Drift Electric Field Research Articles

Validation of the stream function method used for reconstruction of experimental ionospheric convection patterns

In this study we test a stream function method suggested by Israelevich and Ershkovich for instantaneous reconstruction of global, high-latitude ionospheric convection patterns from a limited set of experimental observations, namely, from the electric field or ion drift velocity vector measurements taken along two polar satellite orbits only. These two satellite passes subdivide the polar cap into several adjacent areas. Measured electric fields or ion drifts can be considered as boundary conditions (together with the zero electric potential condition at the low-latitude boundary) for those areas, and the entire ionospheric convection pattern can be reconstructed as a solution of the boundary value problem for the stream function without any preliminary information on ionospheric conductivities. In order to validate the stream function method, we utilized the IZMIRAN electrodynamic model (IZMEM) recently calibrated by the DMSP ionospheric electrostatic potential observations. For the sake of simplicity, we took the modeled electric fields along the noon-midnight and dawn-dusk meridians as the boundary conditions. Then, the solution(s) of the boundary value problem (i.e., a reconstructed potential distribution over the entire polar region) is compared with the original IZMEM/DMSP electric potential distribution(s), as well as with the various cross cuts of the polar cap. It is found that reconstructed convection patterns are in good agreement with the original modelled patterns in both the northern and southern polar caps. The analysis is carried out for the winter and summer conditions, as well as for a number of configurations of the interplanetary magnetic field.Key words: Ionosphere (electric fields and currents; plasma convection; modelling and forecasting)

Cathodoluminescence analysis of cleaved facets of a ZnSe p–n junction

ZnSe diodes grown on (100) GaAs substrates by molecular beam epitaxy were investigated using cathodoluminesence (CL) measurements at sample temperatures between 50 and 300 K. The CL line scans at different photon energies were performed on cleaved p–n junctions at 50 and 300 K, respectively. Taking into account surface recombination, carrier generation volume, carrier diffusion and internal built-in electric field and related carrier drift, the CL measurements from cleaved p–n junctions could be qualitatively explained. The charge depletion layer has a strong influence on the CL measurements. The calculated charge depletion width is in good agreement with CL measurements. The experimental data from the spatially resolved CL on the cleaved ZnSe diodes revealed important information of the carrier dynamics and recombination processes in these devices.

Fast silicon drift photodiodes free from bias connections on the light entering side

A new type of silicon drift photodiode intended to be coupled to large area scintillators is described. The diodes have a relatively large area (1 cm 2) and a short maximal drift time (300 ns). They operate without requiring any external electrical connection at the side of the photodiode coupled to the scintillating crystal. These new photodiodes have almost identical ring structures on both sides with individual rings being at linearly increasing potentials providing the required high electric drift field. A new feature of the presented photodiodes is a small modification of the electrode structure near the signal collecting anode. It allows a full depletion of the photodiode and the highest drift field. Advantages and drawbacks of this kind of photodiodes are described.

High field electron transport properties of bulk ZnO

The Monte Carlo method is used to simulate electron transport for electric field strengths up to 350 kV/cm in bulk, wurtzite structure ZnO. The relevant parts of the conduction bands of a first-principles band structure are approximated by spherically symmetric, nonparabolic valleys located at the Γ and Umin symmetry points of the Brillouin zone. It is shown that the analytic expressions represent the band structure and the density of states well over a range of nearly 5 eV from the bottom of the conduction band. The simulated electron steady-state drift velocity versus electric field characteristics are calculated for lattice temperatures of 300, 450, and 600 K. For room temperature, drift velocities higher than 3×107 cm/s are reached at fields near 250 kV/cm. Examination of the electron energy distributions shows that the strong decrease of the differential mobility with increasing electric field in the field range studied is to be associated with the pronounced nonparabolicity of the central valley and not with transfer of electrons to satellite valleys.

Cross Section Potentiometry of Doped Silicon Structures Using SFM

The surface work function measurement of doped silicon structures by using an adapted commercially available SFM (scanning force microscope) is presented. The investigation of a well defined ion-implanted sample for testing the measurement method is described. Deviations of the measured work function values from the theoretical expectations are discussed and interpreted. Furthermore the cross-sectional measurement of a microcrystalline silicon p–i–n diode structure for photovoltaic applications is presented. Contrast can be achieved due to different dopants and the built-in electric drift field between p- and n-doped regions. The potential to judge the quality of diode structures and to suggest improvements for the deposition process is stated.

Cross Section Potentiometry of Doped Silicon Structures Using SFM

The surface work function measurement of doped silicon structures by using an adapted commercially available SFM (scanning force microscope) is presented. The investigation of a well defined ion-implanted sample for testing the measurement method is described. Deviations of the measured work function values from the theoretical expectations are discussed and interpreted. Furthermore the cross-sectional measurement of a microcrystalline silicon p–i–n diode structure for photovoltaic applications is presented. Contrast can be achieved due to different dopants and the built-in electric drift field between p- and n-doped regions. The potential to judge the quality of diode structures and to suggest improvements for the deposition process is stated.

Full-band Monte Carlo model of electron and hole transport in strained Si including inelastic acoustic phonon scattering

Full-band Monte Carlo simulations of electron and hole transport in strained Si on Si0.7Ge0.3 have been performed with a transport model which includes a wave-vector-dependent inelastic acoustic phonon scattering rate. Only two unambiguously determined deformation potentials are needed to achieve excellent agreement with experimental drift velocity versus electric field data for unstrained Si over the very wide temperature range from 20 to 430 K. For strained Si, this model yields in-plane lattice mobilities of 3490 cm2/(V s) for electrons and 1760 cm2/(V s) for holes at 300 K. Drift velocity and energy versus electric field characteristics are given as reference for conventional device simulations. In contrast to simpler transport models, we do not find a pronounced Gunn effect at 77 K.

Mobility Degradation Models for Electrons in Inversion Layers of Silicon

Carrier mobility in silicon inversion layers is an important parameter that reflects carrier transport mechanisms. It is very important to accurately model the effective mobility of carriers for the accurate calculation of the drain current using device simulation programs. This becomes more important in submicron devices using higher substrate doping, thinner gate dielectrics, and much higher electric fields. Several models for the effective mobility of carriers, as a function of the effective transverse electric field in MOS inversion layers have been reported. Extraction from experimental data of parameters best fitting to an empirical formula has been used. To find out the physically appropriate model for mobility of inversion layer electrons at room temperature, we compare calculated effective mobility versus transverse electric field using recently reported empirical model for mobility degradation. The drift velocity versus electric field characteristics were calculated, using different models for mobility degradation, and compared to previously reported experimental results. The MOSFET saturation drain current, which is of most importance because of its effect on circuit speed, was calculated using these models and compared to recent theoretical and experimental results that take the effects of mobility degradation, velocity saturation and series resistance into consideration.

Electron drift and diffusion in a high electric field

Electron drift and diffusion in a high electric field

Monte Carlo simulation of electron transport properties in extremely thin SOI MOSFET's

Electron mobility in extremely thin-film silicon-on-insulator (SOI) MOSFET's has been simulated. A quantum mechanical calculation is implemented to evaluate the spatial and energy distribution of the electrons. Once the electron distribution is known, the effect of a drift electric field parallel to the Si-SiO/sub 2/ interfaces is considered. The Boltzmann transport equation is solved by the Monte Carlo method. The contribution of phonon, surface-roughness at both interfaces, and Coulomb scattering has been considered. The mobility decrease that appears experimentally in devices with a silicon film thickness under 20 nm is satisfactorily explained by an increase in phonon scattering as a consequence of the greater confinement of the electrons in the silicon film.

Three-dimensional nonlinear analysis of an E× B drifting electron laser

In this paper we numerically investigate the nonlinear evolution of the E × B drifting electron laser (DEL) [1, 2] for an amplifier configuration in which an electron beam propagates through a periodic magnetic field (wiggler) and undergoes a relativistic E × B drift in orthogonal static electric and magnetic fields. A set of coupled nonlinear differential equations is given in three dimensions which controls the self-consistent evolution of TE modes in a rectangular waveguide as well as the trajectories of an ensemble of electrons. Our numerical simulations are conducted to model a 35 GHz amplifier with an electron beam energy of 3.5 MeV. The results show that the radiation energy in the DEL mainly comes from the change in the kinetic energy of the electron beam, and the DEL, compared with the free-electron laser (FEL) with similar operating parameters, has higher interaction efficiency and peak power.

Monte Carlo calculation of electron transport properties of bulk AlN

The Monte Carlo method is used to simulate electron transport in bulk, wurtzite phase AlN using a three valley analytical band structure. Spherical, nonparabolic conduction band valleys at the Γ, K, and U symmetry points of the Brillouin zone are fitted to a first-principles band structure. The electron drift mobility is calculated as a function of temperature and ionized donor concentration in the ranges of 300–600 K and 1016–1018 cm−3, respectively. The effect of compensation on ionized impurity scattering and the associated change in the mobility are considered. The simulated electron steady-state drift velocity and valley occupancy for electric fields up to 600 kV/cm are presented for 300, 450, and 600 K. Our calculations predict that AlN will exhibit a much smaller negative differential mobility effect than GaN, and that the drift velocity versus electric field curve will show a very broad peak.

Coronal Transients Caused by the Drift Electric Field

When ion-acoustic turbulence is fully developed, Coulomb collision damping and Landau collisionless damping can all be neglected. Since the electric field force is greater than the damping force, a coronal transient can be created by the acceleration caused by the electric field. Eruptive prominence and coronal mass ejection (CME) events can occur as a consequence of this mechanism.

On the ion-scale structure of thin current sheets in the magnetotail

A numerical and analytical investigation of the formation and structure of thin current sheets which form in a magnetotail-like plasma model is presented. Current sheet formation is driven by the application of a boundary electric field similar to what would be expected from solar wind driving. As a result, a thin current sheet forms which involves strong Hall-type electric fields, which, by means of electric field drifts, strongly increase the electron contribution, and reduce the ion contribution to the cross-tail current density. This result is also supported by analytical investigations of the total plasma momentum. The thin current sheet forms on strong gradients in the ion density and the magnetic field. The simulation leads to a well defined equilibrium state.

Saturated electric field effect at semi-insulating GaAs-metal junctions studied with a low energy positron beam

The interfacial electric field established under different reverse bias conditions in Au and Ni on semi-insulating GaAs junctions has been studied by means of a low energy positron beam. The technique used is that of monitoring the positron drift to the interface through changes in the annihilation radiation lineshape as a function of incident positron beam energy at different reverse biases. The data show a small but clear electric field drift of positrons towards the interface that increases more rapidly at low voltages (less than 50 V) which at higher biases tends towards saturation. This confirmation of electric field saturation adds further weight to the picture of an electric field enhanced electron capture cross section for the ionized EL2 defect. Electric field values extracted from the data are compared with results from other techniques and suggest that enhanced electron capture is already occurring at the relatively low built-in fields (∼1 kV cm−1) found at the unbiased junction, with a rapid increase of EL2+ neutralization occurring for biases above 10 V. At still higher fields ∼10 kV cm−1 (biases>50 V), there appears to be an additional threshold for more complete EL2+ neutralization adjacent to the contact. The present study clearly demonstrates the often overlooked necessity of catering for built-in electric fields in positron diffusivity studies of III–V semiconductors where surface midgap Fermi-level pinning is common.

Dynamics of electron-hole plasma in semiconductor opening switches for ultradense currents

A physicomathematical model for calculating the dynamics of the electron-hole plasma in semiconductor opening switches for ultradense currents is developed. The model takes account of the real doping profile of a semiconductor p +-p-n-n + structure and the following elementary processes in the electron-hole plasma: current-carrier diffusion and drift in high electric fields, recombination on deep impurities and Auger recombination, and collisional ionization in a dense plasma. The electrical pumping circuit of the opening switch is calculated by solving the Kirchhoff equations. The motion of the plasma in the semiconductor structure is analyzed on the basis of the model. It is shown that for ultrahigh pumping levels the interruption of the current in the opening switch occurs in the heavily doped regions of the p +-p-n-n + structure and is due to saturation of the particle drift velocity in high electric fields.

Calibration of a liquid xenon gamma ray detector for the study of radiative pion decay

The performance of a liquid xenon time projection chamber as a detector for gamma rays between 0 and 30 MeV has been studied by comparing data collected with radioactive sources to a Monte Carlo simulation. The detector was designed for the study of the pion radiative decay. Both the scintillation light and the ionization charge signals were exploited. The light signals were used in the trigger logic and for the measurement of the chamber trigger acceptance. The minimum triggerable energy turned out to be 170 keV. The charge signals were used to measure the gamma ray energy. The noise introduced by the electronics was about 140 keV and the minimum measurable energy 230 keV with an electric drift field of 0.5 kV/cm. All the charge and light spectra were in good agreement with the simulation. The overall apparatus acceptance, taking into account geometry, trigger efficiency and offline reconstruction losses, was independent of the gamma ray energy above 2 MeV and equal to 10%.

Schottky barrier breakdown in Si stimulated by exciton drift in a nonuniform electric field at 4.2 K

Schottky barrier breakdown in Si stimulated by exciton drift in a nonuniform electric field at 4.2 K

Energy transport drift-diffusion model for submicrometer GaAs MESFETs

An energy transport drift-diffusion model is presented for submicron GaAs MESFETs, which accepts the physically-meaningful effective V-F characteristics depending on the distribution of the drift electric field or the drain voltage. A method expressing the relaxation time of momentum with the bulk low-field mobility is presented, which is effective for comparison between the simulations and the experiments. The characteristics are evaluated using the 1D balance equations of momentum and energy. The drift velocity is described by a double-valued function of the drift electric field. This property is caused by the inertia motion of the Γ-valley electrons for the small drain voltage and by the hot electron effect for the large drain voltage. The present results agree well with the experimental and ensemble Monte Carlo simulation ones.

High Temperature Hot Electron Transport in 6H- and 3C-SiC

The electron drift velocity and electron temperature in 6H- and 3C-SiC at 300, 673 and 1073 K ambient temperature have been calculated by using a hydrodynamic balance equation method. Our results show that the drift velocity versus electric field relation in 3C-SiC at 300 K is in good agreement with a previous Monte Carlo simulation. A gentle peak of drift velocity appears at high electric field. The velocity–field relation in 6H-SiC at 300 K agrees with the experimental data up to 500 kV/cm. At higher electric field, however, the drift velocity decreases.