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Contactless Optical Characterization of Carrier Dynamics in Free-Standing InAs-InAlAs Core-Shell Nanowires on Silicon
摘要： Contactless time-resolved pump-probe and external quantum efficiency measurements were performed on epitaxially grown free-standing wurtzite indium arsenide/indium aluminum arsenide (InAs-InAlAs) core-shell nanowires on Si (111) substrate from 77K to 293K. The first independent investigation of Shockley-Read-Hall, radiative and Auger recombination in InAs-based NWs is presented. Although the Shockley-Read Hall recombination coefficient was found to be at least two orders of magnitude larger than the average experimental values of other reported InAs materials, the Auger recombination coefficient was reported to be ten-fold smaller. The very low Auger and high radiative rates result in an estimated peak internal quantum efficiency of the core-shell nanowires as high as 22% at 77K, making these nanowires of potential interest for high efficiency mid-infrared emitters. A greater than two-fold enhancement in minority carrier lifetime was observed from capping nanowires with a thin InAlAs shell due to passivation of surface defects.
关键词： Auger recombination rate,radiative,Shockley-Read-Hall,Pump-probe spectroscopy,core-shell nanowires,surface/interface recombination velocity,minority carrier lifetime
更新于2025-09-23 15:23:52
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3D core-multishell piezoelectric nanogenerators
摘要： The thin film configuration presents obvious practical advantages over the 1D implementation in energy harvesting systems such as easily manufacturing and processing, and long-lasting and stable devices. However, ZnO-based piezoelectric nanogenerators (PENGs) generally rely on the exploitation of single-crystalline nanowires because of their self-orientation in the c-axis direction and ability to accommodate long deformations resulting in high piezoelectric performance. Herein, we show an innovative approach to produce PENGs by combining polycrystalline ZnO layers fabricated at room temperature by plasma-assisted deposition with supported small-molecule organic nanowires (ONWs) acting as 1D scaffolds. Such hybrid nanostructures present convoluted core-shell morphology, formed by a single-crystalline organic nanowire conformally surrounded by a poly-crystalline ZnO shell and combine the organic core mechanical properties with the ZnO layer piezoelectric response. In a step forward towards the integration of multiple functions within a single wire, we have also developed ONW-Au-ZnO nanoarchitectures including a gold shell acting as inner electrode achieving output piezo-voltages up to 170 mV. The synergistic combination of functionalities in the ONW-Au-ZnO devices promotes an enhanced performance generating piezo-currents one order of magnitude larger than the ONW-ZnO nanowires and superior to the thin film nanogenerators for equivalent and higher thicknesses.
关键词： piezoelectric nanogenerators,organic nanowires,ZnO,small-molecules,plasma deposition,core-shell nanowires
更新于2025-09-23 15:22:29
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Transparent Conductive Materials (Materials, Synthesis, Characterization, Applications) || Metal Nanowires
摘要： Metal nanowires are one-dimensional entities of metals of either single crystalline or polycrystalline nature [1]. Metal nanowires have attracted tremendous research attention since the last two decades, because of their important applications in plasmonics [2], electronics [3], electrocatalysis [4], and so on. In the past decade, researchers have attempted to coat metal nanowires on a transparent substrate as a transparent conductive ?lm (TCF) [5–7]. The visible light transparency and the conductivity of TCFs on the basis of metal nanowires have improved rapidly, being comparable with the performance of the state-of-the-art indium tin oxide (ITO) TCFs [8–10]. The recognition of the potential applications of metal nanowire TCFs stimulates research zeal for the synthesis of metal nanowires. So far, a range of metal nanowires have been synthesized, including Ag nanowires (AgNWs) [11], Au nanowires (AuNWs) [12], Cu nanowires (CuNWs) [13], and Pt nanowires [14]. Bicomponent metal nanowires, such as Cu@Ni [15], Ag@Au [16], Cu@Ag [17], Ag@Ni [18], and Cu@Pt [19] core@shell nanowires, have also been synthesized. These nanowires have been coated on a substrate to produce TCFs, and the performance has been characterized. At early stage of the research on metal nanowire TCFs, the transparency was lower than 80%, and the sheet resistance was as large as several kΩ to MΩ. Both experimental investigation and theoretical modeling have been extensively carried out to improve the performance of metal nanowire TCFs.
关键词： Core@shell nanowires,Transparent conductive films,Plasmonics,Electronics,Au nanowires,Metal nanowires,Ag nanowires,Cu nanowires,Electrocatalysis
更新于2025-09-23 15:21:21
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<i>(Invited)</i> Large-Scale DFT Study of Ge/Si 3D Nanoislands and Core-Shell Nanowires
摘要： Density functional theory (DFT) calculations have been playing important roles to clarify the structures of semiconductor surfaces at atomic scale. However, DFT studies of complex nanostructures are usually impossible because conventional DFT methods cannot treat large systems containing many thousands of atoms. In this paper, we survey our large scale DFT study on (i) the growth of Ge 3D nanostructure on Si(001) substrate and (ii) the atomic and electronic structures of Si/Ge or Ge/Si core-shell nanowires, using our linear-scaling DFT code CONQUEST. The code uses large-scale DFT techniques and has high efficiency on massively parallel computers. We demonstrate that CONQUEST can calculate the atomic positions of the realistic models of nanostructures observed in experiments and can clarify the unique electronic properties of these nano-structured materials.
关键词： nanoislands,CONQUEST,Ge/Si,DFT,core-shell nanowires
更新于2025-09-23 15:21:21
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Excitonic Aharonov-Bohm Oscillations in Core-Shell Nanowires
摘要： Phase coherence in nanostructures is at the heart of a wide range of quantum effects such as Josephson oscillations between exciton–polariton condensates in microcavities, conductance quantization in 1D ballistic transport, or the optical (excitonic) Aharonov–Bohm effect in semiconductor quantum rings. These effects only occur in structures of the highest perfection. The 2D semiconductor heterostructures required for the observation of Aharonov–Bohm oscillations have proved to be particularly demanding, since interface roughness or alloy fluctuations cause a loss of the spatial phase coherence of excitons, and ultimately induce exciton localization. Experimental work in this field has so far relied on either self-assembled ring structures with very limited control of shape and dimension or on lithographically defined nanorings that suffer from the detrimental effects of free surfaces. Here, it is demonstrated that nanowires are an ideal platform for studies of the Aharonov–Bohm effect of neutral and charged excitons, as they facilitate the controlled fabrication of nearly ideal quantum rings by combining all-binary radial heterostructures with axial crystal-phase quantum structures. Thanks to the atomically flat interfaces and the absence of alloy disorder, excitonic phase coherence is preserved even in rings with circumferences as large as 200 nm.
关键词： excitonic Aharonov–Bohm effect,phase coherence,core–shell nanowires,3D nanostructures
更新于2025-09-23 15:21:01
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Zirconium Nitride for Plasmonic Cloaking of Visible Nanowire Photodetectors
摘要： Light scattered by a photodetector disturbs the probing field, resulting in noise. Cloaking is an effective method to reduce this noise. Here we investigate theoretically an emerging plasmonic material, zirconium nitride (ZrN), as a plasmonic cloak for silicon (Si) nanowire-based photodetectors and compare it with a traditional plasmonic material, gold (Au). Using Mie formalism, we have obtained the scattering cancelation across the visible spectrum. We found that ZrN cloaks produce a significant decrease in the scattering from bare Si nanowires, which is 40% greater than that obtained with Au cloaks in the wavelength region of 400–500 nm. The scattering cancelations become comparable at 550 nm, with Au providing a better scattering cancelation compared to ZrN over the wavelength region of 600–700 nm. To include the absorption and provide a measure of overall performance on noise reduction, a figure of merit (FOM), defined as the ratio of the absorption efficiency and the scattering efficiency of the cloaked nanowire to that of the bare Si nanowire, was calculated. We show that the optimized ZrN cloak provides up to 3 times enhancement of the FOM over a bare Si NW and a 60% improvement over an optimized Au-cloaked NW, in the wavelength region of 400–500 nm. An optimized Au-cloaked NW shows up to 17.69 times improvement in the wavelength region of 600–700 nm over a bare Si NW and up to a 2.7 times improvement over an optimized ZrN-cloaked NW. We also predicted the optimal dimensions for the cloaked NWs with respect to the largest FOM at various wavelengths between 400 and 650 nm.
关键词： Plasmonic cloaking,Core-shell,Nanowires,Emerging plasmonic materials,Zirconium nitride,Scattering cancelation
更新于2025-09-19 17:13:59
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Vis–IR wide-spectrum photodetector at room temperature based on p-n junction-type GaAs1-xSbx/InAs core-shell nanowire
摘要： Infrared (IR) detection at room temperature is very important in many fields. Nanoscale wide-spectrum photodetectors covering IR range are still rare, although they are desired in many applications, such as in integrated optoelectronic devices. Here, we report a new kind of photodetector based on p?n heterojunction-type GaAs1-xSbx/InAs core-shell nanowires. The photodetectors demonstrate high response to the lights ranging from visible light (488 nm) to short-wavelength IR (1800 nm) at room temperature under a very low bias voltage of 0.3 V. The high performances of the devices include an ultralow dark current (32 pA at room temperature), a fast response speed (0.45 ms) to 633 nm light, high responsivity to 1310 nm telecommunication light (0.12 A/W), and high response even to 1800 nm light (on/off ratio of 2.5), etc. Besides, the devices also show excellent rectifying I-V characteristics (the current rectification ratio being ~178 in a voltage range of ± 0.3 V). These results suggest that the GaAs1-xSbx/InAs core-shell nanowires devices are promising for applications in nanoelectronic devices, optoelectronic devices and integrated optoelectronic devices.
关键词： P-N junction,IR,III-V nanowires,core-shell nanowires,Photodetector
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Plasmonic nonlinearity in GaAs/In <sub/>0.20</sub> Ga <sub/>0.80</sub> As core/shell nanowires
摘要： We have investigated the plasmonic response of GaAs/In0.20Ga0.80As core/shell nanowires driven resonantly by strong THz fields with the amplitude of few MV/cm. The plasmon mode exhibits a systematic redshift with the suppression of the spectral weight with the increase of the driving THz field. Interestingly, the scaling of the plasmon parameters does not follow the usual quadratic behavior, indicating inhomogeneous intervalley electron scattering across the nanowire.
关键词： THz fields,intervalley electron scattering,GaAs/In0.20Ga0.80As,Plasmonic nonlinearity,core/shell nanowires
更新于2025-09-16 10:30:52