Numerical investigations on the current conduction in bilayer organic light—emitting devices with ohmic injection of charge carriers

A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trappedcharge limited conduction. The dependences of the current density on the operation voltage, the thickness andtrap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure an-ode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trapdepth, total trap density, and carrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL tothe sum of HTL and EML, by which a maximal current density, and hence maximal quantum efficiency and luminance,can be achieved. The current density decreases quickly with the mean trap density, and decreases nearly exponentiallywith the mean reduced trap depth.     

Ar ion milling of InSb for manufacturing single electron devices

Ar⁺ ion milling of InSb for manufacturing single electron devices was studied. It is shown that pyramidal structures (porous) are created on the (1 1 1) surface of InSb wafers by anisotropic etching. Also it was shown the axis of the pyramidal structure is a function of the angle of the Ar⁺ incident beam and does not depend on the energy of the beam. EDX measurement results show In_xO_y and Sb_xO_y were not created on the surface after milling process. FTIR measurement results show that the surface reflection was decreased and less than 0.3 V flat band voltage was seen in capacitance voltage measurement results. SEM images show that the etching has approximately vertical profile. Therefore the Ar⁺ milling technique can be used as a dry etching technique for manufacturing mesa and/or porous structures of InSb. Since the surface is porous and of near-pyramidal morphology, one can simulate the surface by a set of needles each of which is a nanometer-size capacitance (i.e. single electron device). We showed, the threshold voltage of this single electron device is 0.3 V approximately, and therefore it can be used for studying single-electron or Coulomb blockade effects.     

A model of charge injection at metal-insulator contacts

A phenomenological model of charge carrier injection at metal-insulator contacts is proposed to quantify the injection property of such contacts, especially of non-Ohmic ones. The model contains two parameters: one is the injection current G at a given field, and the other is the field-dependence power p of the injection. It is shown that the values of G and p for a given contact can be determined from the results of step-voltage experiments. When applied to the data on Au-As₂Se₃ contact, it is found that the injection current is G≈10^?6 A cm^?2 at a field of 10⁵ V cm^?1, and the field dependence is approximately quadratic, p≈2. In addition, the field-dependence and the thickness-independence of the peak current can be explained.     

Theoretical study on spin-polarized injection of electrical currents into polymer semiconductors

Different from electrons and holes in traditional inorganic semiconductors, the charge carriers in polymer semiconductors are spin polarons and spinless bipolarons. In this paper, a theoretical model is presented to describe the spin-polarized injection of electrical currents from a ferromagnetic contact into a nonmagnetic polymer semiconductor. In this model, a new relation of conductivity to concentration polarization for polymer semiconductors is introduced based on a three-channel model to describe the spin-polarized injection of electrical currents under large electrical current densities. The calculated results of the model reveal the effects of the polaron ratio, the carrier concentration polarization, the interfacial conductance, the bulk conductivity of materials, and the electrical current density, etc. on the spin polarization of electrical currents. As conclusions, the large and matched bulk conductivity of materials, the small spin-dependent interfacial conductance, the thin polymer thickness and the large enough electrical current are critical factors for upgrading the spin polarization of electrical currents in polymer semiconductors. Particularly, when the polaron ratio in polymer semiconductors approaches the concentration polarization of the ferromagnetic contact, a modest concentration polarization is sufficient for achieving a nearly complete spin-polarized injection of electrical currents.     

一种用于堆叠结构有机发光二极管的新的电荷生成层

本文报道了一种用于堆叠结构有机电致发光器件的新的电荷生成层: LiF/Al/V₂O₅,采用这种电荷生成层的堆叠器件的两个发光单元互相独立,不受影响.说明在外加电场下,这种电荷生成层具有向邻近的发光单元注入电子空穴的能力.而堆叠了两个相同发光单元的器件的电流效率在相同的电流密度下约为普通单层结构的1.7倍.同时这种电荷生成层避免了溅射indium tin oxide(ITO)和金属、有机物共掺,只需要热蒸发,生长工艺简单. 关键词： 堆叠结构 有机电致发光器件 电荷生成层     

Coherence control of Hall charge and spin currents

Using two-color optical coherence control techniques in intrinsic GaAs at 80 K with orthogonally polarized 70 fs, 1430 and 715 nm pulses, we generate a pure spin source current that yields a transverse Hall pure charge current; or alternatively, with parallel polarized pulses, we generate a pure charge source current that yields a pure spin current. By varying the relative phase or polarization of the incident pulses, one can effectively tune the type, magnitude and direction of both the source and transverse currents without application of electric or magnetic fields.     

Particle detection properties of charge coupled devices

A detailed quantitative analysis of particle events observed in Charge Coupled Devices (CCDs) requires the knowledge of particle detection properties of the employed CCDs such as the detection threshold for energy deposition, efficiency for different kinds of radiation and the relation between the signal and the deposited energy inside the sensitive volume. For this purpose the CCD-chip was described by a simple geometrical model containing the effective thicknesses of the p-n semiconductor junctions dj and a covering dead layer d_T above them as parameters. The corresponding geometrical quantities were experimentally estimated to be 1.3 μm and 0.9 μm respectively by using different kinds of radiation.     

Study of the local repolarization currents and charge carrier injection on an LiNbO3 surface scanned with a mobile point electrode

A method of the potential relief recording and reading in a subsurface region of Z-cut monodomain lithium niobate crystals of congruent composition was developed. The method is based on scanning the crystal surface with a point (needle-like) electrode. The injection and polarization switching currents were measured in the course of scanning. It was found that the characteristic time of the potential relief formation during the injection of carriers into the subsurface crystal region is on the order of 10⁻¹ s. The process of polarization switching and the related potential relief formation is about ten times faster. For a dot recording, a characteristic distance on which a significant change in the recorded potential relief takes place is on the order of 10² μm. The carrier injection current in the +Z direction is smaller than that in the opposite direction. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 9, 2001, pp. 1669–1673. Original Russian Text Copyright ? 2001 by Zalesskii, Sherman, Fregatov.     

A study of space charge measurement

At present, there is no appropriate measurement techniques for space charge. In this paper, a U-shaped cavity device is developed as the space charge measurement device, which can be applied to transmission lines. Its design principle and calculation techniques of design parameter are also introduced. To test the space charge measurement accuracy of the U-shaped cavity device, a space charge generator is developed specifically for this experiment. The test results are excellent and show that the U-shaped cavity device can meet the design requirements. This technique is suitable for space charge measurement under transmission line normally charged work condition.     

Fabrication of ZnO and its enhancement of charge injection and transport in hybrid organic/inorganic light emitting devices

ZnO nanocrystals were synthesized by hydrolysis in methanol. X-ray diffraction and photoluminescence spectra confirm that good crystallized ZnO nanoparticles were formed. Utilizing those ZnO nanoparticles and poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV), light emitting devices with indium tin oxide (ITO)/poly(3,4-oxyethyleneoxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS)/ZnO:MDMO-PPV/Al and ITO/PEDOT:PSS/MDMO-PPV/Al structures were fabricated. Electroluminescence (EL) spectra reveal that EL yield of hybrid MDMO-PPV and ZnO nanocrystals devices increased greatly as compared with pristine MDMO-PPV devices. The current-voltage characteristics indicate that addition of ZnO nanocrystals can facilitate electrical injection and charge transport. The decreased energy barrier to electron injection is responsible for the increased efficiency of electron injection.     

A detector telescope with charge coupled devices for particle dosimetry in space

A telescopic device with charge coupled devices (CCDs) for particle dosimetry in space has been developed. Data on ionization events of energetic particles passing the CCDs are processed in an image analyzing system of a PC. As ‘Charged Particle Telescope’ (CHAPAT), the equipment was flown on the russian space station MIR during the EUROMIR mission in 1995. The response of the CCDs to various charged particles and methods for the discrimination of heavy particles in CCDs are discussed. First results of a correlation of temporal particles fluxes to the actual orbital parameters of MIR clearly identify passages through the South Atlantic Anomaly (SAA).     

A study of factors affecting the InSb c.w. spin-flip Raman laser

The behaviour of the c.w. spin-flip Raman laser is quantified by comparing its operation in the regimes of pump depletion and spin-saturation using InSb samples of different electron concentrations. The use of such a system for wide range spectroscopic applications, complementary to its narrow linewidth characteristic, is indicated.     

Superconductivity of polymers with charge injection doping

We show that conductivity measurements on sandwiches of a polymer between normal‐metal and superconducting‐metal electrodes can be interpreted in terms of intrinsic superconductivity due to injection of charge into the polymer.     

Effects of hysteresis and eddy currents in magnetostrictive harvesting devices

The paper tackles the analysis of the magnetostrictive energy harvesting phenomena by formulating a model where the hysteretic static characteristic of the material and eddy currents induced by Villari effect are taken into account. The study aims to analyze the main loss mechanisms involved in this kind of devices, highlighting the impact of the hysteretic material behavior with respect to the linear and non-linear memoryless approaches.     

质子辐照电荷耦合器件诱导电荷转移效率退化的实验分析

开展了电荷耦合器件（CCD）质子辐照损伤的实验研究. 分析了质子辐照CCD后电荷转移效率的退化规律,阐述了质子辐照诱导电荷转移效率退化的损伤机理,比较了不同能量质子对电荷转移效率的损伤程度. 通过开展辐射粒子输运理论计算,分析了不同能量质子对电荷转移效率损伤差异的原因. 关键词： 电荷耦合器件 质子 辐照效应 电荷转移效率