Approximate calculation of current in a diode with an explosive emission cathode

The approximation of electron motion along electric field force lines is used to calculate current in diodes with knife-edge and point emitters. The diode current is limited by space charge, with each current tube considered as a diode element with electrodes in the form of coaxial cylinders or concentric spheres. The effect of the cathode cavity in which the emitter is installed upon current magnitude is considered by limiting beam dimensions at the anode.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 3–6, February, 1992.     

On the one-electron theory of crystalline solids in a homogeneous electric field

Assuming that the one-electron states of a perfect crystalline solid are known, an approach for the calculation of the one-electron states in the presence of external fields and/or other deviations from the periodic potential of the perfect crystal is suggested. The treatment is based on the Wannier representation and the use of a method for solving some operator non-polynomial differential equations. In the approximation of the one-band Wannier equation an exact solution of the problem for electron states of the crystals in a homogeneous external electric field is given. The results obtained in the tight binding approximation for cubic crystals show that the electron motion along the field is finite and the degree of its finiteness for a given electric field strength is greater, the smaller the width of the initial energy band considered. In the one-band approximation Considered the electron energy spectrum has the character of the Wannier-Stark ladder. It is also shown that an influence of transverse motion on the character of the finite motion along the field appears when a non-additivity in the initial energy band function with respect to the energies of motions parallel and perpendicular to the field direction is present.     

Semiconductor nanocylindrical layer in a strong electric field: Spectrum of carriers and intraband transitions

The single-electron states in a quantized cylindrical layer in the presence of a strong homogeneous electric field have been considered in the isotropic effective mass approximation. The energy spectrum and the envelope wave functions of charge carriers in the layer have been obtained in the explicit form. It has been shown that a strong external electric field leads to an additional localization of carriers in their angular motion. The corresponding selection rules have been derived, and the absorption band of intraband-intersubband optical transitions in the layer has been calculated.     

Influence of constant electric field on generation of higher harmonics in semiconductor carbon nanotubes

The generation of higher harmonics by semiconductor carbon nanotubes in the presence of constant electric field polarized along the nanotube axis is considered. The analysis is performed in the semiclassical model of electron motion without taking into account interband transitions. The electron system of carbon nanotubes is described using the kinetic Boltzmann equation in the relaxation time approximation. The dependence of higher harmonic amplitude on the field characteristics is studied.     

Dynamics of resonant and non-resonant tunneling in asymmetric coupled quantum wells

Within the framework of the effective mass approximation, coherent oscillations of a photoexcited electron wave packet in an asymmetric coupled quantum well structure have been studied using a time-dependent Schrödinger equation. In the method of calculation, the continuity of the current across a semiconductor heterojunction is considered. The amplitude and period of the electronic is obtained and in the case of high bias, it is found the existence of electric field-induced tunelling to semiconductor bulk.     

驻波加速管中的电子反轰现象

在以半腔为首腔的边耦合驻波加速管中观察到了电子反轰现象,由于电子反轰的结果,导致电于枪发射电流非正常增长。本文从纵向运动方程出发,用相轨道方法分析了驻波加速管中的电子反轰运动,并计算了不同电场分布、不同电场幅值及不同注入电压对电子反轰的影响。     

On nonlinear dynamics of a sheet electron beam

The nonstationary model is considered allowed to describe the sheet electron beam dynamics with nonuniform current density profile in collisionless approximation. The kinetic distribution function is used dependent on the particle motion integral, so the distribution function automatically satisfies to Vlasov equation. The results of numerical and analytical calculations are discussed.     

Monte Carlo simulation of in-plane spin-polarized transport in GaAs/GaAlAs quantum well in the three-subband approximation

We develop a Monte Carlo (MC) tool incorporated with the three-subband approximation model to investigate the in-plane spin-polarized transport in GaAs/GaAlAs quantum well. Using the tool, the effects of the electron occupation of higher subbands and the intersubband scattering on the spin dephasing have been studied. Compared with the corresponding results of the simple one-subband approximation model, the spin dephasing length is reduced four times under 0.125\,kV/cm of driving electric field at 300K by the MC tool incorporated with the three-subband approximation model, indicating that the three-subband approximation model predicts significantly shorter spin dephasing length with temperature increasing. Our simulation results suggest that the effects of the electron occupation of higher subbands and the intersubband scattering on the spin-dependent transport of GaAs 2-dimensional electron gas need to be considered when the driving electric field exceeds the moderate value and the lattice temperature is above 100K. The simulation by using the MC tool incorporated with the three-subband approximation model also indicates that, under a certain driving electric field and lattice temperature, larger channel widths cause spins to be depolarized faster. Ranges of the three components of the spins are different for three different injected spin polarizations due to the anisotropy of spin--orbit interaction.     

Current saturation in CdS

An iteration procedure for calculating the high electric fields found in piezoelectric semi-conductors beyond the onset of current saturation is described. The procedure uses a wave equation derived from the well known formula for electron mobility of Feynman, Hellwarth, Iddings and Platzman in which the lattice coordinates have been removed. The zero order state in the procedure is that of electrons pursuing a constant velocity path, (infinite effective mass approximation), the velocity being taken at a phase velocity of acoustic shear modes. To the next order electrons are bound by and oscillate in a quasi-potential, which itself travels at the shear wave velocity. Electrons in a single well act coherently in producing a potential strong enough to bind them despite their Coulomb repulsion. We estimate the number of electrons bunched into a single droplet, as well as the electric field to sustain this motion, i.e. the field in the high field domain.     

Thermal instability of a reconnecting current layer as a trigger for solar flares

The stability of small perturbations of a reconnecting current layer (CL) in a plasma with a strong magnetic field has been investigated in the approximation of dissipative magnetohydrodynamics. The case where the wavevector of the perturbations is parallel to the electric current in the CL has been considered. The suppression of plasma heat conduction by a magnetic field perturbation inside the CL is shown to be responsible for the instability. At the linear stage of instability development, the perturbations grow with the characteristic radiative plasma cooling time calculated in the approximation of an optically thin plasma with cosmic abundances of elements. The formation of a periodic structure of cold and hot magnetic flux tubes, viz., filaments, located across the direction of the electric current, should be expected at the nonlinear stage of the instability in the CL. The proposed mechanism of the thermal CL instability can explain the sequential brightening (ignition) in the arcades of magnetic loops in solar flares.     

Bifurcation phenomena of photodetached electron flux in parallel external fields

A semiclassical method based on the closed-orbit theory is applied to analysing the dynamics of photodetached electron of H$^- $ in the parallel electric and magnetic fields. By simply varying the magnetic field we reveal spatial bifurcations of electron orbits at a fixed emission energy, which is referred to as the fold caustic in classical motion. The quantum manifestations of these singularities display a series of intermittent divergences in electronic flux distributions. We introduce semiclassical uniform approximation to repair the electron wavefunctions locally in a mixed phase space and obtain reasonable results. The approximation provides a better treatment of the problem.     

Dynamics of electronic and nuclear motion in a molecular hydrogen ion in a strong laser field

The dynamics of the electron and ion subsystems of a molecular hydrogen ion in the field of femtosecond titanium-sapphire laser radiation is investigated by using numerical simulation. The dependence of the probability of ionization and excitation of various electron states of H ₂ ⁺ on the radiation intensity and on the orientation of the molecule axis relative to the direction of polarization of the electric field of the wave is investigated. It is shown that the population of all electronic states of the molecule (except the ground state and the first excited state) is negligibly low in a wide range of radiation intensity. In such a situation, if the probability of system ionization is also low, the dynamics of vibration-rotation motion of nuclei in the molecule can be considered in the approximation of two potential surfaces (energy levels). The possibility of the effective orientation of the molecular axis along the direction of the electric field of the wave in the absence of dissociation of the system is considered.     

Photocurrent in a two-dimensional ribbon with the conic electron spectrum

The strips of graphene or 2D HgTe with the conic electron spectrum illuminated by interband radiation are studied under the assumption of motion of classical carriers. Linearly polarized radiation produces optical orientation of electron momenta. The asymmetry of edges together with the radiation polarization leads to electric current along the strip. The cases of narrow and wide strip with respect to the mean free path are considered. Besides, the edge photocurrent is investigated in a wide strip, one of edge of which is illuminated. We show that electron–electron collisions play an important role by violating e–h symmetry that provides the overall current.     

A physics-based potential and electric field model of a nanoscale rectangular high-K gate dielectric HEMT

In this paper, we have developed a physics-based model for surface potential, channel potential, electric field and drain current for AlGaN/GaN high electron mobility transistor with high-K gate dielectric using two-dimensional Poisson equation under full depletion approximation with the inclusion of effect of polarization charges. The accuracy of the model has been verified and is found to be in good agreement with the simulated results.     

Theoretical Analysis of the Resonance Cone in an Inhomogeneous Magnetoplasma Column

The three-dimensional behavior of the high-frequency resonance cone is investigated using an inhomogeneous slab magnetoplasma model under the quasi-static approximation and neglecting ion motion. The effects of finite ky and electron thermal motion are considered numerically, revealing that the cone angle is shifted to a slightly smaller angle and the reflection point is also shifted toward the high density region compared with results under the cold plasma approximation.     

Controllable electron dynamics in a finite-size quantum well lattice

The nonstationary electron dynamics in a quantum well lattice is considered. We investigate the influence of quasi-constant electric field applied to the system in addition to variable electric field periodic in time. It is shown that various types of controllable motion of an electron density in the lattice can be realized.     

Use of the BFCPIC and BFCRAY codes to describe space charge limited emission in electron guns for gyrotrons

Numerical modelling of an electron gun in the space charge limited regime requires determining the current density distribution as well as the electric fields and electron trajectories. This is a rather complicated self-consistent problem, since the space charge influences the electric field, which in turn influences the electron trajectories. Previous simulations of magnetron electron guns using the BFCPIC and BFCRAY codes used a simple emission model (constant current density) that is approximately valid for thermionic emission. The code has been modified to include space charge limited emission. Several different ways of doing this are considered. One of the models considered uses Gauss’s law to force the electric field on the emitter to vanish; it was used in the original version of BFCPIC for the simulation of ion diodes. A second is based on the use of Child’s law (locally), which may be more appropriate for extension to fully electromagnetic particle-in-cell (PIC) codes. Calculations were performed with both models, and the results compared with each other and with experiments performed at FZK.     

On The Motion of Ions in The Self-sustaining Magnetically Confined Electron Cloud

The motion of ions generated from the electron-atom ionization collisions in the self-sustaining magnetically confined electron cloud is studied.It is shown that the motion is chaotic.The method to determine the electric potential idstribution in the electron cloud by measurements of the ion current is discussed.     

Semiconductor electrons in electric and magnetic fields

Optical properties of semiconductors in the simultaneous presence of electric and magnetic fields are reviewed, with particular emphasis on the possibilities of modulation techniques. First, the problem of an electron in crossed and parallel fields is solved in the one-level effective mass approximation (EMA), and the results are used to interpret the experimental interband transitions in Ge, with due account of the degenerate character of the valence band in this material. The limitations of the one-level EMA are discussed, and the two-level model is introduced, which correctly describes the experimentally observed transition from a magnetic type to an electric type of motion in increasing transverse electric field. Possibilities to observe electric field effects in cyclotron resonance transitions are discussed in this approximation. Finally, the three-level model is used to describe properly both orbital and spin properties of conduction electrons. It is demonstrated that in a small-gap semiconductor with large spin-orbit interaction a sufficiently strong transverse electric field destroys the Landau orbital quantization but not the Pauli spin quantization. Possible experimental consequences of this situation are discussed. Influence of finite dimensions of the sample on the character of the electron motion in crossed and parallel fields is examined. A possibility to achieve the semiconductor-semimetal transition in a symmetryinduced zero-gap semiconductor in crossed field configuration is predicted and described, taking into account the Luttinger effects in the magnetic level structure.     

Coefficients of diffusion and conductivity of semiconductor carbon nanotubes in an external electric field

The coefficients of electron diffusion and conductivity have been calculated for single-layer semiconducting carbon nanotubes in an external electric field with the strength vector directed along the nanotube axis. The evolution of the electronic system of the nanotubes has been described using the Boltzmann kinetic equation in terms of the quasi-classical approximation of relaxation time. An analytical expression of the electron diffusion coefficient has been obtained, and its nonlinear field dependence has been revealed.