Trapped Distribution Function Research Articles

Particle Trapping in Axisymmetric Electron Holes

AbstractElectron orbits are calculated in solitary two‐dimensional axisymmetric electrostatic potential structures, typical of plasma electron holes, in order to establish the conditions for the particles to remain trapped. Analytic calculations of the evolution of the parallel energy caused by the perturbing radial electric field (breaking magnetic moment invariance) are shown to agree well with full numerical orbit integration Poincaré plots. The predominant mechanism of detrapping is resonance between the gyrofrequency in the parallel magnetic field and harmonics of the parallel bounce frequency. A region of phase space adjacent to the trapped‐passing boundary in parallel energy is generally stochastic because of island overlap of different harmonics, but except for very strong radial electric field perturbation, more deeply trapped orbits have well‐defined islands and are permanently confined. A simple universal quantitative algorithm is given, and its results plotted as a function of magnetic field strength and hole radial scale length, determining the phase space volume available to sustain the electron hole by depression of the permanently trapped distribution function.

Investigating the energy spectrum of silicon nanoclusters in a silicon dioxide matrix

This paper presents the results of an investigation of the energy spectrum of traps that occur in a silicon nanocomposite created using the new “elion” technology—low-temperature laser modification of the surface of a layer of nanoporous silicon in the medium of a strong gaseous oxidant. Combined analysis of the transmission spectra of laser-oxidized nanoporous silicon and the trap-distribution function over the activation energy made it possible to explain the presence of selective absorption in the IR region.

Trap spectroscopy by the glow rate technique using bleaching of colour centres.

An application of the glow rate technique (GRT) for analysis of the parameters of thermostimulated decay of colour centres is presented using the data on the decay of radiation defects in LiBaF3:Fe crystals created by X rays at 300 K. The GRT offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by the trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated decay kinetics at different heating rates. It is shown that the decay of the F type centres is governed by interaction of mobile anion vacancies with F(A) and F centres, leading to both the hopping migration and recombination of F centres and the thermoactivated dissociation of the F(A) centres.

Advanced trap spectroscopy using the glow rate technique based on bleaching of color centers

The glow rate technique (GRT) is the extension of the known heating rate method to the full glow curve. The GRT like the fractional glow technique (FGT) offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated recombination kinetics at different heating rates. The extension of the GRT to the direct measurements of thermostimulated bleaching of the radiation-induced color centers is presented. The experimental procedure involves measurements of the decay of radiation-induced absorption spectra of color centers in preliminary irradiated materials during linear heating. Procedure for evaluation of the trap energy and frequency factor spectrum is considered in the paper. Results of the application of GRT for analysis of the parameters of thermostimulated decay of color centers are presented in the case of decay of the radiation-induced defects in LiBaF 3 crystals irradiated by X-rays. It is shown that decay of F-type centers occurs in two steps, the activation energy slightly decreasing from 0.660±0.003 eV in the first step (300– 370 K ) to 0.615±0.003 eV (400– 480 K ) in the second step.

A new charge pumping model considering bulk trap states in polysilicon thin film transistor

This paper proposes a new charge pumping model (bulk state model) in a polysilicon thin film transistor. The charge pumping current is calculated both from the bulk state model and the conventional model (interface state model) and each of them is compared with the measured data. In the bulk state model, the threshold voltage is defined as the gate voltage when the trapping time constant, which is a function of free electron concentration, is equal to the applied gate-pulse width. By applying this definition to each depth, the threshold voltage can be calculated as a function of depth. The threshold voltage shift is also taken into account to calculate the threshold voltage. From the threshold voltage, two associated emission energy levels are calculated. On the basis of the data from the field-effect conductance method, we assume that the trap distribution function is composed of two tails and two Gaussian functions. For each depth, the charge pumping current density is calculated by integrating the trap distribution function between two emission energy levels in silicon band gap. The charge pumping current is calculated by integrating the charge pumping current density with respect to depth. It shows that the calculated current of the bulk state model is more consistent with that of the measured rather than that of the interface state model.

Time-dependent charge trap distribution function in polyaniline films

Relaxation processes of photoconductivity in emeraldine base (non-conductive form of polyaniline) are investigated under nanosecond laser excitation. Photocurrent relaxation data are approximated well by the stretched exponential function F1(t) = A1 exp[−(t/τstr)β] in the time interval from 0.45 to 40 ms. It was found that the parameters τstr and β of the function F1(t), which also characterize the energy distribution function of the electron traps, increased with time and allow an estimation of the decrease of the averaged trap depth dispersion in time. These parameters also demonstrated irregular behavior in the temperature range 180–300 K, forming a broad maximum at the temperatures of β-transition to the torsional motion of the rings along the polymer backbone in polyaniline from 180 to 260 K. © 1998 John Wiley & Sons, Ltd.

Time‐dependent charge trap distribution function in polyaniline films

Time‐dependent charge trap distribution function in polyaniline films

Perpendicular heating of electrons by upper hybrid waves generated by a ring distribution

Satellite observations of electron conical distributions with enhanced fluxes just outside the loss cone suggest that electrons have been heated perpendicularly to the magnetic field in the mid‐altitude polar magnetosphere. To understand electron conical distributions, plasma simulations are conducted to examine an upper hybrid wave instability of a ring electron distribution perpendicular to the magnetic field in a cold electron background. The simulations indicate that both the cold and ring distributions are heated perpendicularly during the saturation stage. From the plasma data, a ring distribution can be identified as a trapped distribution function with an enhancement near 90° pitch angle in the phase space density plot. It is suggested that the ring distribution might provide an additional free energy source for generating upper hybrid waves associated with electron conical events.

Trap spectroscopy by the fractional glow technique

A theory of the fractional glow technique (FGT) for an arbitrary heating regime and first-order recombination kinetics is developed. In order to describe a trap distribution function (TDF) its characteristics: (i) the mean activation energy, (ii) the mean frequency factor, (iii) the recombination intensity, (iv) the FGT energy spectrum as the TDF image in activation energy scale, and (v) the FGT frequency factor spectrum as the TDF image in frequency factor scale are presented. Relations are obtained which permit direct calculation of these characteristics without a computer simulation of the fractional heating regime. Regularities of the FGT energy spectrum formation as well as the errors of the mean frequency factor estimate for various TDF's are discussed.

Characterization of low 1/f noise in MOS transistors

By careful processing MOS transistors have been fabricated with a low value of the interface states density (2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> eV). Consequently the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/f</tex> noise in these devices is low and in the same order of magnitude as for junction FETs. The experimental values of the equivalent noise voltage and the equivalent noise current are compared to an expression derived from straight physical arguments. From the comparison it is concluded that the noise equivalent voltage in saturated operation is proportional to the effective gate voltage, the interface state density, and inversely proportional to the gate input capacitance. Moreover, it is concluded that a proper heat treatment not only reduces the number of states but also removes the near bandedge peaks, which usually appear in the trap distribution function.