InAs/GaAs和InAs/InxGa1-xAs/GaAs纳米线异质结构的生长研究

利用金辅助金属有机化学气相沉淀法(MOCVD)在GaAs(111)B衬底上分别制备了InAs/GaAs和InAs/In _{x Ga1-xAs/GaAs(0≤x≤1)纳米线异质结构.实验结果显示,直接生长在GaAs纳米线上的InAs纳米线生长方向杂乱或者沿着GaAs纳米线侧壁向衬底方向生长,生长的含有In x Ga1-xAs组分渐变缓冲段的InAs/In x Ga1-x关键词： 纳米线异质结构 xGa1-xAs')" href="#">InxGa1-xAs 组分渐变缓冲层 金属有机化学气相沉淀法}     

Raman mapping of laser-induced changes and ablation of InAs nanowires

Indium arsenic (InAs) nanowires were irradiated with a focused laser beam, followed by in situ Raman spectroscopy mapping and scanning electron microscopy imaging to investigate the changes of the nanowires due to laser irradiation. It was found that laser irradiation with the power intensity above a certain threshold causes arsenic (As) atoms to disintegrate from InAs and accumulate on the surface of the nanowire; the accumulated As atoms evaporate under the continued laser irradiation. This process reduces the As content in the nanowire. The reduction of As content, in turn, lowers the melting temperature of the nanowire locally and facilitates laser ablation, which eventually fractures the nanowire. The laser irradiation induced changes of the InAs nanowires are attributed to the local temperature rises due to the irradiation, as confirmed by the Raman peak shifts. The results from this work show that in situ Raman spectroscopy mapping can provide detailed information about the entire process of laser-induced change and ablation of InAs nanowires and has the potential to become a powerful tool for the characterization of laser modification of nanowires and other nanometer-sized objects.     

基于微芯片的透射电子显微镜的低温纳米精度电子束刻蚀与原位电学输运性质测量

利用微芯片制备技术制备了带有电极的原位电学薄膜芯片,并结合自制的原位透射电镜样品台,实现了低温下透射电子显微镜聚焦电子束对InAs纳米线的精细刻蚀以及不同温度下的原位电学性能测量.研究发现,随着刻蚀区域截面积的减小,纳米线的电导率也随之减小.当纳米线的截面积从大于10000 nm2刻蚀至约800 nm2时,纳米线电导的减小速率与截面积的减小具有线性关系.同时利用低温聚焦电子束刻蚀,在InAs纳米线上原位制备了一个10 nm的纳米点,并在77与300 K下对该纳米点进行了电学性能测量.通过测量发现在77 K时出现库仑阻塞效应,发生了电子隧穿现象;而300 K时,热扰动提供的能量使这种现象消失.     

(InAs)1/(GaSb)1超晶格纳米线第一原理研究

半导体纳米线作为纳米器件的作用区和连接部分具有理想的形状, 把电子运动和原子周期性限制在一维结构当中.通过体材料的已知特性, 有效地选择材料组分使纳米线的低维结构优点更加突出.此外, 还可以通过其他方式来调整纳米线特性, 如控制纳米线直径、晶体学生长方向、结构相、表面晶体学晶面和饱和 度等内部或固有的特性;施加电场、磁场、热场和力场等外部影响. 体材料InAs和GaSb的晶格常数非常相近, 因此InAs/GaSb异质结构晶格失配很小, 可生长成为优良的红外光电子材料.另外, 体材料InAs在二元III---V化合物半导体中具有最低的有效质量, 这使得电子限制在InAs层的InAs/GaSb超晶格具有良好的输运特性. 本文通过第一原理计算研究轴线沿[001]和[111]闪锌矿晶体学方向的 (InAs)₁/(GaSb)₁超晶格纳米线(下标表示分子或双原子单层的数量) 的结构、电子和力学特性, 以及它们随纳米线直径(线径约为0.5---2.0 nm)的变化规律.另外, 分析了外部施加的应力对电子特性的影响, 考察了不同线径(InAs)₁/(GaSb)₁超晶格纳米线的电子带边能级随轴向应变的变化, 从而确定超晶格电子能带的带边变形势.     

Composition analysis of single semiconductor nanowires using pulsed-laser atom probe tomography

We report the composition analysis of single InAs and Si semiconductor nanowires using pulsed-laser atom probe tomography. The experimental conditions and sample geometries needed to realize 3-D composition mapping are described in detail. InAs mass spectra obtained using voltage pulses and laser pulses are compared, and are found to be superior for pulsed-laser evaporation. The ability to analyze intrinsic Si nanowires using pulsed laser evaporation is demonstrated. No peaks associated with the gold catalyst used were found in the InAs or the Si nanowire mass spectra. PACS 68.70.+w; 61.82.Fk; 61.72.Ss     

Electronic properties of InAs/GaAs nanowire superlattices

The electronic properties of strained InAs/GaAs nanowire superlattices are computed using a semi-empirical sp³d⁵s^* tight-binding model, taking strains, piezoelectric fields and image charge effects into account. Strain relaxation appears to be efficient in nanowire heterostructures, but is highly inhomogeneous in thin InAs layers. It digs a well in the conduction band that traps the electrons at the surface of the nanowires. This likely decreases the oscillator strength and might ease the capture of the electrons by nearby surface defects.     

Phonon thermal transport in InAs nanowires with different size and growth directions

We investigate the phonon thermal transport properties in InAs nanowires with different size and growth directions by using nonequilibrium molecular dynamics methods. The results show a remarkable anisotropy for the thermal conductivity in InAs nanowire. It is found that the thermal conductivity along [110] growth direction is about three times larger than that along [100] or [111] direction. With the increase of temperature, the thermal conductivity along [110] direction decreases significantly. However, the thermal conductivity along other two directions is not sensitive to temperature. Moreover, we find a crossover from ballistic to ballistic-diffusive thermal transport for a certain length of InAs nanowire. A brief physical analysis of these results is given. It is suggested that the anisotropy of thermal conductivity is common for nanowires with zinc blende structures.     

悬空氧化铟纳米线晶体管制备与光电性能表征

一维(1D)半导体纳米线在纳米电子学和纳米光子学中表现出色。然而,纳米线晶体管的电特性对纳米线与衬底之间的相互作用非常敏感,而优化器件结构可以改善纳米线晶体管的电学和光电检测性能。本文报道了通过一步式光刻技术制造的悬浮式In₂O₃纳米线晶体管,显示出54.6 cm²V^?1s^?1的高迁移率和241.5 mVdec^?1的低亚阈值摆幅。作为紫外光电探测器,光电晶体管显示出极低的暗电流(~10?13 A)和高响应度1.6×10⁵ A?W^?1。悬浮晶体管的沟道材料的这种简单而有效的制备方法可广泛用于制造高性能微纳米器件。     

Germanium nanowires: from synthesis, surface chemistry, and assembly to devices

A low temperature synthesis of single crystalline Ge nanowires via chemical vapor deposition is enabled by balancing the feedstock and its diffusion in growth seeds. Understanding and optimizing the synthetic chemistry leads to deterministic nanowire growth at well-defined locations and bulk quantity production of homogeneous nanowires, both of which greatly facilitate the assembly toward parallel nanowire arrays. Surface chemistry studies reveal that p- and n-type Ge nanowires undergo different oxidation routes and the surface oxide induced states cause opposite band bending for nanowires with different doping. Furthermore, long chain alkanethiols form a dense and uniform protection layer on Ge nanowire surfaces and therefore afford excellent oxidation resistance. Finally, high performance field effect transistors are constructed on Ge nanowires with both thermally grown SiO₂ and atomic layer deposited HfO₂ as gate dielectrics. PACS 73.63.-b; 73.63.B6; 73.22.-f; 73.20.At; 73.90.+f     

Improved gate-control in InAs nanowire structures by the use of GdScO3 as a gate dielectric

We investigated the properties of gadolinium scandate (GdScO₃) as a gate dielectric for top-gate electrodes on undoped InAs nanowires. It is demonstrated that due to the high dielectric constant of GdScO₃ (k=22), a better control of the conductance of the nanowire is achieved compared to a reference SiO₂-isolated back-gate electrode. We analyzed the output and transfer characteristics of top-gate-controlled InAs wires at room temperature and at temperatures down to 4 K. Owing to the good coverage of the InAs nanowire by the 50-nm-thick GdScO₃ layer, which was deposited by pulsed-laser deposition, the gate leakage current is sufficiently suppressed.     

Study of the in-plane and c-axis fluctuation conductivity of melt-textured YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> under hydrostatic pressure

Strongly confined nano-systems, such as one-dimensional nanowires, feature deviations in their structural, electronic and optical properties from the corresponding bulk. In this work, we investigate the behavior of long-wavelength, optical phonons in vertical arrays of InAs nanowires by Raman spectroscopy. We attribute the main changes in the spectral features to thermal anharmonicity, due to temperature effects, and rule out the contribution of quantum confinement and Fano resonances. We also observe the appearance of surface optical modes, whose details allow for a quantitative, independent estimation of the nanowire diameter. The results shed light onto the mechanisms of lineshape change in low-dimensional InAs nanostructures, and are useful to help tailoring their electronic and vibrational properties for novel functionalities.     

Effects of surface roughness on the electrical characteristics of ZnO nanowire field effect transistors

We have systematically investigated the effects of surface roughness on the electrical characteristics of ZnO nanowire field effect transistors (FETs) before and after passivation by poly (methyl metahacrylate) (PMMA), a polymer-insulating layer. To control the surface morphology of ZnO nanowires, ZnO nanowires were grown by the vapor transport method on two different substrates, namely, an Au-catalyzed sapphire and an Au-catalyzed ZnO film/sapphire. ZnO nanowires grown on the Au-catalyzed sapphire substrate had smooth surfaces, whereas those grown on the Au-catalyzed ZnO film had rough surfaces. Electrical characteristics such as the threshold voltage shift and transconductance before and after passivation were strongly affected by the surface morphology of ZnO nanowires.     

Band-offset effect on localization of carriers and p-type doping of InAs/GaAs core–shell nanowires

The electronic properties and p-type doping mechanism of InAs/GaAs core–shell nanowires are studied by using the first-principles calculations within density-functional theory. The core–shell structure of nanowires creates one-dimensional band offset at the InAs/GaAs interface. The magnitude of band offset depends on the sizes of core and shell. We find that a highly efficient p-type doping in InAs/GaAs core–shell nanowires can be achieved by introducing the Cd-impurity into the GaAs shell, utilizing the band-offset effect. It is because the valence-band electrons can spontaneously transfer to the Cd-impurity level, resulting in one-dimensional hole gas in the InAs core of nanowires.     

Coulomb blockade and hopping transport behaviors of donor-induced quantum dots in junctionless transistors

The ionized dopants, working as quantum dots in silicon nanowires, exhibit potential advantages for the development of atomic-scale transistors. We investigate single electron tunneling through a phosphorus dopant induced quantum dots array in heavily n-doped junctionless nanowire transistors. Several subpeaks splittings in current oscillations are clearly observed due to the coupling of the quantum dots at the temperature of 6 K. The transport behaviors change from resonance tunneling to hoping conduction with increased temperature. The charging energy of the phosphorus donors is approximately 12.8 meV. This work helps clear the basic mechanism of electron transport through donor-induced quantum dots and electron transport properties in the heavily doped nanowire through dopant engineering.     

单根砷掺杂氧化锌纳米线场效应晶体管的电学及光学特性

采用化学气相沉积（CVD）的方法在砷化镓基底上合成直径为20 nm左右、长约数十微米的氧化锌纳米线,然后采用热扩散的方法,将生长于砷化镓基底之上的氧化锌纳米线通过600 ℃,30 min的有氧退火处理后,获得了砷掺杂的氧化锌纳米线.将获得的掺杂后的氧化锌纳米线采用电子束曝光以及真空溅射镀膜的方法将钛/金合金作为接触电极引出,从而构建成场效应晶体管.文中研究了单根氧化锌纳米线砷掺杂前后的电学特性,证实了通过砷掺杂来获得p型的氧化锌纳米线的可行性.构建的p型砷掺杂氧化锌场效应晶体管的跨导为35 nA/V,载流 关键词： p型ZnO纳米线 砷掺杂 场效应晶体管 光致发光     

Magnetism in atomic-size palladium contacts and nanowires

We have investigated Pd nanowires theoretically, and found that, unlike either metallic or free atomic Pd, they exhibit Hund's rule magnetism. In long, monostrand nanowires, we find a spin moment of 0.7 mu(B) per atom, whereas for short, monostrand nanowires between bulk leads, the predicted moment is about 0.3 mu(B) per nanowire atom. In contrast, a coaxial (6,1) nanowire was found to be nonmagnetic. The origin of the nanowire magnetism is analyzed.     

Patterned horizontal growth of ZnO nanowires on SiO2 surface

We report patterned horizontal growth of ZnO nanowires on SiO₂ surface for the study of electrical and luminescent characteristics of individual nanowires and for device applications. Patterns of gold catalytic seed islands with barrier layers which suppress vertical growth were employed to facilitate horizontal growth on SiO₂ surface. After the growth, ZnO nanowire devices are fabricated by patterning electrodes aligned over the seed islands and their device characteristics are investigated. We could also investigate history of synthesis conditions by obtaining local luminescence characteristics along individual nanowires.     

Structural and electrical properties of core–shell structured GaP nanowires with outer Ga2O3 oxide layers

This paper presents a review of our current experimental research on GaP nanowires grown by a vapor deposition method. Their structural, electrical, opto-electric transport, and gas-adsorption properties are reviewed. Our structural studies showed that a GaP nanowire consisted of a core–shell structure with a single-crystalline GaP core and an outer Ga₂O₃ layer. The individual GaP nanowires exhibited n-type field effects. Their electron mobilities were in the range of about 6 to 22 cm²/V s at room temperature. When the nanowires were illuminated with an ultraviolet light source, an abrupt increase of conductance occurred resulting from carrier generation in the nanowire and de-adsorption of adsorbed OH^- or O₂ ^- ions on the Ga₂O₃ surface shell. Using an intrinsic Ga₂O₃ shell layer as a gate dielectric, top-gated GaP nanowire field-effect transistors were fabricated and characterized. Like other metal oxide nanowires, the carrier concentration and mobility of GaP nanowires were significantly affected by the surface molecular adsorption of OH or O₂. The GaP nanowire devices were fabricated as sensors for NO₂, NH₃, and H₂ gases by using a simple metal decoration technique. PACS 73.63.-b; 72.80.Ey; 85.35.-p     

金属纳米线弹性性能的尺寸效应及其内在机理的模拟研究

本文应用分子动力学(MD)方法和改进分析型嵌入原子模型(MAEAM)研究了Ni, Al和V纳米线的弹性性能尺寸效应及表面对其影响, 并计算了相应完整晶格材料的弹性性能. 结果表明本文计算完整晶格材料的弹性性能与已有实验和理论的结果相符合. 而计算所得各金属纳米线的体模量明显低于相应块体材料的结果, 且随纳米线的尺寸增加而呈指数增加, 并接近于常数. 在此基础上, 通过研究Ni, Al和V纳米线表面能的尺寸效应及其分布特征进一步探讨了自由表面在尺寸影响纳米线弹性性能过程中的作用及其内在机理.     

The research on suspended ZnO nanowire field-effect transistor

This paper reports that a novel type of suspended ZnO nanowire field-effect transistors (FETs) were successfully fabricated using a photolithography process, and their electrical properties were characterized by I--V measurements. Single-crystalline ZnO nanowires were synthesized by a hydrothermal method, they were used as a suspended ZnO nanowire channel of back-gate field-effect transistors (FET). The fabricated suspended nanowire FETs showed a p-channel depletion mode, exhibited high on--off current ratio of ～10⁵. When V_DS=2.5 V, the peak transconductances of the suspended FETs were 0.396 μS, the oxide capacitance was found to be 1.547 fF, the pinch-off voltage V_TH was about 0.6 V, the electron mobility was on average 50.17 cm²/Vs. The resistivity of the ZnO nanowire channel was estimated to be 0.96× 10²Ω cm at V_GS = 0 V. These characteristics revealed that the suspended nanowire FET fabricated by the photolithography process had excellent performance. Better contacts between the ZnO nanowire and metal electrodes could be improved through annealing and metal deposition using a focused ion beam.