硅纳米线纳米器件的研究进展

硅纳米线作为一类重要的一维半导体纳米材料,在纳米器件方面具有很好的应用前景,可以用于高性能场效应晶体管、单电子探测器和场发射显示器件等纳米器件的制备.介绍了近两年来硅纳米线作为检测细胞、葡萄糖、过氧化氢、牛类血清蛋白和DNA杂交方面的纳米传感器、纳米晶体管、光电探测器等纳米器件的最新进展,并对其研究前景做了展望.     

金属/氮化物肖特基势垒和欧姆接触研究进展

金属 /氮化物肖特基势垒和欧姆接触是蓝紫光光学器件及高温大功率电子器件中的关键工艺。氮化物半导体是一种极性材料 ,表面态密度较低 ,费米能级钉扎效应较弱 ,表面处理能显著影响接触特性。样品表面的沾污和氧化层也会使接触特性显著退化。宽禁带材料的杂质离化能高 ,重掺杂比较困难。深能级陷阱对载流子的俘获效应很强。这些因素都增加了接触的制作难度 ,促使人们寻求新的方案来改进接触特性。文中从金属 /半导体接触的物理模型出发来综述肖特基势垒和欧姆接触的研究进展 ,希望能给器件研究者提供新的思路。     

Progress in ZnO materials and devices

ZnO is a wide-band-gap semiconductor material that is now being developed for many applications, including ultraviolet (UV) light-emitting diodes, UV photodetectors, transparent thin-film transistors, and gas sensors. It can be grown as boules, as thin films, or as nanostructures of many types and shapes. However, as with any useful semiconductor material, its electrical and optical properties are controlled by impurities and defects. Here, we consider various important donor-type impurities, such as H, Al, Ga, and In, and acceptor-type impurities, such as N, P, As, and Sb. We also examine the effects of a few common point defects, including Zn interstitials, Zn vacancies, O vacancies, and complexes of each. The main experimental techniques of interest here include temperature-dependent Hall-effect and low-temperature photoluminescence measurements, because they alone can provide donor and acceptor concentrations and donor energies. The important topic of p-type ZnO is also considered in some detail.     

Catalytically Doped Semiconductors for Chemical Gas Sensing: Aerogel‐Like Aluminum‐Containing Zinc Oxide Materials Prepared in the Gas Phase

Atmospheric contamination with organic compounds is undesired in industry and in society because of odor nuisance or potential toxicity. Resistive gas sensors made of semiconducting metal oxides are effective in the detection of gases even at low concentration. Major drawbacks are low selectivity and missing sensitivity toward a targeted compound. Acetaldehyde is selected due to its high relevance in chemical industry and its toxic character. Considering the similarity between gas‐sensing and heterogeneous catalysis (surface reactions, activity, selectivity), it is tempting to transfer concepts. A question of importance is how doping and the resulting change in electronic properties of a metal‐oxide support with semiconducting properties alters reactivity of the surfaces and the functionality in gas‐sensing and in heterogeneous catalysis. A gas‐phase synthesis method is employed for aerogel‐like zinc oxide materials with a defined content of aluminum (n‐doping), which were then used for the assembly of gas sensors. It is shown that only Al‐doped ZnO represents an effective sensor material that is sensitive down to very low concentrations (<350 ppb). The advance in properties relates to a catalytic effect for the doped semiconductor nanomaterial.     

Propagation Properties of a Modified Slot Surface Plasmonic Waveguide

In this paper, we present a modified slot surface plasmonic waveguide formed by metallic rod, core dielectric layer, and metallic film on the substrate. Using the finite-difference frequency-domain method, modal field distribution are analyzed firstly. Results show that the fundamental mode could be well confined in the space between the metal rod and the metal film. The dependence of modal field distribution, effective index, and propagation length of the fundamental plasmonic mode without gain on dielectric constant of the core layer, geometrical parameters, and working wavelengths are analyzed and discussed. A kind of available gain dielectric medium was used for the core dielectric layer to extend the propagation length. Results show that the propagation length can be extended observably with the help of the gain dielectric medium. Finally, effect of the thickness of the core dielectric layer on modal field distribution, effective index, and propagation length are analyzed and discussed. Since the modal field distribution, effective index, and propagation length can be controlled by adjusting the geometrical parameters, dielectric constant and gain of the core layer and working wavelengths of the waveguide, this kind of surface plasmonic waveguide can be applied to the field of photonic device integration and sensors.      

Bulk degradation of GaP red LEDs

The external quantum efficiency of GaP red light-emitting diodes (LEDs) degrades under forward-biased operation. The degradation is a complex phenomenon which in the long run is dominated by changes in the bulk semiconductor. This paper is restricted to the discussion of bulk degradation. The symptoms of the degradation are: 1) for a given forward current, the activation energy of the degradation is 0.5-0.8 eV and 2) for a fixed forward voltage, the light output is virtually unchanged while the forward current increases. The nonradiative excess current responsible for the degradation is probably a tunneling current. The introduction of metallic impurities such as copper into the semiconductor material does not appreciably change the initial quantum efficiency of the device. On the other hand, it shortens the lifetime of the device by several orders of magnitude under forward-biased operation. The symptoms of the degradation for the copper-contaminated devices are identical to those of the noncontaminated devices including the activation energy of the degradation. It is inferred therefore that fast moving impurities such as copper are the major cause of the bulk degradation. Liquid gallium is a known getter for metallic impurities such as copper. For junctions grown in the liquid phase epitaxy (LPE) process using high-purity gallium, the longer life can be attained by the careful elimination of metallic impurities during material growth and device processing.     

Zinc Oxide Nanoparticles with Defects

Zinc oxide in the form of nanoscale materials can be regarded as one of the most important semiconductor oxides at present. However, the question of how chemical defects influence the properties of nanoscale zinc oxide materials has seldom been addressed. In this paper, we report on the introduction of defects into nanoscale ZnO, their comprehensive analysis using a combination of techniques (powder X‐ray diffraction (PXRD), X‐ray absorption spectroscopy/extended X‐ray absorption fine structure (XAS/EXAFS), electron paramagnetic resonance (EPR), magic‐angle spinning nuclear magnetic resonance (MAS‐NMR), Fourier‐transform infrared (FTIR), UV‐vis, and photoluminescence (PL) spectroscopies coupled with ab‐initio calculations), and the investigation of correlations between the different types of defects. It is seen that defect‐rich zinc oxide can be obtained under kinetically controlled conditions of ZnO formation. This is realized by the thermolysis of molecular, organometallic precursors in which ZnO is pre‐organized on a molecular scale. It is seen that these precursors form ZnO at low temperatures far from thermodynamic equilibrium. The resulting nanocrystalline ZnO is rich in defects. Depending on conditions, ZnO of high microstructural strain, high content of oxygen vacancies, and particular content of heteroatom impurities can be obtained. It is shown how the mentioned defects influence the electronic properties of the semiconductor nanoparticles.     

Growth and Device Application of CdSe Nanostructures

Inorganic semiconductor nanostructures have attracted increasing interest in recent years because of their distinguishable role in fundamental studies and technical applications, mainly due to their size‐ and shape‐dependent properties and flexible processing methods. The use of such nanostructures in optic, optoelectric, and piezoelectric prospects is expected to play a crucial role in future nanoscale devices. Cadmium selenide (CdSe), a well‐known direct bandgap II‐VI semiconductor in which the bandgap favors absorption over a wide range of the visible spectrum, has been a promising material for applications in such fields as photodetectors, field‐effect transistors (FETs), field emitters, solar cells, light‐emitting diodes (LEDs), memory devices, biosensors, and biomedical imaging. The research on CdSe nanostructures has made remarkable progress in the last few years. The research activities on CdSe nanostructures including various methods for the synthesis of CdSe nanostructures and the unique properties and device applications of these nanostructures are reviewed. Potential future directions of this research area are also highlighted.     

Two‐Dimensional Nanostructured Materials for Gas Sensing

Two‐dimensional (2D) nanostructures are highly attractive for fabricating nanodevices due to their high surface‐to‐volume ratio and good compatibility with device design. In recent years 2D nanostructures of various materials including metal oxides, graphene, metal dichalcogenides, phosphorene, BN and MXenes, have demonstrated significant potential for gas sensors. This review aims to provide the most recent advancements in utilization of various 2D nanomaterials for gas sensing. The common methods for the preparation of 2D nanostructures are briefly summarized first. The focus is then placed on the sensing performances provided by devices integrating 2D nanostructures. Strategies for optimizing the sensing features are also discussed. By combining both the experimental results and the theoretical studies available, structure‐properties correlations are discussed. The conclusion gives some perspectives on the open challenges and future prospects for engineering advanced 2D nanostructures for high‐performance gas sensors devices.     

All‐Metallic Vertical Transistors Based on Stacked Dirac Materials

It is an ongoing pursuit to use metal as a channel material in a field effect transistor. All metallic transistor can be fabricated from pristine semimetallic Dirac materials (such as graphene, silicene, and germanene), but the on/off current ratio is very low. In a vertical heterostructure composed by two Dirac materials, the Dirac cones of the two materials survive the weak interlayer van der Waals interaction based on density functional theory method, and electron transport from the Dirac cone of one material to the one of the other material is therefore forbidden without assistance of phonon because of momentum mismatch. First‐principles quantum transport simulations of the all‐metallic vertical Dirac material heterostructure devices confirm the existence of a transport gap of over 0.4 eV, accompanied by a switching ratio of over 10⁴. Such a striking behavior is robust against the relative rotation between the two Dirac materials and can be extended to twisted bilayer graphene. Therefore, all‐metallic junction can be a semiconductor and novel avenue is opened up for Dirac material vertical structures in high‐performance devices without opening their band gaps.     

脉冲激光沉积法制备ZnO基薄膜研究进展

作为一种新型的Ⅱ-Ⅵ半导体材料,ZnO具有优良的光学和电学性能,在紫外光发射器件、自旋功能器件、气体探测器、表面声波器件等领域有着广阔的应用前景.首先介绍了ZnO材料和脉冲激光溅射法的一些相关内容,然后从材料制备角度着重阐述了目前利用脉冲激光沉积法(PLD)制备ZnO基薄膜的若干重要研究方向,例如p型掺杂、p-n结的制备、Mg掺杂、Cd掺杂和磁性离子掺杂等.     

二维半导体光电性质与器件研究进展简述

二维半导体材料,如过渡金属硫族化合物,以其在光电器件方面展现出的独特性能与巨大潜力,成为后摩尔时代有极大发展前景的新半导体材料.二维材料具有独特的光电性质,如直接带隙的电子结构,谷自旋电子学特性,强激子效应等,而利用以上性质,此类材料可用于光探测器、场效应晶体管、高效微纳传感器、光电子电路等微纳光电器件中.因此,以过渡金属硫族化合物为代表的二维半导体材料无论在基础科学与未来应用方面,都是重要的备选材料.     

The Role of Hierarchical Morphologies in the Superior Gas Sensing Performance of CuO‐Based Chemiresistors

The development of gas sensors with innovative designs and advanced functional materials has attracted considerable scientific interest given their potential for addressing important technological challenges. This work presents new insight towards the development of high‐performance p‐type semiconductor gas sensors. Gas sensor test devices, based on copper (II) oxide (CuO) with innovative and unique designs (urchin‐like, fiber‐like, and nanorods), are prepared by a microwave‐assisted synthesis method. The crystalline composition, surface area, porosity, and morphological characteristics are studied by X‐ray powder diffraction, nitrogen adsorption isotherms, field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy. Gas sensor measurements, performed simultaneously on multiple samples, show that morphology can have a substantial influence on gas sensor performance. An assembly of urchin‐like structures is found to be most effective for hydrogen detection in the range of parts‐per‐million at 200 °C with 300‐fold larger response than the previously best reported values for semiconducting CuO hydrogen gas sensors. These results show that morphology plays an important role in the gas sensing performance of CuO and can be effectively applied in the further development of gas sensors based on p‐type semiconductors.     

On‐Demand Nanoscale Manipulations of Correlated Oxide Phases

Controlling material properties at the nanoscale is a critical enabler of high performance electronic and photonic devices. A prototypical material example is VO₂, where a structural phase transition in correlation with dramatic changes in resistivity, optical response, and thermal properties demonstrates particular technological importance. While the phase transition in VO₂ can be controlled at macroscopic scales, reliable and reversible nanoscale control of the material phases has remained elusive. Here, reconfigurable nanoscale manipulations of VO₂ from the pristine monoclinic semiconducting phase to either a stable monoclinic metallic phase, a metastable rutile metallic phase, or a layered insulating phase using an atomic force microscope is demonstrated at room temperature. The capability to directly write and erase arbitrary 2D patterns of different material phases with distinct optical and electrical properties builds a solid foundation for future reprogrammable multifunctional device engineering.     

金属氧化物气敏元件的研究进展

气敏传感器在现代工农业、信息技术、环境监测等领域都有重要应用。随着这几个领域的发展,人类对其综合性能要求越来越强,进而不断积极改良气敏传感器的性能。金属氧化物气敏元件是利用金属氧化物半导体的表面电阻遇到被测气体发生变化的原理制成的电子器件,其选择性和稳定性是研究气敏元件的两项重要指标。文章概述了金属氧化物元件气敏特性的研究进展,介绍了基体材料、掺杂材料、气敏材料的制备工艺、电极材料及结构等几个因素对元件气敏特性的主要影响,并对各种因素的作用机理进行了分析。最后展望了金属氧化物气敏元件的发展前景。     

Growth of Single‐Crystalline Wurtzite Aluminum Nitride Nanotips with a Self‐Selective Apex Angle

Single‐crystalline, hexagonal aluminum nitride nanotips are fabricated using a vapor‐transport and condensation process (VTCP) on silicon substrates with or without a catalyst layer. The resultant tips have very sharp nanoscale apexes (～1 nm), while their bases and lengths are up to hundreds of nanometers wide and several micrometers long, respectively. It has been demonstrated that the thickness of the gold‐catalyst layer plays a critical role in controlling the size of the tip; in addition, a catalyst‐free growth mode has been observed, which results in lesser control over the nanotip morphology. Nevertheless, a remarkably narrow distribution of the apex angle of the nanotips, regardless of whether or not a catalyst was used in the VTCP, has been obtained. Compared with the commonly observed ridge and pyramid structures, the nanotips produced by VTCP have higher angles (～81°) between the tilted (221) and the basal (001) planes that encase it. A mechanism for this self‐selective apex angle in aluminum nitride nanotip growth is proposed.     

Direct Patterning of Metal Chalcogenide Semiconductor Materials

Lithography is one of the most widely used methods for cutting‐edge research and industrial applications, mainly owing to its ability to draw patterns in the micro and even nanoscale. However, the fabrication of semiconductor micro/nanostructures via conventional electron or optical lithography technologies often requires a time‐consuming multistep process and the use of expensive facilities. Herein, a low‐cost, high‐resolution, facile, and versatile direct patterning method based on metal–organic molecular precursors is reported. The ink‐based metal–organic precursors are found to operate as negative resists, with the material exposed by different methods (electron‐beam/laser/heat/ultraviolet (UV)) to render them insoluble in the development process. This technical process can deliver metal chalcogenide semiconductors with arbitrary 2D/3D patterns with sub‐50 nm resolution. Electron beam lithography, two‐photon absorption lithography, thermal scanning probe lithography, and UV photolithography are demonstrated for the direct patterning process. Different metal chalcogenide semiconductor nanodevices, such as photoconductive selenium‐doped Sb₂S₃ nanoribbons, p‐type PbS single‐nanowire field‐effect transistors, and p‐n junction CdS/Cu₂S nanowire solar cells, are fabricated by this method. This direct patterning technique is a versatile and simple micro/nanolithography technology with considerable potential for “lab‐on‐a‐chip” preparation of semiconductor devices.     

超宽禁带AlN材料及其器件应用的现状和发展趋势

作为一种Ⅲ-Ⅴ族化合物半导体材料,AlN不仅具有超宽直接带隙(6.2 eV)、高热导率、高电阻率、高击穿场强、优异的压电性能和良好的光学性能,而且AlN晶体还与其他Ⅲ-N材料具有非常接近的晶格常数和热膨胀系数。这些特点决定了AlN在GaN外延、紫外光源、辐射探测器、微波毫米波器件、光电器件、电力电子器件以及声表面波器件等领域具有广阔的应用前景。介绍了AlN材料在功率器件、深紫外LED、激光器、传感器以及滤波器等领域的应用现状,并对AlN材料及其应用的未来发展趋势进行了分析和展望。     

Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems Based on SnIP

Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic‐scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer‐like atomic‐scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III‐V, or II‐VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C₃N₄ hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.     

Crystallization and Grain Growth Kinetics for Precipitation‐Based Ceramics: A Case Study on Amorphous Ceria Thin Films from Spray Pyrolysis

The introductory part reviews the impact of thin film fabrication, precipitation versus vacuum‐based methods, on the initial defect state of the material and microstructure evolution to amorphous, biphasic amorphous‐nanocrystalline, and fully nanocrystalline metal oxides. In this study, general rules for the kinetics of nucleation, crystallization, and grain growth of a pure single‐phase metal oxide thin film made by a precipitation‐based technique from a precursor with one single organic solvent are discussed. For this a complete case study on the isothermal and non‐isothermal microstructure evolution of dense amorphous ceria thin films fabricated by spray pyrolysis is conducted. A general model is established and comparison of these thin film microstructure evolution to kinetics of classical glass‐ceramics or metallic glasses is presented. Knowledge on thermal microstructure evolution of originally amorphous precipitation‐based metal oxide thin films allows for their introduction and distinctive microstructure engineering in devices‐based on microelectromechanical (MEMS) technology such as solar cells, capacitors, sensors, micro‐solid oxide fuel cells, or oxygen separation membranes on Si‐chips.