J. P. Nougier

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 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...

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.

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.

Transfer impedance calculations of electronic noise in two-terminal semiconductor 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.

Field‐dependent conductivity of lightly doped p‐Si at 77 K

A theoretical investigation and new experiments on the conductivity of lightly doped p‐Si (boron) at 77 K are presented. The conductivity is studied as a function of the electric field in the range 10<E<104 V/cm. The experimental results are interpreted within an original Monto Carlo simulation which includes the mechanism of generation and recombination from impurity centers, thus allowing a simultaneous calculation of the mobility and the fraction of ionized impurities. The good agreement between the theory and the experiments supports the reliability of the physical model suggested.

Electronic noise of submicron n+nn+ diodes under near‐oscillatory macroscopic behaviors

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.

Impedance field and noise of submicrometer n+ nn+ diodes: analytical approach

A theoretical model for the noise properties of n+nn+ diodes in the drift-diffusion framework is presented. In contrast with previous approaches, our model incorporates both the drift and diffusive parts of the current under inhomogeneous and hot-carrier conditions. Closed analytical expressions describing the transport and noise characteristics of submicrometer n+nn+ diodes, in which the diode base (n part) and the contacts (n+ parts) are coupled in a self-consistent way, are obtained.

A MODEL HYPERFREQUENCY DIFFERENTIAL-MOBILITY FOR NONLINEAR TRANSPORT IN SEMICONDUCTORS

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.