281 research outputs found
Ultrafast and reversible electrochemical lithiation of InAs nanowires observed by in-situ transmission electron microscopy
No full textThe electrochemical lithiation/delithiation processes of InAs nanowires (NWs) are studied by in-situ transmission electron microscopy. Our results indicate that InAs NWs have a fast lithiation speed of 275 nm/s and a high lithium ion (Li-ion) diffusion coefficient of 2.49 x 10(-8) cm(2)/s at room temperature. Upon lithiation, the Li-ion insertion firstly results in severe lattice distortions of InAs NWs, and the formation of Li3As and LixIn through the conversion and alloying processes take place on further lithiation. A small volume expansion of 157% is observed in full lithiation and is attributed to the naturally formed surface oxide layer. During the delithiation process, volume contraction and the dealloying of LixIn take place. Induced by the alloying and dealloying of LixIn, the dark and bright strips along the basal plane of InAs NWs appear and disappear alternately during the lithiation-delithiation cycling. Our results provide important insights into the lithiation/delithiation mechanism of III-V group nanomaterials and are envisaged to be helpful for designing lithium ion battery anode materials with fast lithiation speed, small volume expansion and reversible lithiation/delithiation processes. (C) 2015 Elsevier Ltd. All rights reserved.MOST of the China [2012CB932702, 2012CB932701]; NSF of China [11374022, 61371001, 11304003, 61321001]; Foundation for the Author of National Excellent Doctoral Dissertation of China [201241]; Specialized Research Fund for the Doctoral Program of Higher Education of China [20130001110030]SCI(E)[email protected]; [email protected]; [email protected]
Crystal phase- and orientation-dependent electrical transport properties of InAs nanowires
No full textWe
report a systematic study on the correlation of the electrical
transport properties with the crystal phase and orientation of single-crystal
InAs nanowires (NWs) grown by molecular-beam epitaxy. A new method
is developed to allow the same InAs NW to be used for both the electrical
measurements and transmission electron microscopy characterization.
We find both the crystal phase, wurtzite (WZ) or zinc-blende (ZB),
and the orientation of the InAs NWs remarkably affect the electronic
properties of the field-effect transistors based on these NWs, such
as the threshold voltage (VT), ON–OFF
ratio, subthreshold swing (SS) and effective barrier
height at the off-state (ΦOFF). The SS increases while VT, ON–OFF ratio,
and ΦOFF decrease one by one in the sequence of WZ
⟨0001⟩, ZB ⟨131⟩, ZB ⟨332⟩,
ZB ⟨121⟩, and ZB ⟨011⟩. The WZ InAs NWs
have obvious smaller field-effect mobility, conductivities, and electron
concentration at VBG = 0 V than the ZB
InAs NWs, while these parameters are not sensitive to the orientation
of the ZB InAs NWs. We also find the diameter ranging from 12 to 33
nm shows much less effect than the crystal phase and orientation on
the electrical transport properties of the InAs NWs. The good ohmic
contact between InAs NWs and metal remains regardless of the variation
of the crystal phase and orientation through temperature-dependent
measurements. Our work deepens the understanding of the structure-dependent
electrical transport properties of InAs NWs and provides a potential
way to tailor the device properties by controlling the crystal phase
and orientation of the NWs
Negative photoconductivity of InAs nanowire
No full textNegative photoconductivity is observed in InAs nanowires (NWs) without a surface defective layer. The negative photoconductivity is strongly dependent on the wavelength and intensity of the light, and is also sensitive to the environmental atmosphere. Two kinds of mechanisms are discerned to work together. One is related to gas adsorption, which is photodesorption of water molecules and photo-assisted chemisorption of O-2 molecules. The other one can be attributed to the photogating effect introduced by the native oxide layer outside the NWs.MOST [2012CB932702, 2012CB932701]; NSF of China [11374022, 61321001, 11528407]SCI(E)[email protected]
Schottky barrier heights at the interfaces between pure-phase InAs nanowires and metal contacts
No full textUnderstanding of the Schottky barriers formed at metal contact-InAs nanowire interfaces is of great importance for the development of high-performance InAs nanowire nanoelectronic and quantum devices. Here, we report a systematical study of InAs nanowire field-effect transistors (FETs) and the Schottky barrier heights formed at the contact-nanowire interfaces. The InAs nanowires employed are grown by molecular beam epitaxy and are high material quality single crystals, and the devices are made by directly contacting the nanowires with a series of metals of different work functions. The fabricated InAs nanowire FET devices are characterized by electrical measurements at different temperatures and the Schottky barrier heights are extracted from the measured temperature and gate-voltage dependences of the channel current. We show that although the work functions of the contact metals are widely spread, the Schottky barrier heights are determined to be distributed over 35-55 meV, showing a weak but not negligible dependence on the metals. The deduced Fermi level in the InAs nanowire channels is found to be in the band gap and very close to the conduction band. The physical origin of the results is discussed in terms of Fermi level pinning by the surface states of the InAs nanowires and a shift in pinned Fermi level induced by the metal-related interface states. (C) 2016 AIP Publishing LLC.National Basic Research Program of China [2012CB932700, 2012CB932703]; National Natural Science Foundation of China [91221202, 91421303, 11274021, 61321001]; Specialized Research Fund for the Doctoral Program of Higher Education of China [20120001120127]; Swedish Research Council (VR)SCI(E)[email protected]; [email protected]
Spin injection through an Fe/InAs interface
No full textThe spin dependence of the interface resistance between ferromagnetic Fe and InAs is calculated from first principles for specular and disordered (001) interfaces. Because of the symmetry mismatch in the minority-spin channel, the specular interface acts as an efficient spin filter with a transmitted current polarization between 98% and 89%. The resistance of a specular interface in the diffusive regime is comparable to the resistance of a few microns of bulk InAs. Symmetry breaking arising from interface disorder reduces the spin asymmetry substantially, and we conclude that efficient spin injection from Fe into InAs can only be realized using high-quality epitaxial interfaces
Quantitative analysis of strain distribution in InAs/InAs1−xSbx superlattices
No full textabstract: Atomic resolution transmission electron microscopy is performed to examine the strain distribution in an InAs/InAs1-xSbx superlattice grown on a (100)-GaSb substrate. The strain profiles reveal that the thickness of tensile regions in the superlattice is significantly lower than expected, with a corresponding increase in thickness of the compressive regions. Furthermore, significant grading is observed within the tensile regions of the strain profile, indicating Sb intermixing from the InAsSb growth surface. The results signify an effective reduction in the InAs layer thickness due to the anion (As-Sb) exchange process at the InAs-on-InAsSb interface. (C) 2013 AIP Publishing LLC.Copyright 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. along with the following message: The following article appeared in Applied Physics Letters, 103(6), 061908. doi:10.1063/1.4817969 and may be found at (http://scitation.aip.org/content/aip/journal/apl/103/6/10.1063/1.4817969)
Surface passivated InAs/InP core/shell nanowires
No full textWe report the growth and characterization of InAs nanowires capped with a 0.5–1 nm epitaxial InP shell. The low-temperature field-effect mobility is increased by a factor 2–5 compared to bare InAs nanowires. We extract the highest low-temperature peak electron mobilities obtained for nanowires to this date, exceeding 20 000 cm2 V s?1. The electron density in the nanowires, determined at zero gate voltage, is reduced by an order of magnitude compared to uncapped InAs nanowires. For smaller diameter nanowires we find an increase in electron density, which can be related to the presence of an accumulation layer at the InAs/InP interface. However, compared to the surface accumulation layer in uncapped InAs, this electron density is much reduced. We suggest that the increase in the observed field-effect mobility can be attributed to an increase of conduction through the inner part of the nanowire and a reduction of the contribution of electrons from the low-mobility accumulation layer. Furthermore the shell around the InAs reduces the surface roughness scattering and ionized impurity scattering in the nanowire.Kavli Institute of NanoscienceApplied Science
Tuning Edge States in Strained-Layer InAs/GaInSb Quantum Spin Hall Insulators
No full textWe report on a class of quantum spin Hall insulators (QSHIs) in strained-layer InAs/GaInSb quantum wells, in which the bulk gaps are enhanced up to fivefold as compared to the binary InAs/GaSb QSHI. Remarkably, with consequently increasing edge velocity, the edge conductance at zero and applied magnetic fields manifests time reversal symmetry-protected properties consistent with the Z(2) topological insulator. The InAs/GaInSb bilayers offer a much sought-after platform for future studies and applications of the QSHI.NSF [DMR-1508644]; Welch Foundation [C-1682]; National Basic Research Program of China (NBRPC) [2014CB920901]; NSFC [11434010]; NBRPC [2015CB921503]; RCQM, Rice UniversitySCI(E)ARTICLE511
Band-inverted gaps in InAs/GaSb and GaSb/InAs core-shell nanowires
No full textThe [111]-oriented InAs/GaSb and GaSb/InAs core-shell nanowires have been studied by the 8 x 8 Luttinger-Kohn (k) over right arrow center dot (p) over right arrow. Hamiltonian to search for non-vanishing fundamental gaps between inverted electron and hole bands. We focus on the variations of the band-inverted fundamental gap, the hybridization gap, and the effective gap with the core radius and shell thickness of the nanowires. The evolutions of all the energy gaps with the structural parameters are shown to be dominantly governed by the effect of quantum confinement. With a fixed core radius, a band-inverted fundamental gap exists only at intermediate shell thicknesses. The maximum band-inverted gap found is similar to 4.4 meV for GaSb/InAs and similar to 3.5 meV for InAs/GaSb core-shell nanowires, and for the GaSb/InAs core-shell nanowires the gap persists over a wider range of geometrical parameters. The intrinsic reason for these differences between the two types of nanowires is that in the shell the electron-like states of InAs is more delocalized than the hole-like state of GaSb, while in the core the hole-like state of GaSb is more delocalized than the electron-like state of InAs, and both favor a stronger electron-hole hybridization.Ministry of Science and Technology of China (MOST) through the National Key Basic Research Program of China [2012CB932703, 2012CB932700]; National Natural Science Foundation of China [91221202, 91421303, 61321001]; Swedish Research Council (VR)SCI(E)[email protected]
Ordered InAs nanodots formed on the patterned GaAs substrate by molecular beam epitaxy
No full textOrdered indium arsenide (InAs) nanodots are formed by molecular beam epitaxy (MBE) on patterned gallium arsenide (GaAs) substrates, which are prepared by implanting manganese (Mn) ions through anodic aluminum oxide (AAO) membranes into the GaAs wafers. Morphology and structure of the patterned GaAs substrate is determined both by the oxygen desorption and the Mn ion diffusion. Suitable patterned GaAs substrates with the same dosage of Mn ions for the following epitaxy can be obtained by controlling the deoxidization As(4) pressures during the oxygen desorption. Images of samples with different Mn ion implantation dosages and different molecular beam epitaxial conditions for the following deposition of InAs nanodots on the patterned GaAs substrates are characterized by atomic force microscopy (AFM). The order of the InAs nanodots is determined both by the AAO membrane and dosage of Mn ions. The density of InAs nanodots has great relation to the pore density of the AAO. (C) 2011 Elsevier Ltd. All rights reserved
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