Microscopic view of charge injection in an organic semiconductor

We have measured the chemical potential and capacitance in a disordered organic semiconductor by electric force microscopy, following the electric field and interfacial charge density microscopically as the semiconductor undergoes a transition from Ohmic to space-charge limited conduction. Electric field and charge density at the metal-organic interface are inferred from the chemical potential and current. The charge density at this interface increases with electric field much faster than is predicted by the standard diffusion-limited thermionic emission theories.     

The shape of a drop in a constant electric field

The variation of the shape of a drop immersed in an immiscible liquid under the action of an electric field is calculated. The charge is transferred both by ohmic current through the interface and by the convective component over the interface. A solution quadratic in the parameter that is the ratio of the electric pressure to the capillary pressure is analyzed. Conditions where the drop transforms into a spheroid that is prolate or oblate along the electric field vector are found. An experimental study of the drop deformation by electric forces is carried out.     

有机半导体异质界面电荷传输解析模型研究

有机半导体多层薄膜器件的性质很大程度上由有机-有机界面的传输性质所决定，但是现有的关于有机-有机界面的分析模型很难适用于实际器件的模拟.以Miller-Abrahams跳跃传导理论为基础，充分考虑有机-有机界面和金属-有机界面性质的不同，建立了一个新的描述有机-有机异质界面电荷传输的解析模型.结果表明有机异质界面的载流子传输不仅取决于界面的肖特基势垒，而且还取决于界面附近两边的电场强度和载流子浓度.此模型可用于有机半导体多层薄膜器件的电流密度、电场分布和载流子浓度分布的自洽计算. 关键词： 有机半导体 界面 载流子传输     

半导体异质结构中的谷间电子转移效应

本文使用单带双谷理论研究了GaAs/AlGaAs异质结构中的谷间电子转移效应。计入每一异质结界面上的能带交错,谷间耦合和电场的贡献,导出了计算异质结构隧穿概率和隧道电流的公式。以GaAs/AlGaAs异质结构为例,算出不同结构、不同合金组分比及不同电压下的隧穿概率和隧道电流。讨论了异质结界面、势阱和势垒材料的能带结构以及外加电压对谷间电子转移效应的影响。算得的隧道电流同实验结果相符合,证实了这一理论在研究多能谷系统中的适用性。在此基础上进一步分析了这一谷间电子转移效应与熟知的Gunn效应间的区别,并讨论了它在半导体器件设计中的应用。 关键词：     

Injection and transport of electric charge in a metal/copolymer structure

The dynamical processes of the electric charge injection and transport from a metal electrode to the copolymer are investigated by using a nonadiabatic dynamic approach. The simulations are performed within the framework of an extended version of the one-dimensional Su-Schrieffer-Heeger (SSH) tight-binding model. It is found that the electric charge can be injected into the copolymer by increasing the applied voltage. For different structures of the copolymer, the critical voltage biases are different and the motion of the injected electric charge in the copolymer varies obviously. For the copolymer with a barrier-well-barrier configuration, the injected electric charge forms a wave packet due to the strong electron-lattice interaction in the barrier, then comes into the well and will be confined in it under a weak electric field. Under a medium electric field, the electric charge can go across the interface of two homopolymers and enter into the other potential barrier. For the copolymer with a well-barrier-well configuration, only under strong enough electric field can the electric charge transfer from the potential well into the barrier and ultimately reach a dynamic balance.     

铝-金刚石界面电子特性与界面肖特基势垒的杂化密度泛函理论HSE06的研究

宽带隙半导体金刚石具有突出的电学与热学特性,近年来,基于金刚石的高频大功率器件受到广泛关注,对于金属-金刚石肖特基结而言,具有较高的击穿电压和较小的串联电阻,所以金属-金刚石这种金半结具有非常好的发展前景.本文通过第一性原理方法去研究金属铝-金刚石界面电子特性与肖特基势垒的高度.界面附近原子轨道的投影态密度的计算表明:金属诱导带隙态会在金刚石一侧产生,并且具有典型的局域化特征,同时可以发现电子电荷转移使得Fermi能级在金刚石一侧有所提升.电子电荷在界面的重新分布促使界面形成新的化学键,使得金属铝-氢化金刚石形成稳定的金半结.特别地,我们通过计算平均静电势的方法得到金属铝-氢化金刚石界面的势垒高度为1.03 eV,该值与金属诱导带隙态唯像模型计算的结果非常接近,也与实验值符合得很好.本文的研究可为金属-金刚石肖特基结二极管的研究奠定理论基础,也可为金刚石基金半结大功率器件的研究提供理论参考.     

Random piezoelectric field in real [001]-oriented strain-relaxed semiconductor heterostructures

We work out a theory of piezoelectricity in an actual semiconductor heterostructure which is composed of a lattice-mismatched zinc-blende layer grown on a [001]-oriented substrate. In contrast to earlier theories, we predict a large density of fixed bulk piezoelectric charges, which are induced by strain fluctuations connected with interface roughness. The piezoelectric charges create a high electric field. The random piezoelectric field presents a conceptually new important scattering mechanism. The system of charge carriers in such a heterostructure becomes strongly disordered and includes generally both free electron-hole pairs near the interface and excitons far from it.     

Spectral photoresistive effect of the field in CdS crystals at low temperatures

The influence of the surface electric field on the low-temperature (T=77 K) photoconductivity spectra of CdS crystals in the region of exciton and interband transitions is experimentally studied by the field-effect method. The photoconductivity spectra of a semiconductor are numerically calculated in the framework of a model allowing for the dependence of the surface recombination rate of nonequilibrium charge carriers on the surface electric field. It is demonstrated that the surface electric field plays a decisive role in the formation of the fine spectral structure associated with the excitons. A correlation between the type of fine structure and the surface bending of the energy bands is revealed. It is shown that the surface electric field can be evaluated from the shape of the low-temperature photoconductivity spectrum of the semiconductor.     

Indirect electric field doping of the CuO2 planes of the cuprate NdBa2Cu3O7 superconductor

The mechanism of field-effect doping in the 123 high critical temperature superconductors (HTS) has been investigated by x-ray absorption spectroscopy in the presence of an electric field. We demonstrate that holes are created at the CuO chains of the charge reservoir and that field-effect doping of the CuO(2) planes occurs by charge transfer, from the chains to the planes, of a fraction of the overall induced holes. The electronic properties of the charge reservoir and of the dielectric-HTS interface determine the electric field doping of the CuO(2) planes.     

电场对1,4-苯二甲氰分子电输运特性的影响

用从头算理论和弹性散射格林函数的方法,计算电场作用下的1,4-苯二甲氰分子体系的电子结构及其电导和电流.结果表明:电场使体系在分子和电极间存在电荷转移和重新分布,分子与电极接触面附近出现电子积聚区和电子耗散区,从而产生附加电偶极子,对分子的电导和电流产生抑制.此外,对分子轨道能级和分子与电极的耦合系数的影响也比较明显,导致分子的伏-安特性在考虑电场作用前后有一定的差异.     

Contact electrohydrodynamic waves of free charge carriers at the interface of two semiconductor layers

It is shown that electrohydrodynamic waves similar to gravity waves at the interface of two liquids can propagate in a semiconductor structure composed of two semiconductor layers with different charge carrier densities and placed in a transverse electric field. The conditions for existence of such waves are specified. The linear and nonlinear modes of wave propagation are studied. State Technical University, Ulianovsk, Russia, Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 9, pp. 1164–11171, September, 1997.     

The influence of an electric field on the heat transfer rate during film boiling of stagnant fluids

This paper describes the influence of an electric field on the heat transfer rate during film boiling of stagnant fluids (pool boiling) on a horizontal surface. Modelling the influence of an electric field on the heat transfer during film boiling requires the knowledge of the equilibrium shape of the liquid-vapour interface. This equilibrium shape is calculated using an iterative solution technique. In each iteration step a fourth order Runge-Kutta technique is used to calculate the shape of the interface and a boundary element method is used to calculate the electric field. It is shown that the vapour bubbles formed on this interface become elongated in the presence of an electric field. This effect is accounted for in the existing heat transfer models in order to describe the influence of the electric field on the heat transfer coefficient during film boiling.     

The study of solid surfaces by electrochemical methods

The basic concepts of electrochemistry at the solid-electrolyte interface are discussed in this article with special emphasis on surface physical aspects. The electrochemical environment is shown to provide several unique experimental possibilities for the study of metal and semiconductor surfaces. Chemisorption processes, which are associated with charge transfer across the interface, can be studied with great accuracy, even when only submonolayer amounts are adsorbed. Semiconductor electrodes have recently received increasing attention and their fundamental properties, as well as selected experimental results, are described here. The optical reflectance of metal electrodes measures sensitively overlayers and the electric charge on the surface, both of which can easily be controlled by the voltage applied to the electrochemical cell. The final topic is photo-emission, which is usually associated with ultra high vacuum conditions but which, when studied at a metal-electrolyte contact, can be used to obtain complementary information, particularly at low excitation energies.     

Interface contact and modulated electronic properties by external vertical strains and electric fields in graphene/MoS2 heterostructure

Based to the first-principles calculations, we study the electronic properties of graphene/MoS₂ heterostructure by modulating the vertical strains and applying external electric field. Graphene/MoS₂ heterostructure is a van der Waals heterostructure (vdWH) with the interlayer spacing is 3.2 Å for the equilibrium state, and the contact property of the interface is n-type Schottky contact. The Schottky barrier height (SBH) changes with vertical strains which induces a change of charge transfer between graphene and MoS₂ layer. In addition, with strain or without strain, the applied positive electric field can effectively promote the charge transfer from graphene to MoS₂, while the negative electric field has the opposite effect. These findings support for the design of field effect transistors based on graphene vdWHs.     

二维MoSi2N4WSe2异质结的第一性原理研究

实验上新合成的MoSi2N4（MSN）由于其独特的七原子层结构和电子特性引起了人们的广泛关注。本文搭建了一种由二维MSN与二维WSe2（WS）垂直堆垛而成的二维MSN/WS异质结，其表现出直接间隙半导体和I型能带排列的特性，具有1.46 eV的带隙。在异质结界面处存在一个由电荷耗尽层MSN指向电荷积累层WS微弱的内建电场。最后，通过施加双轴应变对二维MSN/WS异质结进行调控。发现在正双轴应变的作用下，MSN/WS异质结保持了原来直接带隙半导体和I型能带排列特性；在负双轴应变作用下，MSN/WS异质结由原来的直接带隙半导体转变为间接带隙半导体，当施加的负双轴应变达到-6%与-8%时，I型能带排列转变为Ⅱ型能带排列。     

二硫化钼/石墨烯异质结的界面结合作用及其对带边电位影响的理论研究

采用基于色散修正的平面波超软赝势方法研究了二硫化钼/石墨烯异质结的界面结合作用及其对电荷分布和带边电位的影响.研究表明二硫化钼与石墨烯之间可以形成范德瓦耳斯力结合的稳定堆叠结构.通过能带结构计算,发现二硫化钼与石墨烯的耦合导致二硫化钼成为n型半导体,石墨烯转变成小带隙的p型体系.并通过电子密度差分图证实了界面内二硫化钼附近聚集负电荷,石墨烯附近聚集正电荷,界面内形成的内建电场可以抑制光生电子-空穴对的复合.石墨烯的引入可以调制二硫化钼的能带,使其导带底上移至-0.31 eV,提高了光生电子还原能力,有利于光催化还原反应.     

Novel high-voltage power device based on self-adaptive interface charge

This paper presents a novel high-voltage lateral double diffused metal--oxide semiconductor (LDMOS) with self-adaptive interface charge (SAC) layer and its physical model of the vertical interface electric field. The SAC can be self-adaptive to collect high concentration dynamic inversion holes, which effectively enhance the electric field of dielectric buried layer (E_I) and increase breakdown voltage (BV). The BV and E_I of SAC LDMOS increase to 612 V and 600 V/μm from 204 V and 90.7 V/μm of the conventional silicon-on-insulator, respectively. Moreover, enhancement factors of η which present the enhanced ability of interface charge on E_I are defined and analysed.     

Space charge behavior and its modified electric field in the cross-linked polyethylene under applied voltage DC and different temperatures

In this paper, space charge behavior in dielectric material and the capacitive charge at an electrode-dielectric interface, at room temperature under an applied electric field, has been investigated. This was done for a single sample and for a combination of the sample and a non-stressed sample using the pulsed electro-acoustic (PEA) method. A negative charge injected at the dielectric interface under an electric field (polarization) and high temperatures was focused on. It was found that negative charge injection takes place under all the test conditions, and this charge can be affected by the electric field and the temperature.     

STM针尖和外电场在Si(111)-7×7表面单原子操纵中的作用

利用第一性原理的离散变分局域密度泛函方法,采用团簇模型（Si₃₄H₃₆-W₁₁)来模拟STM操纵Si(111)-7×7表面顶角吸附原子的过程．通过分析在进行原子操纵过程中体系的能量与电子云密度分布来研究针尖和外电场的作用．结果表明,当针尖与样品间距离较近时,利用两者间有较强的相互作用,能有效地降低脱出能的能垒高度．外电场对体系脱出能的影响与其大小及极性有关,当样品上所加正偏压增强时,脱出能曲线高度单调下降,而外电场极性为负时,反而稍有增高．仅考虑针尖和样品之间的静态电子相互作用及静电场的作用,尚不能使被操纵原子脱离样品表面．最后讨论了在Si(111)-7×7表面上进行原子操纵的其他机理.     

Electric-field and interface effects on the orientation of Jahn-Teller vacancy distortions in semiconductors

Energy variation of various Jahn-Teller vacancy configurations in thin near-surface layers of a semiconductor is considered. The calculations are made within a model in which each dangling bond near a vacancy is described by the wave function of an electron localized at a defect with a zero-range potential. The Jahn-Teller stabilization energy was assumed to be much smaller than the crystal-field splitting but substantially larger than the energy variations introduced by other perturbations. It is shown that vacancy alignment in semiconductor layers with thickness ?100 Å at liquid-nitrogen temperatures and lower can be most effectively caused by the electric field which can exist in such layers due to a surface-state charge. The direct effect of the interface on both the electronic and nuclear energies of various configurations is weak and can become manifest only in layers less than 10 Å thick at liquidhelium temperature.