal impedance of the diode and then obtained the full spectrum of the noise temperature. Under voltage‐operation mode the current–noise spectrum exhibits two resonant peaks at the transit‐time and plasma frequencies, respectively. Under current operation mode, all current oscillations are effectively damped, and the voltage–noise spectrum exhibits a quasi‐Lorentzian shape, which vanishes at the transit‐time frequency. The behavior of hot‐carrier noise closely parallels the frequency dependence of the diode small‐signal impedance, which exhibits a dynamic negative differential resistan...

Monte Carlo calculation of electronic noise under high-order harmonic generation

The 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.

Langevin forces and generalized transfer fields for noise modeling in deep submicron devices

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.

Matrix determination of the stationary solution of the Boltzmann equation for hot carriers in semiconductors

The stationary Boltzmann equation is solved by using a matrix method. This allows determining directly the steady state regime for hot carriers in semiconductors. The main advantages of this new method are: the result does not depend on initial conditions, and the cost is much lower than that of iterative or Monte Carlo techniques, particularly at high electric field.

Monte Carlo simulation of Schottky diodes operating under terahertz cyclostationary conditions

We report Monte Carlo simulations of the current response and noise spectrum in heavily doped nanometric GaAs Schottky-barrier diodes (SBDs) operating under periodic large-signal conditions in the forward bias region. Due to the rather thin depletion region and heavy doping of these diodes, we find that the returning carrier resonance is shifted well above the terahertz region, so that the low-frequency noise plateau extends over the terahertz region. Here, frequency multiplication and mixing can take place at noise levels equal or below than that of full shot noise. We show that the signal-to-noise ratio of these SBDs is definitely superior to that of bulk semiconductors exploiting velocity-field nonlinearity.

On the diffusivity of holes in silicon

The longitudinal diffusion coefficient of holes in Si has been measured with time‐of‐flight and noise techniques at 300 K for field strengths ranging from about 0.5 up to 40 kV/cm. As the electric field increases, the diffusion coefficient decreases to about 0.3 of its Ohmic value much more sharply than results previously reported in literature. The experimental results are interpreted by a Monte Carlo simulation which includes warping and nonparabolicity effects of the heavy‐hole band.

Noise sources of hot carriers in space‐charge regimes

The noise term involved in the impedence field method, for modelling the noise of devices, which may work under both space‐charge and hot carrier conditions, is shown to be proportional to the local noise temperature and to the local ac conductivity. This allows one to determine the noise source term experimentally, which is performed, as an example, for n‐type silicon at 77 K. Also are established the mathematical conditions, under which the impedance field method reduces to the salami method.

Analytical model of high-frequency noise spectrum in Schottky-barrier diodes

We propose an analytical model for the high-frequency noise of Schottky-barrier diodes (SBD). The high-frequency spectrum is shown to be governed by collective motions of carriers in the neutral region of the SBD caused by the self-consistent electric field. The model is validated by comparison with Monte Carlo simulations of GaAs SBDs operating from barrier-limited to flatband conditions.