Current filamentation

Richard Williams, Injection by Internal Photoemission Allen M. Barnett, Current Filament Formation R. Baron and J.W. Mayer, Double Injection in Semiconductors W. Ruppel, The Photoconductor-Metal Contact... 

R Williams, Injection by Internal Photoemission A. M. Barnett, Current Filament Formation... 

Figure 75. Current filaments in p-Ge at various voltages, made visible by the EBIC technique (electron beam induced currents). 274 (Reprinted from K. M. Mayer, R. Gross, J. Parisi, J. Peinke, R. P. Huebener, Spatially Resolved Observation of Current Filament Dynamics in Semiconductors. , Solid State Commun., 63, 55-59. Copyright 1987 with permission from Elsevier.)...

This lamp produced the best replication of sunlight, to date, had the greatest amount of light output (foot-candles) per watt, produced the least amount of heat and was more efficient than the current filament lamps. A blower was incorporated in the cabinet design to remove the heat generated by the lamps and their ballasts, which was still substantial. 

When the simulation runs and the plasma populations stream through each other, we observe how the Weibel instability collects particles into current filaments (Medvedev and Loeb, 1999). First the electrons go through the instability and then further downstream the electrons thermalize to one single population and the heavier ions goes through the instability. 

The ion filaments are more robust than the preceding electron filaments since the thermalized electron will Debye shield the ion filaments. Even further downstream the current filaments acts as 2D macro particles in the transverse plane and are themselves collected into larger filaments as explained by Frederiksen et al., 2004 and Medvedev et al., 2004. This behavior can be seen in fig. 1. 

Figure 1. This figure shows the generation of ion current filaments. Here we see the jet head on. The four slices show the ion current density at different depths of the shock at a fixed time. The different depths are z= 60, 100, 120, 160 electron skin depths.

We have performed numerical experiments of relativistic collisionless plasma shocks using a self-consistent three dimensional particle-in-cell code. We find that the Weibel instability is capable of generating turbulent magnetic fields with a strength up to percents of equipartition. The magnetic field is induced around ion current filaments. These filaments also accelerates electrons to power law distributions. The suggested acceleration scenario does not rule out ion Fermi acceleration but might overcome some of the problems pointed... 

A. Alekseev, S. Bose, P. Rodin, and E. Scholl Stability of current filaments in a bistable semiconductor system with global coupling, Phys. Rev. E 57, 2640 (1998). 

Inasmuch as electric charges are absent, the induced currents as well as the primary vortex electric field Eq, have only an azimuthal component in the cylindrical system of coordinates r, 0, (Fig. 3.4). It is obvious that interaction between current filaments does not change the direction of current flow in this case. Thus the total electric field is ... 

As was shown in Chapter 1 a circular current filament passing an elementary current tube at the point q creates the vortex electric field at point p (Fig. 3.4c) equal to ... 

The function G k2, p, q) describes with accuracy of a constant the electric field in a uniform medium with conductivity current filament. As will be shown in the next chapter it can be expressed through the proper integral from the elementary function. 

High-current filamentous channel bridges the electrode gap. 

In all real systems, some deviation from ideal behavior can he observed. If a potential is applied to a macroscopic system, the total current is the sum of a large number of microscopic current filaments, which originate and end at the electrodes. If the electrode surfaces are rough or one or more of the dielectric materials in the system are inhomogeneous, then all these microscopic current filaments would be different. In a response to a small-amplitude excitation signal, this would lead to frequency-dependent effects that can often be modeled with simple distributed circuit elements. One of these elements, which have found widespread use in the modeling of impedance spectra, is the so-called constant phase element (CPE). A CPE is defined as... 

As shown in Figure 6.1(c) the conducting branch of the threshold switch is nearly vertical. The precise I—V relationship of the ON-state is obtained by subtracting the spreading resistance in the electrodes adjacent to the current filament and, in thin film devices, by subtracting the additional strip resistance of the thin metal films. Lee (1972) reports that he obtained 1 OL for the ON-state characteristic. 

The memory action in the chalcogenide glass memory devices is based on the reversible crystallization and revitrification of the material in the current filament of the switched-on state. The size and duration of the SET pulse governs the diameter of the SET filament and thus the impedance of the ON state. In the example of Figure 6.13 the OFF and ON impedance states were 10 ohms and 20 ohms, respectively. 

More device characteristics will be presented in the following section which summarizes the present device development. A later section describes details of the physical changes in the current filament which are responsible for the memory action. 

Barnett, A. M., Chapter 3 current filament formation, in Semiconductors and Semimetals, Vol. 

Fig. 6.79 Current filaments in p-Ge at various voltages, made visible by the EBIC technique (electron beam-induced currents). Rom Ref. [520].

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