Semiconductor Nanowires Research Articles

Bottom-up nanoscale patterning and selective deposition on silicon nanowires

We demonstrate a bottom-up process for programming the deposition of coaxial thin films aligned to the underlying dopant profile of semiconductor nanowires. Our process synergistically combines three distinct methods—vapor–liquid–solid nanowire growth, selective coaxial lithography via etching of surfaces (SCALES), and area-selective atomic layer deposition (AS-ALD)—into a cohesive whole. Here, we study ZrO2 on Si nanowires as a model system. Si nanowires are first grown with an axially modulated n-Si/i-Si dopant profile. SCALES then yields coaxial poly(methyl methacrylate) (PMMA) masks on the n-Si regions. Subsequent AS-ALD of ZrO2 occurs on the exposed i-Si regions and not on those masked by PMMA. We show the spatial relationship between nanowire dopant profile, PMMA masks, and ZrO2 films, confirming the programmability of the process. The nanoscale resolution of our process coupled with the plethora of available AS-ALD chemistries promises a range of future opportunities to generate structurally complex nanoscale materials and electronic devices using entirely bottom-up methods.

Different III-V semiconductor nanowires with quantum dots on silicon: growth by molecular-beam epitaxy and properties

Recently, III-V semiconductor nanostructures of reduced dimension attract more and more interest of researchers for the new generation devices creation. Combinations of nanostructures with different dimensions are of special interest, among them, for example, quantum dots in the body of nanowires. Such quantum dotsʼ size and location control is strictly determined by the growth parameters. As a result of effective relaxation of mechanical stresses on the lateral faces of nanowires, the integration of hybrid nanostructures with silicon technology is possible. In this work, we have demonstrated the possibility of GaP nanowires with GaAs quantum dots and AlGaP nanowires with InGaP quantum dots growth on silicon by molecular-beam epitaxy. The physical properties of the selected nanowires have been investigated. Growth experiments were performed using Riber Compact 21 setup, which is equipped, in addition to the growth chamber, with a vacuum-aligned chamber for gold deposition (metallization chamber). The morphological properties of the obtained nanostructures were studied by scanning electron microscopy. The optical properties of the nanostructures were investigated by the photoluminescence method. The analyses of morphological properties showed that GaP nanowires with GaAs quantum dots were formed predominantly in the <111> direction, in contrast to AlGaP nanowires with InGaP quantum dots, which in some cases changed the growth direction. The reason for the change in the direction of growth of nanowires may be the participation of indium in the growth process. With a sufficient content of indium in the gold catalyst droplet, such mixed droplet can etch the facets at the top of the nanowires, thereby descending to the side of the nanowires and changing the direction of nanowires growth. The studies of the optical properties of the grown nanostructures showed that the photoluminescence signal from InGaP quantum dots in AlGaP nanowires is observed at a temperature of –263 °C with a peak maximum of around 550 nm. Thus, the synthesized nanostructures are promising for optoelectronic applications, in particular, for creating sources of single-photons.

Kinking in Semiconductor Nanowires: A Review

The growth direction of nanowires (NWs) can change during synthesis as a result of stochastic processes or modulation of certain growth conditions. This phenomenon is known as kinking. Although deviations from a uniform vertical growth are typically considered to be undesirable, kinking opens a route for additional tweaking of the characteristics and functionalities of NWs in a controllable manner, thus extending the range of potential applications. In the present Review, we give an insight into the kinking mechanisms and summarize the most crucial factors that can lead to kinking of NWs during synthesis. Additionally, the properties and applications of kinked NWs are discussed.

Enhanced terahertz emission from mushroom-shaped InAs nanowire network induced by linear and nonlinear optical effects

The development of powerful terahertz (THz) emitters is the cornerstone for future THz applications, such as communication, medical biology, non-destructive inspection, and scientific research. Here, we report the THz emission properties and mechanisms of mushroom-shaped InAs nanowire (NW) network using linearly polarized laser excitation. By investigating the dependence of THz signal to the incidence pump light properties (e.g. incident angle, direction, fluence, and polarization angle), we conclude that the THz wave emission from the InAs NW network is induced by the combination of linear and nonlinear optical effects. The former is a transient photocurrent accelerated by the photo-Dember field, while the latter is related to the resonant optical rectification effect. Moreover, the p-polarized THz wave emission component is governed by the linear optical effect with a proportion of ∼85% and the nonlinear optical effect of ∼15%. In comparison, the s-polarized THz wave emission component is mainly decided by the nonlinear optical effect. The THz emission is speculated to be enhanced by the localized surface plasmon resonance absorption of the In droplets on top of the NWs. This work verifies the nonlinear optical mechanism in the THz generation of semiconductor NWs and provides an enlightening reference for the structural design of powerful and flexible THz surface and interface emitters in transmission geometry.

Study of the transition from resonance to bound states in quantum dots embedded on a nanowire using the [formula omitted] method

We study the band structure of semiconductor nanowires with quantum dots embedded in them. The band structure is calculated using the Rayleigh–Ritz variational method. We consider quantum dots of two different types, one type is defined by electrostatic potentials applied to the nanowire, while the other one is defined by adding materials with band offsets with respect to the band parameters of the nanowire. We are particularly interested in the appearance of discrete energy levels in the gap between the conduction band and the valence band of the nanostructure, and in the dependence of the energy of these levels with the intensity of a magnetic field applied along the wire. It is shown that several scenarios are possible, being of particular interest the possibility of transforming states of the discrete into resonances and vice versa.

Self-Catalytic Growth of Elementary Semiconductor Nanowires with Controlled Morphology and Crystallographic Orientation.

While the orientation-dependent properties of semiconductor nanowires have been theoretically predicted, their study has long been overlooked in many fields owing to the limits to controlling the crystallographic growth direction of nanowires (NWs). We present here the orientation-controlled growth of single-crystalline germanium (Ge) NWs using a self-catalytic low-pressure chemical vapor deposition process. By adjusting the growth temperature, the orientation of growth direction in GeNWs was selectively controlled to the ⟨110⟩, ⟨112⟩, or ⟨111⟩ directions on the same substrate. The NWs with different growth directions exhibit distinct morphological features, allowing control of the NW morphology from uniform NWs to nanoribbon structures. Significantly, the VLS-based self-catalytic growth of the ⟨111⟩ oriented GeNW suggests that NW growth is possible for single elementary materials even without an appropriate external catalyst. Furthermore, these findings could provide opportunities to investigate the orientation-dependent properties of semiconductor NWs.

Thermoelectric Characteristics of InAs Nanowire Networks Directly Grown on Flexible Plastic Substrates

III-V semiconductor nanowires have shown promise for thermoelectric applications, but their use in practical devices has conventionally been hindered by complex fabrication processes and device integration. Here, we characterize the thermoelectric properties of InAs nanowire networks directly grown on flexible polyimide plastic. The n-type nanowire networks achieve a high room-temperature Seebeck coefficient of −110.8 μV K–1 and electrical conductivity of 41 S cm–1, resulting in a thermoelectric power factor of 50.4 μW m–1 K–2. Moreover, the nanowire networks show remarkable mechanical flexibility with a relative change in resistance below 0.01 at bending radii below 5.2 mm. We further establish the thermoelectric performance of InAs nanowire networks on plastic using a facile proof-of-concept thermoelectric generator producing a maximum power of 0.44 nW at a temperature gradient of 5 K. The findings indicate that direct growth of III-V nanowire networks on plastic substrates shows promise for the development of flexible thermoelectrics applications.

Bias-Switchable Photoconductance in a Nanoscale Ge Photodetector Operated in the Negative Differential Resistance Regime

Recent advances in nanoscale optoelectronic Ge devices have exposed their enormous potential for highly sensitive visible and near-infrared CMOS compatible photodetectors. In this respect, Ge nanowires, due to their nanocylinder resonator shape, have established themselves as a promising platform to significantly enhance the performance of photodetectors. Here, we present a highly sensitive polarity switchable Ge nanowire photodetector embedded in a monolithic and single-crystalline metal–semiconductor nanowire heterostructure. Operated in the negative differential resistance regime, effective dark current suppression up to a factor of 100 is achieved. In this configuration, a bias-switchable positive and negative photoconductance is observed and systematically analyzed. Further, a remarkably strong polarization anisotropy with a maximum TM/TE ratio of 33 was found for positive photoconductance. Most notably, presenting a Ge-based photodetector combining switchable photoconductance and effective dark current suppression may pave the way for advanced applications, including highly resolved imaging and light effect transistors.

Double Nanowires for Hybrid Quantum Devices

AbstractParallel 1D semiconductor channels connected by a superconducting strip constitute the core platform in several recent quantum device proposals that rely, for example, on Andreev processes or topological effects. In order to realize these proposals, the actual material systems must have high crystalline purity, and the coupling between the different elements should be controllable in terms of their interfaces and geometry. A strategy for synthesizing double InAs nanowires by the vapor‐liquid‐solid mechanism using III‐V molecular beam epitaxy is presented. A superconducting layer is deposited onto nanowires without breaking the vacuum, ensuring pristine interfaces between the superconductor and the two semiconductor nanowires. The method allows for a high yield of merged as well as separate parallel nanowires with full or half‐shell superconductor coatings. Their utility in complex quantum devices by electron transport measurements is demonstrated.

High electron mobility in strained GaAs nanowires

Transistor concepts based on semiconductor nanowires promise high performance, lower energy consumption and better integrability in various platforms in nanoscale dimensions. Concerning the intrinsic transport properties of electrons in nanowires, relatively high mobility values that approach those in bulk crystals have been obtained only in core/shell heterostructures, where electrons are spatially confined inside the core. Here, it is demonstrated that the strain in lattice-mismatched core/shell nanowires can affect the effective mass of electrons in a way that boosts their mobility to distinct levels. Specifically, electrons inside the hydrostatically tensile-strained gallium arsenide core of nanowires with a thick indium aluminium arsenide shell exhibit mobility values 30–50 % higher than in equivalent unstrained nanowires or bulk crystals, as measured at room temperature. With such an enhancement of electron mobility, strained gallium arsenide nanowires emerge as a unique means for the advancement of transistor technology.

Epitaxial type-I and type-II InAs-AlAsSb core–shell nanowires on silicon

Low-bandgap semiconductor nanowires (NWs) attract considerable interest for mid-infrared (MIR) photonics and optoelectronics, where ideal candidate materials require surface-passivated core–shell systems with large tunability in band offset, lineup, and emission wavelength while maintaining close lattice-matching conditions. Here, we propose and demonstrate epitaxial InAs–AlAsSb core–shell NW arrays on silicon (Si) that offer exceptional control over both the internal strain close to lattice-matching as well as band lineups tunable between type-I and type-II, with almost no analogue in the III–V materials family. We develop direct monolithic growth of high-uniformity InAs–AlAsSb NWs with wide tunability in shell composition and employ correlated Raman scattering and micro-photoluminescence spectroscopy to elaborate the interplay among hydrostatic strain, band lineup, and emission energy of the NW core luminescence tuned from ∼0.4 to 0.55 eV. Electronic structure calculations further support the experimentally observed tunability between type-I and type-II band lineups. The Si-integrated InAs-AlAsSb NW materials system holds large prospects not only for on-chip MIR photonics but also for other applications including high-speed transistors and NW-based hot carrier solar cells.

The application of one-dimensional nanostructures in terahertz frequency devices

One-dimensional nanostructures commonly refer to nanomaterials with a large length-to-diameter ratio, such as nanowires, nanotubes, nanorods, and nanopillars. The nanoscale lateral dimensions and high aspect ratios of these (quasi) one-dimensional nanostructures result in fascinating optical and electrical properties, including strongly anisotropic optical absorption, controlled directionality of light emission, confined charge-carrier transport and/or ballistic transport, which make one-dimensional nanostructures ideal building blocks for applications in highly integrated photonic, electronic, and optoelectronic systems. In this article, we review recent developments of very high (terahertz) frequency devices based on these one-dimensional nanostructures, particularly focusing on carbon nanotubes and semiconductor nanowires. We discuss state-of-the-art nanomaterials synthesis, device-fabrication techniques, device-operating mechanisms, and device performance. The combination of nanotechnology and terahertz science is a nascent research field which has created advanced THz sources, detectors, and modulators, leading to terahertz systems with extended functionalities. The goal of this article is to present the up-to-date worldwide status of this field and to highlight the current challenges and future opportunities.

High-detectivity tin disulfide nanowire photodetectors with manipulation of localized ferroelectric polarization field

Abstract Tin sulfide semiconductor nanowires (NWs) have been widely investigated for photodetection applications because of their good optical and electrical properties. Herein, we synthesized n-type SnS2 NWs and then fabricated SnS2 NW photodetectors with a ferroelectric polymer side-gate. The strong electric field induced by ferroelectric polymer can effectively suppress the dark current and improve the detectivity in SnS2 NW photodetectors. The photodetectors after polarization depletion exhibit a high photoconductive gain of 4.0 × 105 and a high responsivity of 2.1 × 105 A W−1. Compared with devices without polarization depletion, the detectivity of polarization-depleted photodetectors is improved by at least two orders of magnitude, and the highest detectivity is 1.3 × 1016 Jones. Further, the rise and fall time are 56 and 91 ms respectively, which are about tens of times faster than those without polarization depletion. The device also shows a good spectral response from ultraviolet to near-infrared. This study demonstrates that ferroelectric materials can enhance optoelectronic properties of low-dimensional semiconductors for high-performance photodetectors.

Adiabatic topological pumping in a semiconductor nanowire

The adiabatic topological pumping is proposed by periodically modulating a semiconductor nanowire double-quantum-dot chain. We demonstrate that the quantized charge transport can be achieved by a nontrivial modulation of the quantum-dot well and barrier potentials. When the quantum-dot well potential is replaced by a time-dependent staggered magnetic field, the topological spin pumping can be realized by periodically modulating the barrier potentials and magnetic field. We also demonstrate that in the presence of Rashba spin–orbit interaction, the double-quantum-dot chain can be used to implement the topological spin pumping. However, the pumped spin in this case can have a quantization axis other than the applied magnetic field direction. Moreover, we show that all the adiabatic topological pumping are manifested by the presence of gapless edge states traversing the bandgap as a function of time.

Atomic bonding-engineered heterogeneous integration of semiconductor nanowires by femtosecond laser irradiation for a miniaturized photodetector

Heterogeneous integration of semiconductor nanowires (NWs) incorporating the advantages of various materials is vital for developing new generation nanoscale devices. To date, the integration issues, especially the atomic bonding integration, remain a grand challenge due to the high melting point and lattice mismatches of heterogeneous materials. Herein, atomic bonding-engineered heterogeneous integration of semiconductor NWs is successfully achieved based on femtosecond (fs) laser irradiation. The nanobraze-welding mechanism is revealed for the formation of atomic-level bonding between CuO and ZnO NWs. A laser irradiation-induced diffusion region is observed at the CuO/ZnO hetero-interface, which remarkably broadens the carrier transport channels to optimize the electrical properties of the CuO/ZnO NWs p-n junction. Further simulation and band gap calculation reveal the absorption of laser energy via single-photon excitation in CuO NWs and two-photon excitation in ZnO NWs. A high-performance photodetector based on laser-nanobrazed CuO/ZnO NWs p-n junction is fabricated, which exhibits a high responsivity (9.86 A/W), fast rise and decay time (0.560 s and 2.056 s). This semiconductor NWs atomic-level bonding integration may inspire the widespread application of 1D nanomaterials and reveals a prospective pathway to develop miniaturized and multi-functional electronic devices by semiconductor NWs integration.

Catalyzed Growth for Atomic-Precision Colloidal Chalcogenide Nanowires and Heterostructures: Progress and Perspective.

One-dimensional colloidal semiconductor nanowires are of wide interest in nanoscale electronics and photonics. As compared to the zero-dimensional counterparts, their geometrical anisotropy offers an additional degree of freedom to tailor the electronic and optical properties and enables customized heterostructures with increased complexity. The colloidal synthetic chemistry developed over past decades has fueled the emergence of diverse one-dimensional nanocrystals and heterostructures, whereas the synthetic pursuit for compositionally and structurally defining them at the atomic-level precision remains yet a giant challenge. Catalyzed growth, wherein nanowires grow at the catalyst-nanowire interfaces in a layer-by-layer manner, offers a promising path toward such an ultimate goal. In this Perspective, we will take a close look at how catalyzed growth would enable the on-demand, atomic-precision control of colloidal nanowires and their heterostructures. We then further highlight their potentials for constructing higher-order heteroarchitectures with new and/or enhanced performances. Finally, we conclude with a forward-looking perspective on future challenges.

Semiconductor Nanowire‐Based Cellular and Subcellular Interfaces

AbstractThe highly intricate structures of biological systems make the precise probing of biological behaviors at the cellular‐level particularly difficult. As an advanced toolset capable of exploring diverse biointerfaces, high‐aspect‐ratio nanowires stand out with their unique mechanical, optical, and electrical properties. Specifically, semiconductor nanowires show much promise in their tunability and feasibility for synthesis and fabrication. Thus far, semiconductor nanowires have shown favorable results in deciphering biological communications and translating this cellular language through the nanowire‐based biointerfaces. In this perspective, the synthesis and fabrication methods for different kinds of nanowires and nanowire‐based structures are first surveyed. Next, several cellular‐level nanowire‐enabled applications in biophysical dynamics probing, physiological or biochemical sensing, and biological activity modulation are highlighted. Then, the progress of functionalized nanowires in drug delivery and bioenergy production is reviewed. Finally, the current limitations of nanowires and an outlook into the next generation of nanowire‐based devices at the biointerfaces are concluded.

Semiconductor Nanowire Arrays for High‐Performance Miniaturized Chemical Sensing

AbstractChemiresistive sensing is one of the most promising technologies for portable and miniaturized chemical sensing, with applications ranging from air quality monitoring to explosive detection and medical diagnostics. Recently, there have been growing efforts in developing microchip based chemical sensors operating at room temperature with high sensitivity, selectivity, spatial and temporal resolution, long‐term stability, and cost‐effectiveness. Here, the engineering of highly performing miniaturized gas sensors consisting of chemiresistive vertical indium phosphide nanowire (NW) arrays is reported for the first time, and their potential for the selective detection of nitrogen dioxide (NO2), a major air pollutant, is demonstrated. By carefully engineering the NW geometry (i.e., diameter and pitch), a superior sensing performance than those previously reported semiconductor‐based NO2 sensors is achieved, obtaining a limit of detection of 3.1 ppb at room temperature, with outstanding selectivity, and long‐term stability. Kinetic analysis and electrical simulation further reveal the array geometry correlated sensing mechanism, providing insights for the design of future NW array‐based devices. These findings indicate that, owing to their unique nanoscale structures, material properties, and CMOS compatible manufacture processes, III‐V compound semiconductor NW arrays present a new and promising chemical sensing platform for development of future high performance, miniaturized on‐chip sensing system.

(Invited) Enhanced Electron Phonon Scattering in Si Nanowires Covered By Oxide

In order to maintain gate controllability of electric current in nanoscale transistors, nanosheet or nanowire channels are required for future nodes. In Si covered by oxides, deformation potential greater than that in bulk has been used to reproduce electron mobility. Increase of the deformation potential results in decrease of phonon-limited mobility. However, physical origin of the increase of phonon scattering in nanostructures was not completely understood. Although atomistic calculations with H-terminated Si nanosheets partially explained the increase of phonon scattering, the amount of the increase of phonon scattering was not sufficient to reproduce experimental mobility or empirical values of deformation potential [1]. In this work, we calculated mobility in oxide covered semiconductor nanowires by Molecular dynamics (MD)-Landauer approach [2]. Based on MD simulations followed by transport calculations of tight-binding nonequilibrium Green’s function model, effects of the oxide layers on phonon scattering in the semiconductor nanowires was considered.The derived phonon-limited mobility of the free-standing Si nanowire (205 cm2V-1s-1) was almost the same as previously reported value in H-terminated Si nanowire [2], confirming the validity of our calculations. In the SiO2-covered Si nanowires, the mobility was decreased by half due to the SiO2 (95 cm2V-1s-1). Corresponding effective deformation potential was extracted by comparing the mobility calculated from MD-Landauer approach with the mobility calculated from Boltzmann transport equation. The corresponding deformation potential in SiO2-covered Si nanowires (D ac=22 eV) roughly agrees with the empirical deformation potentials in SOI films of the same thickness [3]. From the comparison between the free-standing and the SiO2-covered nanowires, we found the atomic displacements in the SiO2-covered Si nanowires were abnormally increased at the surface, which would result in the enhance of phonon scattering. Therefore, in order to precisely model the transport properties in future node’s transistors, atomistic descriptions of the interface between semiconductor and oxide were indispensable.[1] J. Li, JAP, 120, 174301, 2016.[2] T. Markussen, PRB, 95, 245210, 2017.[3] T. Ohashi, IEEE JEDS, 4, 278, 2016. Figure 1

Plasmon-induced spectral tunability of Perovskite nanowires

In this paper, plasmon-assisted spectral tunability in random media, composed of Perovskite (CsPbBr3) nanowires surrounded by Au nanoparticle clusters in polystyrene matrix, is achieved. The interaction between the surface plasmons and the quantum sources is observed to generate photoluminescence from the higher excited state energy levels of the excited semiconductor nanowires, which results in a blueshifted fluorescence emission of 50 nm. The localized surface plasmon properties are also determined to be tuned by plasmonic pumping of the quantum sources at different resonant frequencies. Thus, the first observation of the tunable blueshifted fluorescence emission of the semiconductor nanocrystals surrounded by plasmonic nanoparticle aggregates is achieved. The dramatic changes in the spectral profiles of the fluorescent nanowires are attributed to be due to the fast dynamics surface enhanced fluorescence mechanism.