Redistribution Of Electric Field Research Articles

Electric field redistribution and electroluminescence response time in polymeric light-emitting diodes

The electric field redistribution due to injected and trapped charge carriers in Langmuir–Blodgett (LB) films of poly(3-hexylthiophene) (P3HT) sandwiched between indium tin oxide and aluminum (Al) electrodes as function of applied voltage has been studied using charge collection measurements by the time-of-flight technique. For μτE<d (the drift distance shorter than the interelectrode distance) the amount of the collected photocharge is a function of electric field near the Al electrode and has been used to probe the time evolution of it. The response time for the field to redistribute inside the P3HT LB film was found to be of the order of 5–200 μs, in good agreement with the delay time observed in time-resolved electroluminescence measurements in light-emitting diodes (LED) of similar LB films. We suggest a model for the response times in organic LEDs based on these results.

The influence of deeply-trapped charge on the transient photocurrent response of a-Si:H solar cells

We investigated the transient photocurrent response of pin solar cells based on hydrogenated amorphous silicon to a step-wise switch-on of illumination. We consider a systematic experimental and numerical modelling study of the dependence on temperature and the length of dark time intervals before switching-on of homogeneous generation of carriers within the solar cell. The increase of experimentally achieved photocurrent transients with typical rise times in the millisecond range reflects tail thermalisation and recharging of dangling bonds. For temperatures below 175 K, the transients overshoot over the stationary values. Height and position vary with the dark time. Device modelling reproduces the experimentally observed properties. We find the recharging of defect states and hole trapping into valence band tail states resulting in a redistribution of the built-in electric field, which affects the transient behaviour. The photocurrent decrease after an overshoot is explained by a decrease of the field in part of the i layer. Consequently, less efficient carrier extraction results in a delayed onset of recombination at dangling bonds near the n layer.

Pulsed response of an MSM photodiode at high optical radiation energies

A two-dimensional model framework is used to study the effects associated with a redistribution of an internal electric field under the influence of a space charge induced by a nonuniform rate of separation of photo generated carriers at high energies of optical excitation of a metal — semiconductor — metal (MSM) photodiode. This results in a considerable distortion of the pulsed response of the photodiode, and in reduction of the efficiency and of the pass bandwidth of the photodiode. The conditions are found under which the influence of screening of the internal electric field on the response signal profile of the photodiode is unimportant.

Traps in GaAs detectors (before and after irradiation) and electric field redistribution in excited SI-GaAs

We report here on investigations of non-equilibrium conductivity and different types of defects in SI-GaAs, analyzing the effects of different growth techniques and thermal treatments. The influence of local inhomogeneities on the determination of electrical properties and parameters of local levels are discussed. The interaction of dislocation related defects and their charge have been recognized as the main factors influencing non-equilibrium carrier behaviour. The GaAs irradiation effects could be analyzed in terms of formation of microinhomogeneities, with different non-equilibrium carrier drift and capture in the inhomogeneity volume and the surrounding defect-free region. The trap spectra were studied using thermally stimulated current and polarization measurements. EL2 centre modification was used to separate electron and hole traps. Data from measurements of Hall and photo-Hall effects and light-induced non-linear optical effect measurements have also been used in the analysis.

Effect of electric field redistribution on the electronic and optical properties of nanostructures

Effect of electric field redistribution on the electronic and optical properties of nanostructures

Vliyanie pereraspredeleniya elektricheskogo polya na elektronnye i opticheskie svoistva nanostruktur

Vliyanie pereraspredeleniya elektricheskogo polya na elektronnye i opticheskie svoistva nanostruktur

Benign mechanism giving rise to kinks inGaAs MESFET and HEMT I(V)characteristics

Kinks in GaAs MESFET and HEMT I(V) characteristics may arise from a change in the depletion layer dimensions caused by redistribution of the two-dimensional electric field when the space-charge layer reaches the drain-side recess edge. The mechanism is benign in that it does not question material quality and growth.

Electric and Photoelectric Properties of High Porosity Silicon

AbstractThe basic problems of porous silicon (PS) transport, like long time constants, ageing, and the influence of contacts are discussed. The results of the steady‐state and transient photoconductivity on the self‐supporting p‐ and n‐type PS are presented and the resulting conclusions, related to the microstructure isotropy, trapping, and time‐dependent electric field redistribution are summarized. On the basis of the dark I–U characteristics and their temperature dependencies the different volume and surface transport mechanisms are discussed. The compatibility of the models of explanation of the strong PS photoluminescence with our transport results is discussed.

Photoconductivity study of self-supporting porous silicon

The study of the steady state and transient photoconductivity (PC) of p- and n-type porous silicon (PS) self-supporting layers allows us to eliminate the influence of a crystalline Si substrate on the PC. A photovoltaic effect was observed in sandwich geometry for short wavelength illumination and for long wavelengths (−580 nm) a broad photoconductive maximum was found. An explanation of both effects is proposed. Transient photoconductivity has revealed a redistribution of the inner electric field after 1–10 ms and it is proposed here as a new tool for the study of PS.

Effects of high space-charge fields on the response of microwave photodetectors

We present simulation results, based on a one-dimensional p-i-n photodetector model, to explain the reductions in photodetector response observed at high optical powers. The nonlinear effects are attributed to the redistribution of the internal electric field due to space-charge effects created by the photocarriers. The corresponding modification of the position-dependent charge velocities results in high-frequency response reduction, roll-off reduction, and pulse narrowing. Electric field redistribution leads to two dimensional effects, which must be included for accurate modeling of milliampere photocurrents. >

Theoretical investigation of transient space-charge-limited current for dispersive transport in amorphous silicon

Abstract Transient space-charge-limited current for dispersive transport in amorphous silicon has been theoretically investigated, including the multiple trapping process of carriers in a continuous distribution of trap states and the influence of injected carriers upon the electric field redistribution. The results show that for the case of electrode injecting current caused by a step voltage the current before a space-charge-limited transit time is equal to where μd(t) is the time-dependent drift mobility, qn 0, is the density of injected charge, e is the permittivity, L is the thickness of the sample, V is the applied voltage. x1 is the leading edge position of the carrier package, which can be expressed as if an exponential distribution of tail states is assumed, where μ0 is the band mobility, α is the dispersive parameter and w 0 is the thermal emission frequency. After a transit time the current decays as t −(α+1) until the final steady-state space-charge-limited current is reached. The transit time...

On the origin of the hot-electron instabilities inn-InSb at crossed electric and magnetic fields

Coherent current oscillations with frequencies of several hundreds of megahertz and microwave generation at frequencies up to 40 GHz were investigated in then-InSb samples subjected to crossed electric and magnetic fields. They are shown as being caused by electric field redistribution and negative differential mobility in high-field regions.

Self-electrophoresis of membrane molecules and chromosomes: Unifying hypothesis of cell cycle controls

A hypothesis is proposed that the decoding ability of the cell membrane to various factors promoting cell growth and division (hormones, growth factors, antigens, etc.) is based on movement and aggregation of the ligand-receptor complexes and other charged membrane subunits by self-electrophoresis in the plane of the membrane. This mechanism is proposed to be involved in two main membrane functions. It is responsible for activation and regulation of membrane-bound enzymes such as the adenylate-guanylate cyclase control system by directing the ligand-receptor complex to the distant acceptor structure (the separate cyclase molecule). Self-electrophoresis of charged subunits in the plane of the membrane causes furthermore changes in the local surface charge density of the membrane. This, through the effect on the local surface tension, which is the tractional force of the cell, causes either contraction or expansion of the cell membrane and produces the phenomena of pinocytosis and microvilli formation respectively. The self-electrophoresis hypothesis predicts that microvilli are electric entities which provide visual markers of the number and distribution of local electric fields of the cell. Elaboration of a great many randomly distributed microvilli during interphase causes depolarization of the cell which in turn has the following consequences in regard to the co-ordination of the cell cycle events. (1) The depolarized state, i.e. increased intracellular Na + content is a pre-requisite for DNA synthesis. (2) Depolarization causes unfolding of previously-accumulated microvilli. This process begins at the polar areas and is responsible for cytokinesis. (3) The unfolding of microvilli at the poles is accompanied by redistribution of the local electric fields of the cell: A great many randomly distributed fields (in interphase) are replaced by one equator-to-poles electric field (in mitosis). Since microtubules and microfilaments as well as their constituent subunits have a permanent electric dipole moment along the longitudinal axis, their reversible assembly-disassembly is controlled by these changes in distribution of local electric fields of the cell. The daughter chromosomes are separated by self-electrophoresis in the equator-to-poles electric field during anaphase.