ZrNCl薄层中基于固体离子导体场效应管的电场诱导的超导电性

场效应晶体管(FET)可以通过电场可逆调控材料的载流子浓度,是一种控制二维材料系统电学性质的有效方法.最近,作者实验室发明了一种新的场效应晶体管器件,它利用固体离子导体(SIC)作为栅介质,通过电场驱动锂离子进出样品来调控样品的载流子浓度,从而控制样品的物理性质和相变.在本论文中,作者利用这种新型的固体离子导体基场效应管器件(SIC-FET)成功地调控了ZrNCl薄层的电学性质.通过施加电场,将固体锂离子导体中的锂离子插入ZrNCl薄层样品中,实现了样品从绝缘体到超导体的转变,最佳超导电性的中点临界温度约为15.1K.实验结果表明,固体离子导体基场效应管器件具有在层状材料中引入载流子的优异性能,该器件将是寻找新的超导体和其他新奇电子相的有效途径.     

固体离子学概述

 固体离子学是研究固体中离子行为及其相关应用的科学.它是在七十年代才兴起的新学科。内容包括快离子导体(又叫固体电解质),混合导体(又称电极材料)和它们的应用。它是物理、化学、材料、器件的交叉学科,因而引起广泛领域的科学家和工程师的兴趣和关注.自然界的固态材料依据其导电能力来分类可分为导体、半导体和绝缘体.在不特别指明电荷载流子的情况下,这种分类都是相对于电子(或空穴)的导电能力而言的.     

HgCdTe异质结接点光导体

本文描述了异质结接点的新型光电导体器件结构,这种结构在普通带隙的光导体与金属接点之间接合了一个较高带隙的HgCdTe合金。异质结接点光导体器件的理论分析证明能有效地消除载流子清扫效应;根据计算结果断定,由于消除了响应度的“饱和”效应,故可以大大增加响应度。现已制成了异质结接点器件,用几种方法实验,结果验证了这种理论,在80K时,测得的响应度在30V/cm时约为45×10~4V/W,在125V/cm时超过15×10~5V/W。     

考虑空间电荷层效应的氧离子导体电解质内载流子传输特性

晶界或异质界面诱发的空间电荷层(space charge layer,SCL)效应,被认为是氧离子导体电解质内界面附近区域载流子传输特性显著区别于体相区域的关键原因之一.现有研究多采用Poisson-Boltzmann(PB)方程预测SCL效应的影响规律,但其基于载流子电化学平衡假设,无法用于载流子存在宏观运动的工况,极大限制了相关传输机理研究.本文耦合Poisson方程和载流子质量守恒方程,建立了适用于载流子具有宏观运动时氧离子导体内载流子传输过程的模型,推导了控制SCL效应的关键无量纲参数.聚焦固体氧化物燃料电池中常用的AO2-M2O3氧离子导体电解质,对比研究了传统PB方程和本文建立的Poisson-载流子质量守恒耦合方程的预测结果可靠性.进一步采用耦合模型深入分析了考虑SCL效应时氧离子导体内部氧空位传输机理,发现导体界面电流密度增大导致SCL电阻先减小后增大.增大无量纲Debye长度(表征空间电荷层厚度与导体厚度的比值)可显著增大SCL电阻.当驱动氧空位移动的过电势与热势数量级相当时,增大无量纲电势(表征过电势与热势的比值)导致SCL电阻增大;当过电势远小于热势时,改变无量纲电势对氧空位传输过程几乎无影响.本文研究结论可为通过合理设计晶界或异质界面以改善氧离子导体内载流子传输能力及最终提高相关电化学器件性能提供理论依据.     

GaN基异质结缓冲层漏电分析

通过对GaN基异质结材料C-V特性中耗尽电容的比较,得出AlGaN/GaN异质结缓冲层漏电与成核层的关系.实验结果表明,基于蓝宝石衬底低温GaN成核层和SiC衬底高温AlN成核层的异质结材料比基于蓝宝石衬底低温AlN成核层异质结材料漏电小、背景载流子浓度低.深入分析发现,基于薄成核层的异质结材料在近衬底的GaN缓冲层中具有高浓度的n型GaN导电层,而基于厚成核层的异质结材料的GaN缓冲层则呈高阻特性.GaN缓冲层中的n型导电层是导致器件漏电主要因素之一,适当提高成核层的质量和厚度可有效降低GaN缓冲层的背景载流子浓度,提高GaN缓冲层的高阻特性,抑制缓冲层漏电. 关键词： AlGaN/GaN异质结 GaN缓冲层 漏电 成核层     

类石墨烯硼-磷单层材料的电子与光学性能的第一性原理计算研究

基于第一性原理计算,对硼-磷单层材料的电子结构和光学性质进行系统地理论研究. 全局结构搜索和第一性原理分子动力学模拟现实二维硼-磷单层材料能量最低的结构与石墨烯类似,具有很高的稳定性. 类石墨烯二维硼-磷单层是直接带隙半导体,带隙宽度1.37 eV,其带隙宽度随层数增加而减少. 硼-磷单层的带隙宽度受外界应力影响.硼-磷单层的载流子迁移率达到106 cm2/V. MoS2/BP二维异质结可用于光电器件,其理论光电转换效率为17.7%?19.7%. 表明类石墨烯硼-磷二维材料在纳米电子器件与光电子器件的潜在应用价值.     

平面异质结有机-无机杂化钙钛矿太阳电池研究进展

高效低成本太阳电池的研发是太阳能光伏技术大规模推广应用的关键. 近年来兴起的有机- 无机杂化钙钛矿(以下简称钙钛矿)太阳电池因具有光电能量转换效率高、制备工艺简单等优点, 引起了学术界和产业界的广泛关注, 具有广阔的发展前景. 其中平面异质结钙钛矿太阳电池因具有结构简单, 可低温制备等诸多优点, 成为目前研究的一个重要方向. 平面异质结钙钛矿太阳电池分为n-i-p型和p-i-n型两种结构. 其中钙钛矿分别与电子传输层和空穴传输层形成两个界面, 在这两个界面上实现电子和空穴的快速分离. 电子传输层和空穴传输层分别为电子和空穴提供了独立的输运通道. 平面异质结结构有利于钙钛矿太阳电池中电子和空穴的分离、传输和收集. 此外, 该结构不需要高温烧结的多孔结构氧化物骨架, 扩大了电子和空穴传输材料的选择范围. 可以根据钙钛矿材料的能带分布及载流子传输特性, 来选择能级和载流子传输速率更为匹配的传输材料. 本文对钙钛矿的材料特性, 平面异质结结构的由来及发展进行了简要的概述. 其中重点介绍了平面异质结钙钛矿太阳电池的结构特征、工作机理、钙钛矿/电荷传输层的界面特性, 以及电池性能的优化, 包括钙钛矿薄膜制备、空穴和电子传输层的优化等. 最后对钙钛矿电池的发展前景及存在问题进行了阐述, 为今后高效、稳定钙钛矿太阳电池的研究提供参考.     

基于面跳跃方法的半导体纳米材料从头算非绝热分子动力学研究

在光电子学应用中,器件性能主要取决于半导体纳米材料中的光生载流子动力学过程. 但是,受反应速率、材料表面积、材料组成等多种因素影响,描述其中的动力学过程非常具有挑战性. 模拟光生载流子动力学过程可以通过绝热分子动力学方法实现,即求解包含非绝热耦合项的含时薛定谔方程. 在众多绝热分子动力学方法中,面跳跃方法出色地平衡了计算精度和计算成本,因而成为描述半导体纳米材料中不同非绝热过程间竞争的有力工具,已被用来模拟材料中的超快动力学过程和其他复杂效应,如Janus过渡金属二硫族化合物范德华异质结中的电荷分离. 本综述通过介绍该领域代表性的理论及实验工作,阐述了光生载流子对半导体纳米材料性能的重要影响,以及面跳跃方法在描述其动力学行为中的重要作用. 由于日趋复杂的材料体系对理论工作提出了巨大的挑战,本综述重点介绍了最近用于模拟这些复杂材料的一些开创性的新方法,包括高精度的电子结构方法和与之相结合的绝热分子动力学方法.     

双异质结结构的双极型有机薄膜晶体管的研制

制备了基于F₁₆CuPc和CuPc的双异质结结构的双极型有机薄膜晶体管。该器件的载流子迁移率是相同工艺制备的F₁₆CuPc和CuPc双层单异质结有机薄膜晶体管器件的4~5倍。同时,该双异质结结构还能调整载流子的阈值电压,减少双层结构对薄膜厚度等工艺条件的苛刻要求。这种双异质结结构为提升双极型有机薄膜晶体管器件的性能提供了一种有效方法。     

半导体器件

一、引 言 所有半导体器件就其用途来说有两类.一类是用于研究某些基本的物理参量.例如金属-绝缘体-半导体二极管,其主要用途是研究半导体表面的性质和钝化技术的性质及效果.又如热电子晶体管可用于研究热电子寿命和载流子通过薄膜时的输运性质.另一类则是应用于实际的电子线路.在生产实践和科学实验中这一类是主要的、大量的.我们可以把半导体器件按其作用性质归为如下四大类.1.双极型器件 这一类器件的主要特点是有两种不同极性的载流子(电子和空穴)参与电荷的输运过程.器件中含有一个或多个p—n结.器件的一些特性主要由少数载流子的输运…     

Interfaces in ionic devices

The technology of Ionics is based on the availability of materials with fast ion transport. Individual materials are, however, meaningless from a practical point of view; all applications require combinations of materials with appropriate ionic and electronic properties. This situation is similar to Electronics which requires combinations of semi-conducting or metallic conducting materials with differences in the chemical potentials of the electrons. The technology of Ionics requires interfaces between ionic and electronic conductors which generate strong electrical fields or allow to modify the field by the application of external voltages. Ions and electrons equilibrate both at these “ionic junctions”. While semi-conductor junctions have commonly a width in the μm-range, the space charge region is several orders of magnitude smaller in the case of ionic junctions, i.e. in the nm or even sub-nm-range. The interfaces have to be chemically stable for the lifetime of the device which is difficult to achieve in view of the commonly large number of components present in both phases and the existence of mobile species with sometimes large variations in the activity of the electroactive component. Furthermore, the kinetics of transfer of ions across the interface has to be fast to allow high current densities which are required in many cases. In addition, two such interfaces are required to convert the electronic current into an ionic one and again back into an electronic current at the opposite side of the electrolyte. The development of ionic devices depends to the strongest extent on the engineering of appropriate interfaces. Examples of the role and engineering of interfaces will be presented for applicationes such as chemical sensors, electrochromic devices, fuel cells, batteries and photogalvanic solar cells.     

Engineering of solid state ionic devices

Solid state ionic devices such as high performance batteries, fuel and electrolysis cells, electrochromic devices, chemical sensors, thermoelectric converters or photogalvanic solar cells are of tremendous practical interest in view of our energy and environmental needs. The challenges are the achievement of higher energy and power densities, longer lifetimes, cheaper materials, lower cost, improved sensitivity and higher stability. The engineering of new devices is based on the better fundamental understanding of materials for galvanic cells and their interaction in order to approach solutions more systematically than in the past. The fundamental aspects of the generation of voltages and electrical currents are compiled and analysed in view of the materials requirements. Conflicts exist in forming chemically stable interfaces of functionally different electrolyte and electrode materials, achieving simultaneously high energy and power densities in view of low conductivities of chemically stable materials, fast chemical diffusion in electrodes which should have a wide range of non-stoichiometry for delivering and absorbing the mobile ionic species, practical problems of using less expensive polycrystalline materials which have high intergranular resistances and finally reaching both ionic and electronic equilibria at the electrolyte - electrode interfaces at low temperatures. The engineering of new or improved solid state ionic devices is commonly based on individual materials considerations and their interaction in galvanic cells. Simultaneously high ionic conductivity and chemical stability may be reached by designing structures of poly-ions of the non-conducting components with the conducting species in-between. The chemical stability may be based on kinetic restrictions for sufficiently long periods of time of operation of the devices. Electrodes should not be made of metallic conductors but of electronic semi-conductors with fast enhancement of the diffusion of ions by internal electrical fields. Device considerations are based on the development of single element arrangements (SEAs) which incorporate the electrodes into the electrolyte in the case of fuel and electrolysis cells. The electronic conductivity is generated by the applied gas partial pressures or the applied voltage. The same simplification may be applied for electrochromic systems which consist of a single active layer instead of the conventional three galvanic cell materials. A new design of active chemical sensors probing the environment by the magnitude of the applied voltage or current may overcome the limitations of cross sensitivities and interfacial reactions which allows the simultaneous detection of several species by a single galvanic cell. The paper has been prepared for presentation at the International Conference on Ionic Devices — 2003, Anna University, Nov. 28–30, 2003, Chennai, India.     

Electrochromism by polarization of semiconducting ionic materials

Electrochromic effects are observed by employing a single mixed ionic and electronic conducting layer in-between two transparent electronic leads. Besides the simplicity of the arrangement, the advantage is the displacement of ions only within one phase rather than across phase boundaries as required by conventional devices. The applied voltage controls the compositions at the two interfaces according to Nernst's law independent of ions being majority or minority charge carriers. Appropriate materials are intrinsic conductors in the unpolarized transparent state which become n-type and p-type conducting at the negative and positive electrode side, respectively. Several materials have been investigated, such as lithiated tungsten oxide and lithium/tantalum co-doped tungsten oxide. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 September 1994.     

Oxygen removal and level control with zirconia — Yttria membrane cells

Oxygen-ion conducting ceramic membrane materials (pure ionic or mixed ionic / electronic conductors) allow selective transport of oxygen in the form of ionic flux at high temperatures and can be used for the production of high purity oxygen. Such materials are also more appropriate for gas purification (residual oxygen removal) and control of oxygen levels in a gas stream to produce gases with known oxygen partial pressure. In this paper, operation and limitations of laboratory scale prototypes constructed from tubular zirconia — yttria membranes have been described for the removal of oxygen from air and low oxygen containing gases to produce oxygen-free gas streams and generation of calibration gases with pre-defined levels of oxygen.     

Surfaces and interfaces in polymer-based electronics

Research on electronics applications such as light-emitting devices for flat-panel displays, transistors, sensors and even solid state lasers based on conducting polymers is presently under way and in some cases has reached the stage of prototype production. The mechanisms for charge injection and conduction in these materials are being studied, as are the physics of luminescence and its quenching. Lately, research into controlling film morphology through self-organizing techniques also has gained interest. Though the present interest in conducting polymers mainly concerns the pristine semiconducting state, doped conducting polymers are also studied for potential use in many applications.

In this paper, we present an overview of some of the central issues in surface and interface science in the field, as well as provide our view on what may lie ahead in the future. Specifically, the importance of metal/polymer, polymer/metal and polymer/polymer interfaces is addressed. We illustrate these using polymer-based light-emitting devices, though the same type of issues appear in other polymer-based applications such as transistors and solar cells.     

Molecular dynamics simulations of oxide memristors: thermal effects

We have extended our recent molecular-dynamic simulations of memristors to include the effect of thermal inhomogeneities on mobile ionic species appearing during operation of the device. Simulations show a competition between an attractive short-ranged interaction between oxygen vacancies and an enhanced local temperature in creating/destroying the conducting oxygen channels. Such a competition would strongly affect the performance of the memristive devices.     

Ionics—a key technology for our energy and environmental needs on the rise

Ionics is a key technology for storing, converting and using energy efficiently as well as protecting the environment. Major progress has been achieved in recent years in the understanding and development of individual materials components needed for ionic devices. It should be emphasized that only combinations of materials are eventually important and at least four interfaces exist with electronic and ionic junctions. The electrical fields exist over distances in the atomic range. Examples are given of recent successful developments of practically useful solids for lithium and oxide ion conduction in combination with appropriate electrodes. In addition, recent approaches to the design of ionic devices are described, notably the SEA concept for generating voltages in fuel cells and the coloration of single phase electrochromic materials. In order to overcome the tremendous problems in developing wide spread commercial applications, it is necessary to intensify our efforts in fundamental materials research drastically.     

Magnonic circuits and crystals

In the frame of the long-wavelength Heisenberg model, a simple magnonic mono-mode circuit is designed to obtain transmission stop (pass) bands where the propagation of spin waves is forbidden (allowed). This simple device is composed of an infinite one-dimensional monomode waveguide (the backbone) along which side resonators (symmetric or asymmetric loops) are grafted. These circuits are usually mono-mode when the lateral dimensions of the conducting wires are small as compared to the magnon wavelength. Their production utilizes the most advanced surface technologies and represents one of the most important challenges for the next decade. In all these circuits, the interfaces between the different wires out of which the circuits are made, play a fundamental role. All such circuits exhibit a variety of interference effects in their transport properties. Emphasis in this review article is placed on the network creations, which include stubs or resonators, closed symmetric or asymmetric loops and interconnecting branched networks. In other words, a fundamental understanding of nanoscaled materials has become an important challenge for any technical applications. For magnetic nanoparticles, the investigations are in particular stimulated by the magnetic storage devices. Then we present a theory of the magnon propagation in a quasi-one-dimensional resonant structure, composed of one nanometric magnetic cluster chain and adsorbed clusters near the chain. Results for the transmission and reflection properties of such circuits (nanometric networks) are discussed, as a function of the frequency of the excitations and the physical or geometrical properties of the circuits.In the last part of this report, we review magnonic crystals. These man-conceived materials should be useful for many applications and, in particular, for designing the mono-mode circuits reviewed in the first part of this paper.These magnonic materials and circuits may have uses for the design of integrated devices such as narrow-frequency optical or microwave filters, high-speed switches, multiplexers, storage devices, ….     

Fast divalent ion conduction—Ion ordering in β AND β″ alumina (Sr2+, Cd2+, Pb2+)

We have prepared single crystals of divalent ion rich β alumina and β″ alumina (Cd²⁺, Sr²⁺, Pb²⁺) from sodium compounds by ion exchange. These compounds generally exhibit a similar composition (~0.83 M²⁺ per unit in the conducting plane) and the same compensation mechanism for the non-stoichiometry (Mg²⁺). X-ray studies (conventional structure determination and diffuse scattering) have been performed on these materials in order to establish the relationship between the structural and electrical characteristics. For the conducting ion organization, three typical cases have been displayed: a pure 2D local order when ions are localized in a quasi perfect conducting plane; a 3D local order when ions are localized in a conduction slab (ionic polarization of the host lattice); a 3D long-range order when ions are in-plane and out-plane on-centered from the theoretical position (ionic polarization of the host lattice and electronic polarization of the divalent ion).