Quasi-neutral Layer Research Articles

Using particle simulations for parameter tuning of dynamical models of the magnetotail

WINDMI is a family of dynamical models of the magnetotail that use different closure schemes to derive truncated descriptions of the collisionless microscopic energy transfer processes occurring in the quasineutral layer. The six-dimensional systems are both Kirchhoffian and Hamiltonian in structure, ensuring that the power input from the solar wind is divided into physically realizable energy sub-components. Model parameters are defined analytically as volume integrals of physically identifiable quantities. Particle simulations are used to calculate the parameters for the various models, giving a direct comparison of the relative advantages of different closure schemes. A collisionless kinetic closure scheme that includes the heat flux gives better agreement with observations by allowing for a rapid non-adiabatic cooling of the central plasma sheet (CPS).

Near-wall layer of a positive dust–electron plasma in the presence of a nonequilibrium charging process

Accounting for a nonequilibrium charging process in a positive dust–electron plasma, a theory is developed for a quasi-neutral layer separating the near-wall space–charge sheath from the bulk plasma where the charging of the dust grains is quasi-equilibrium (i.e., the current of the electrons emitted by a dust grain is approximately equal to the current of the electrons collected by the grain). The problem is solvable when the velocity of the dust particles entering the layer from the quasi-equilibrium plasma satisfies an inequality which is mathematically, although not physically, similar to the Bohm criterion. The obtained results explain the reason for the absence of a continuous transition from the Bohm criterion in a dusty plasma with a variable dust particle charge to the conventional Bohm criterion for an electron–ion plasma with constant ion charge.

Magnetospheric dynamics from a low-dimensional nonlinear dynamics model

A physics based model for the coupled solar WIND–Magnetosphere–Ionosphere system (WINDMI) is described. The model is based on truncated descriptions of the collisionless microscopic energy transfer processes occurring in the quasineutral layer, and includes a thermal flux limit neglected in the Magnetohydrodynamic (MHD) closure of the moment equations. All dynamically relevant parameters of the model can be computed analytically. The system is both Kirchhoffian and Hamiltonian, ensuring that the power input from the solar wind is divided into physically realizable energy sub-components, a property not shared by data-based filters. The model provides a consistent mathematical formalism in which different models of the solar wind driver, ionospheric dissipation, global field configuration, and substorm trigger mechanism can be inserted, and the coupling between the different parts of the system investigated.

Well supply voltage effect on escape current of guard rings in epitaxial CMOS technology

An n-well guard ring dual collector structure formed on an epitaxial substrate has been characterized and simulated. The measured I– V characteristics have exhibited that a reduction of well supply voltage from 5.0 to 1.0 V causes an increase in the escape current into the outer well by a factor of about 14, while the base and inner guard ring collector currents are hardly changed. This will influence neighboring latchup susceptibility substantially. This experimental observation can provide a new evidence of the published theory responsible for the escape current: the injected minority carriers flow through a quasi-neutral layer between the upper collecting plate and the bottom high/low junction reflecting plate. Based on this theory actual epitaxial layer thickness can be extracted with low guard ring voltages as well.

Non-quasi-static modeling of neutral region a.c. photo currents in integrated photodiode detectors

The functional dependence of the magnitude of a.c. photo currents arising in charge neutral regions of silicon integrated photodiode detectors is studied by way of numerical small signal analysis. The analysis shows for typical integrated structures, which are compatible with standard bipolar transistor technology, that a significant portion of the a.c. photo current is generated within the surface and buried quasi-neutral layers and must be taken into account for complete a.c. characterization of the diode. A simple non-quasi-static expression is developed which is shown by comparison with a.c. numerical simulation to accurately model the response of the photo current from neutral regions to light signal modulation frequency.

Non-quasi-static models including all injection levels and DC, AC, and transient emitter crowding in bipolar transistors

Two-dimensional equivalent-circuit models for bipolar junction transistors are systematically derived by solving the continuity equations for DC, AC, and transient excitations. These models take into account carrier propagation delay, all injection levels, as well as exponential doping profiles. They include analytically DC, AC, and transient emitter crowding in a more detailed and accurate manner than previously available. Extensions of the models to accommodate arbitrarily doped and heavily doped quasi-neutral layers and to include energy-gap narrowing due to the electron-hole plasma present at high current density are described. The analysis leads to compact large- and small-signal equivalent-circuit lumped models, suitable for use in circuit simulators such as SPICE. The analytical solutions obtained reveal the two-dimensional distribution of the current and carrier densities in the intrinsic base layer and the onset of emitter crowding. They also provide information for the extraction of the intrinsic base resistance. Several assumptions made in the derivations are assessed by the computer program PISCES. The methods presented apply to both homojunction and heterojunction bipolar transistors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comments, with reply, on "One-dimensional non-quasi-static models for arbitrarily and heavily doped quasi-neutral layers in bipolar transistors" by B. Wu and F. Lindholm

For original paper see ibid., vol.36, pp.727-37 (April 1989). The accuracy of state-of-the-art AC models for the emitter and base of bipolar transistors is examined in order to clear up some confusion that the commenter believes results from original paper concerning the distinctions between a base transport model and that of J. Seitchik et al. (see IEDM Tech. Dig., pp.244-7, 1987). The authors respond with further discussion of emitter-transport and base-transport models and concede that they may have made mistakes in their comparison with the results of Seitchik et al. >

Anomalously fast charge collection in partially depleted p +n −n + silicon detectors for alpha-particle absorption through the high-low junction

A new mechanism of excess charge transport from quasi-neutral silicon is proposed to account for the fast collection of charges generated in the field-free region of partially depleted p +n −n + detectors. The new mechanism is based on the action of the n − junction and satisfactorily explains the small ballistic deficits observed from field-free layers of ca 100 μm across. The literature on field-free transport is critically reviewed. Field funnelling into the main space-charge layer of alpha-generated charge is probably important in quasi-neutral layers less than 50μm across.

Analytical determination of the emitter saturation current in ultra-shallow silicon junctions

Simple analytical relations expressing the influence of electric field strength E prevailing in the heavily-doped quasi-neutral layer of ultra-shallow (x j = 01 to 0.3 μm) silicon junctions on the emitter component of the reverse saturation current density J 0 are obtained. It is shown physically and is demonstrated mathematically that, owing to the peculiarities of such junctions, an additional field-based current term appears in the Shockley relation for the emitter component of the saturation current. For the usual values of drift velocities encountered in the heavily-doped layer of ultra-shallow junctions, the field-based term enhances substantially the emitter component of the saturation current. The particular forms of the analytical expression obtained for different practical cases of interest are detailed. The electric-field-free case is also investigated, and simple analytical expressions for emitter saturation current are derived as a function of practical values of the surface recombination vel...

One-dimensional all injection nonquasi-static models for arbitrarily doped quasi-neutral layers in bipolar junction transistors including plasma-induced energy-gap narrowing

Nonquasi-static circuit models accounting for carrier propagation delay in quasi-neutral layers are presented for bipolar junction transistors operating at all injection levels. The models are analytically derived from the Shockley equations for low injection and high injection and are empirically fitted for moderate injection. Large majority current flow in the base, which includes the case of low common-emitter current gain, is also taken into account. The models accommodate all doping profiles via a piecewise-exponential fitting scheme. For very high injection, the resulting electron-hole plasma reduces the energy gap, and this effect is also included. In the simulation of transient or frequency responses, the models provide better accuracy than does the conventional Gummel-Poon (GP) model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

One-dimensional non-quasi-static models for arbitrarily and heavily doped quasi-neutral layers in bipolar transistors

A systematic method is presented for deriving non-quasi-static equivalent-circuit models for arbitrarily doped and heavily doped quasi-neutral layers in bipolar transistors. The large-and small-signal models developed improve various aspects of the one-dimensional Gummel-Poon model for transient and frequency circuit simulation. The improvements are assessed by computer simulation and by experiment. In the simulation of high-speed or high-frequency bipolar integrated circuits, the models show advantages over the conventional Gummel-Poon model. It is shown that non-quasi-static effects are significant in the emitter as well as the base layer. The method is developed for homojunction bipolar transistors but in principle applies also to heterojunction bipolar transistors. >

Dynamics of a Thunderstorm Outflow

Abstract The kinematic and thermodynamic structures of a thunderstorm outflow are examined by means of dual Doppler radar analysis, mesonet, lower, and sounding data. The data were collected in the Denver, Colorado area during June 1984. The dual-Doppler analysis shows that the cold outflow is ducted beneath the PBL inversion. Along the gust front there is a narrow quasi-two-dimensional updraft. Kelvin-Helmholtz instability (KHI) developed along the top of the gust front head near the surface front, and propagated backwards, dissipating in the wake of the head region. An isothermal layer aloft appears to have limited billow amplification to the quasi-neutral layer below. The gust front's leading edge had numerous inflections which are believed to result from barotrophic instabilities. Small vortices develop at some of the inflection points. Detailed analysis of one such circulation shows evidence of the formation of two enhanced updrafts separated by an occlusion downdraft. These observations are the firs...

Reflection of ion-acoustic waves from an ion sheath at a grid

The reflection of continuous sinusoidal waves from a grid is investigated experimentally. It is found that the reflection coefficient has a distinct maximum in contrast to the prediction of the theory. The electron components of the incident and reflected waves are observed to vanish within the quasineutral layer close to the grid where the plasma density rapidly drops. Furthermore it is shown that the reflected wave is a downstream wave that propagates on the ion beam that originates on the other side of the grid.

Structure of the Plasma Boundary Layer at a Conducting Sphere

The spatial distributions of the ion density and the space potential in the boundary layer at a conducting sphere of 2.5-cm radius are measured with a small movable cylindrical probe. The measured density distributions are in good agreement with the theory of Lam in the collisionless case and with the diffusion model in the collision-dominated limit. The existence of a near-Boltzmann distribution of the electrons in the collisionless quasineutral layer is demonstrated by a plot of the logarithm of the ion density versus space potential. The electron temperature obtained from this plot, from the floating potential of the sphere, and from the characteristic of the small probe differ from each other by at most 12%. A new method to detect deviations from the Boltzmann distribution in the transitional layer is tested. The ion densities measured by using the sphere as a probe agree within 13% with those obtained with the small cylindrical probe in the collisionless case.