有机电致发光器件发光层中电场与载流子浓度分布的数值研究

以陷阱电荷限制传导理论为基础,用数值方法研究了单层有机电致发光器件发光层中电势、电场和载流子密度的空间分布.分析结果表明,电场强度在靠近两边电极的地方上升很快,而在中间区域几乎是线性地缓慢增大.大部分载流子分布在靠近两个电极的地方,只有少量分布在中间区域.在靠近注入电极的地方扩散电流大于漂移电流,而在其它区域漂移电流大于扩散电流.     

LDD结构参数对多晶硅薄膜晶体管热载流子退化的影响

基于Tsuprem4和Medici模拟软件,研究了LDD结构对多晶硅薄膜晶体管热载流子退化的影响.计算结果表明当栅氧层厚度tox=0.07 μm时,碰撞离化产生率和热电子注入电流峰值将达到最大,扩展区掺杂浓度增加,使沟道中横向电场和碰撞离化产生率的峰值分布区域向着栅电极的方向移动,即在应力作用下,热载流子退化的区域向着栅电极的方向漂移.     

InAs/GaAs量子点中间带太阳电池的理论研究与优化

基于InAs/GaAs量子点中间带太阳电池(QD-IBSC)结构和载流子漂移扩散理论建立了计算电流密度与静电势的数学模型,从理论上分析了量子点中间带太阳电池的电压电流特性,定量讨论了量子点层厚度、温度以及n型掺杂对电压电流特性的影响.模拟结果表明:在i层厚度取400 nm时转化效率达到最大值14.01％;温度会对量子点中间带太阳电池的电压电流特性产生影响,温度在300～350 K范围内,开路电压Voc随温度的升高而明显减小,短路电流Jsc几乎不变;对i区进行n型掺杂会抑制量子点层发挥作用.     

SAGCM-APD增益影响因子分析与优化

应用二维漂移扩散模型研究具有分立吸收层、渐变层、电荷层和倍增层结构(SAGCM)的InGaAsP-InP雪崩光电探测器(APD),仿真分析了不同电荷层、倍增层厚度和掺杂浓度对电场分布、电流响应及击穿电压的影响,特别是参数变量对增益计算模型的影响,载流子传输过程的时间依赖关系和倍增层中所处位置的影响,仿真结果表明:较高掺杂浓度和较薄电荷层结构可以改变器件内部的电场分布,进而提高增益值.当入射光波长为1.55μm,光功率为500 W/m2时,光电流响应量级在10-2A;阈值电压降低到10V以下,击穿电压为42.6V时,器件倍增增益值大于100.     

MLCC击穿原因浅析

从MLCC内部结构入手,分析了造成其电场畸变和电流分布不均匀的原因。运用有介质时的高斯定理,论证了在某些位置上非均匀电场强度要大于均匀电场强度。在MLCC内电极当中,处于最外边的上、下两个电极层所承受的电流相对较小,越靠近外电极,内电极层流过的电流越大。在此基础上,提出了在MLCC内部容易出现电压击穿和电流击穿的部位。     

台面尺寸对垂直腔面发射激光器电学特性的影响

采用求泊松方程、电流密度方程、载流子扩散方程以及有源层结压降方程自洽解的方法,计算了不同台面大小的台面结构垂直腔面发射激光器内部的电势分布和有源层中的注入电流密度、载流子浓度及结压降分布.结果表明,台面尺寸对垂直腔面发射激光器内部的电势分布和有源层中的注入电流密度、载流子浓度及结压降分布有重要影响.在一定的外加电压下,随着台面尺寸减小,有源层中心处的注入电流密度、载流子浓度和结压降急剧减小,垂直腔面发射激光器性能恶化.     

有机双层薄膜器件界面限制传导温度特性研究

通过对器件的温度特性的研究,能够使器件在合适的温度下保持稳定的工作状态.本文以Miller-Abrahams跳跃传导理论为基础,建立了有机-有机界面限制电流传导的电荷传输的解析模型.依据此模型分析了结构为“注入电极/有机层Ⅰ/有机层Ⅱ/收集电极”的双层薄膜器件在有机界面限制电流传导状态下的电流、电场和载流子分布与工作温度的变化关系.结果表明,在给定的工作电压下,温度升高时降落在层Ⅰ的电压升高,电场增强,而降落在层Ⅱ的电压降低,电场减弱,同时器件的电流增大.     

长基区晶体管的磁敏感效应

当n~+-i-n~+型晶体管的基区宽度大于载流子扩散长度时,在磁场中它的集电极电流具有很高的磁灵敏度.本文从输运基区载流子连续方程式出发导出了载流子在磁场中的分布,从而导出了集电极电流、电流增益α和β随磁场变化的关系式,并建立了磁灵敏度公式.本文将理论同锗长基区滋晶体管的实验曲线和数据进行了比较,其结果表明理论和实验曲线基本相符合.     

利用传输线模型的载流子倍增寄存器的频率特性研究

介绍了一种电荷载流子倍增寄存器(CCM)电极问隙的传输线模型,通过求解其波动方程得到了电荷载流子倍增寄存器电极间隙的电势分布及电场分布.模拟分析表明:电荷载流子倍增寄存器电极间隙的电势分布是与电荷载流子倍增寄存器工作频率相关的函数.电势分布沿信号电荷密度流方向衰减且电荷载流子倍增寄存器工作频率越高,电势衰减越快.电荷栽...     

LED电极结构优化设计与仿真计算

LED电极结构极大地影响着LED芯片的电流扩展能力,优化电极结构,能够缓解电流拥挤现象.讨论了正装LED结构和倒装LED结构的电流分布模型,并通过SimuLED软件研究了电极结构对LED电流扩展能力的影响.仿真结果表明:采用插指型电板结构极大提高了正装LED的电流扩展能力,电极下方插入电流阻挡层(CBL)后改变了芯片的电流分布状况,有利于光效的提升;而倒装LED的通孔式双层金属电极结构利用两层金属的互联作用,使n电极能够在整个芯片范围内均匀分布,进一步提高了电流扩展性能.     

Analysis of a transparent organic photoconductive sensor

The electro-optical performance of transparent photoconductive sensors based on stacks of organic layers is investigated. The photoconductive sensors are composed of interdigitated electrodes covered with a stack of two transparent organic compounds: a hole transport layer 1,3,5-tris[(3-methylphenyl)phenylamino]benzene (m-MTDAB) and an exciton generation layer 3,4,9,10-perylenetetracarboxylic bis-benzimidazole (PTCBI). The photocurrent through the device is measured as a function of the voltage across the electrodes for different illumination levels. Based on the measurements we can explain the working principle of the photoconductive sensor and compare the performance of four different stacks. In order to study the optical sensitivity in more detail, a photoconductive device with two parallel electrodes is manufactured and illuminated by a line-shaped laser beam that covers only a fraction of the gap between the electrodes. The current through the photoconductive sensor is measured as a function of the position of the local illumination for a set of voltages. The experimental results confirm that there is a high-field space charge region near the cathode.     

The role of local potential minima on charge transport in thin organic semiconductor layers

We have performed a systematic study of dependence of time-resolved photocurrent on the point of charge excitation within the organic semiconductor channel formed by two coplanar metal electrodes. The results confirm that spatial variation of electric field between the electrodes crucially determines transport of photogenerated charge carriers through the organic layer. Time-of-flight measurements of photocurrent demonstrate that the transit time of photogenerated charge carrier packets drifting between the two electrodes decreases with increasing travelling distance. Such counterintuitive result cannot be reconciled with the spatial distribution of electric field between coplanar electrodes, alone. It is also in contrast to expected role of space-charge screening of external electric field. Supported by Monte Carlo simulations of hopping transport in disordered organic semiconductor layer, we submit that the space-charge screens the external electric field and captures slower charge carriers from the photogenerated charge carrier packet. The remaining faster carriers, exhibit velocity distribution with significantly higher mean value and shorter transit time.     

Space charge and light generation in SrS:Ce thin filmelectroluminescent devices

Transient light and charge-voltage measurements on SrS and SrS:Ce thin film electroluminescent devices have been carried out with triangular voltage bursts after illumination. The observations indicate that the trailing edge emission is due to electrons which are emitted from the anodic interface as soon as the field there changes sign and recombine effectively with ionized Ce atoms. From charge-voltage measurements the space charge in the phosphor layer is estimated to be two times higher for the Ce doped sample. Due to this sample charge the field in the phosphor layer of the SrS:Ce devices decreases dramatically from the cathodic toward the anodic interface. If the field at the anodic interface is close to zero, efficient light emission will arise from recombination of electrons with ionized Ce atoms in this region     

三极FED分段复合衬底电极的特性和制作

结合丝网印刷技术、烘烤工艺和烧结工艺,采用印刷ZnO层和银浆层相结合的方案,进行了分段复合衬底电极的制作。该分段复合衬底电极能够降低无效的阴极电压降,增强三极场发射显示器的发光亮度并改善其发光均匀性,且制作成本低廉。分段复合衬底电极避免了过长过细衬底电极现象,促使碳纳米管提供更多电子,同时有效改善了碳纳米管的场发射均匀性。利用碳纳米管作为阴极材料,进行了三极场发射显示器的研制,并进行点阵图像显示,从而证实了这种分段复合衬底电极制作工艺的可行性。与普通银电极场发射显示器相比,分段复合衬底电极场发射显示器能够将开启场强从1.92 V/μm降低到1.81 V/μm,其最大场发射电流由1 332.5μA提高到2 137.8μA,具有典型的场致发射特性以及优良的图像发光均匀性。     

Space charge limited and emitter current limited injections in space charge region of semiconductors

If, in a space charge region of a semiconductor device, a unipolar drift current is a main component of the total current, an analogy with motion of electrons in vacuum exists. In the space charge limited emission, injection of minority carriers is limited by space charges, as in a punched-through p-n-p diode. On the other hand, in a transistor, minority carriers are injected into the depletion layer between the base and the collector, after diffusion in the neutral base region. This injection is limited by emitter current, and this mode of injection corresponds to a temperature limited emission in a vacuum tube. In this paper, equations of minority carrier impedances will be calculated in both these cases, and negative resistances can be expected at some transit angles. Then a generalized equation, which includes these two modes of injections as special cases, will be obtained. This generalized equation corresponds to the Llewellyn-Peterson equation of vacuum tubes, which include the space charge limited emission and the temperature limited emission as special cases.     

Photon-induced charge transfer and surface emission

Experimental measurements have been made of photon-induced charge transfer between plane-parallel electrodes. X-rays from a pulsed X-ray source were directed at near-normal incidence onto plane-parallel electrodes, and the current which flowed between the electrodes during the X-ray pulse was measured. Quantities obtained include bulk charge transfer in several dielectric materials; forward and reverse electron emission from Al, Cu, and Au surfaces; and secondary electron emission coefficients for these metals and selected dielectrics. Measured values for charge transfer and surface emission are compared with calculations.     

Microplasma effects in gallium arsenide epilayers and FETs

Breakdown of GaAs field-effect transistor (FET) structures is primarily a substrate effect beginning near the positive ohmic contact. The electric field across the space charge layer of the diode between the active layer and the surface of the substrate can exceed the avalanche breakdown value. The avalanche process is active at higher drain voltages, though still far from the burnout voltage. Microplasma effects were observed in addition to light emission and high noise power generation in gated and ungated FETs. The microplasma ignition should be originated from electron trapping in the epi-substrate interface. The back-side gating mechanism diminishes entirely in the avalanche breakdown region. Gunn oscillations were also observed but only in pulsed bias conditions.     

In-plane light emission of organic light-emitting transistors with bilayer structure using ambipolar semiconducting polymers

The concept of using an ambipolar bilayer semiconducting heterostructure in organic light-emitting transistors (OLETs) is introduced to provide a new approach to achieve surface emission. The properties of top-gate-type bilayer OLETs with ambipolar materials based on two types of fluorene-type polymers used as an emissive layer and an electron blocking layer are investigated. Line-shaped yellow–green emission occurs near a hole-injection electrode. When hole transport is dominant in the upper layer which acts as an electron blocking layer, and electrons are injected into the lower layer, an in-plane light-emitting pattern is observed. The measured in-plane emission zone confirms that both hole and electron transport are determined to occur mainly along the different organic layers between the source and drain electrodes, and an in-plane recombination zone of electrons and holes exists near the bilayer organic interface. This work is anticipated to be useful for the development of in-plane light-emitting transistors.     

All‐Carbon Nanotube‐Based Flexible Field‐Emission Devices: From Cathode to Anode

The fabrication of a flexible field‐emission device (FED) using single‐walled carbon nanotube (SWNT) network films as the conducting electrodes (anode and cathode) and thin multi‐walled CNT/TEOS hybrid films as the emitters is reported. P‐type doping with gold ions and passivation with tetraethylorthosilicate (TEOS) made the SWNT network film highly conductive and environmentally stable, and hence a good alternative to conventional indium tin oxide electrodes. CNT/TEOS hybrid emitters showed high current density, low turn‐on field, and long‐term emission stability, compared with CNT emitters; these characteristics can be attributed to the TEOS sol, acting both as a protective layer surrounding the nanotube tip, and as an adhesive layer enhancing the nanotube adhesion to the substrate. All‐CNT‐based flexible FEDs fabricated by this approach showed high flexibility in field emission characteristics and extremely bright electron emission patterns.     

Physical model of depletion and accumulation in quantum-wellinfrared photodetectors

Numerical work has shown that, at low operating temperatures or large incident photon fluxes, carriers deplete from the quantum wells near the emitter contact in a quantum-well infrared photodetector (QWIP). A physical model is developed in this work to describe, with closed-form analytical expressions, the accumulation and depletion of carriers in QWIPs. In QWIPs having the same growth sequence (layer widths and compositions) in each period, carrier depletion is found to occur only in one or two QWs near the emitter contact at the small applied biases for which the electron drift velocity is linear in the electric field. At intermediate applied biases for which the electron drift velocity is saturated, carrier depiction is found to be partial, uniform (throughout the depletion region), and abrupt, with the total charge in the depletion region fixed and with the depletion width increasing linearly with applied bias. At a large applied bias, carriers are found to be uniformly accumulated in the device. Carrier depletion or accumulation in QWIPs arises from the different dependences on the local electric field of the different physical mechanisms which are responsible for the carrier injection from the contacts (via thermionic emission or thermionic field assisted tunneling) and for the photoconduction process (via drift)