Inhomogeneous Si-doping of gold-seeded InAs nanowires grown by molecular beam epitaxy (original) (raw)
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On the growth of InAs nanowires by molecular beam epitaxy
Journal of Crystal Growth, 2011
The growth of InAs nanowires by molecular beam epitaxy only takes place in a narrow temperature range, independent of the method used to induce the growth: with (Au or Mn) or without metal catalysts. Our findings suggest that the physical chemistry of the intermetallic compound formed during the catalyzed growth of the NWs is not relevant for the induction of the growth. Moreover, the lattice structure of the wires always shows wurtzite sections. Our results indicate the need of a unified model for the metal-catalyzed and self-catalyzed growth of nanowires.
Alloy formation during molecular beam epitaxy growth of Si-doped InAs nanowires on GaAs[111]B
Journal of Applied Crystallography, 2013
Vertically aligned InAs nanowires (NWs) doped with Si were grown self-assisted by molecular beam epitaxy on GaAs[111]B substrates covered with a thin SiO x layer. Using out-of-plane X-ray diffraction, the influence of Si supply on the growth process and nanostructure formation was studied. It was found that the number of parasitic crystallites grown between the NWs increases with increasing Si flux. In addition, the formation of a Ga0.2In0.8As alloy was observed if the growth was performed on samples covered by a defective oxide layer. This alloy formation is observed within the crystallites and not within the nanowires. The Ga concentration is determined from the lattice mismatch of the crystallites relative to the InAs nanowires. No alloy formation is found for samples with faultless oxide layers.
Self-induced growth of vertical free-standing InAs nanowires on Si(111) by molecular beam epitaxy
Nanotechnology, 2010
We report self-induced growth of vertically aligned (i.e. along the [111] direction), free-standing InAs nanowires on Si(111) substrates by solid-source molecular beam epitaxy. Implementation of an ultrathin amorphous SiO x mask on Si(111) facilitated epitaxial InAs nanowire growth, as confirmed by high-resolution x-ray diffraction 2θ-ω scans and transmission electron microscopy. Depending on growth temperature (in the range of 400-520 • C) substantial size variation of both nanowire length and diameter was found under preservation of uniform, non-tapered hexagon-shaped geometries. The majority of InAs nanowires exhibited phase-pure zinc blende crystal structure with few defective regions consisting of stacking faults. Photoluminescence spectroscopy at 20 K revealed peak emission of the InAs nanowires at 0.445 eV, which is ∼30 meV blueshifted with respect to the emission of the bulk InAs reference due to radial quantum confinement effects. These results show a promising route towards integration of well-aligned, high structural quality InAs-based nanowires with the desired aspect ratio and tailored emission wavelengths on an Si platform.
Effect of Si-doping on InAs nanowire transport and morphology
Journal of Applied Physics, 2011
The effect of Si-doping on the morphology, structure, and transport properties of nanowires was investigated. The nanowires were deposited by selective-area metal organic vapor phase epitaxy in an N 2 ambient. It is observed that doping systematically affects the nanowire morphology but not the structure of the nanowires. However, the transport properties of the wires are greatly affected. Room-temperature four-terminal measurements show that with an increasing dopant supply the conductivity monotonously increases. For the highest doping level the conductivity is higher by a factor of 25 compared to only intrinsically doped reference nanowires. By means of back-gate field-effect transistor measurements it was confirmed that the doping results in an increased carrier concentration. Temperature dependent resistance measurements reveal, for lower doping concentrations, a thermally activated semiconductor-type increase of the conductivity. In contrast, the nanowires with the highest doping concentration show a metal-type decrease of the resistivity with decreasing temperature. V
Growth of vertical InAs nanowires on heterostructured substrates
Nanotechnology, 2009
We demonstrate the Au-assisted growth of semiconductor nanowires on different engineered substrates. Two relevant cases are investigated: GaAs/AlGaAs heterostructures capped by a 50 nmthick InAs layer grown by molecular beam epitaxy and a 2 µm-thick InAs buffer layer on Si(111) obtained by vapor phase epitaxy. Morphological and structural properties of substrates and nanowires are analyzed by atomic force and transmission electron microscopy. Our results indicate a promising direction for the integration of III-V nanostructures on Si-based electronics as well as for the development of novel micromechanical structures.
Photoluminescence properties of InAs nanowires grown on GaAs and Si substrates
Nanotechnology, 2010
We report the first photoluminescence (PL) characterization of InAs nanowires (NWs). The InAs NWs were grown on GaAs(111) B and Si(111) substrates using the Au-assisted molecular beam epitaxy (MBE) growth technique or metal-organic chemical vapor deposition (MOCVD). We compared the PL response of four samples grown under different conditions using MBE or MOCVD. High-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) patterns were utilized to determine the crystal structure and growth directions of the NWs to relate PL features to NW structural parameters. We observed mainly three PL peaks which were below, near and above InAs bandgaps, respectively. Temperature and excitation intensity dependence PL measurements were also performed to help elucidate the origins of the PL peaks of NWs. Of particular interest was a band-edge emission peak that was blue-shifted due to quantization effects of the InAs NWs, as confirmed by our calculation.
Experimental determination of adatom diffusion lengths for growth of InAs nanowires
Journal of Crystal Growth, 2013
Au-assisted InAs nanowires are grown using molecular beam epitaxy. By tailoring the growth and position of InAs nanowires, experimental values for the effective diffusion lengths of adatoms on both the substrate and nanowire sidewalls have been deduced. In the framework of a mass continuity growth model for group III elements, based on a simple kinetic but informative treatment without use of thermodynamic parameters, both shadowing effects and shared substrate diffusion areas are included. The growth model is fitted to two types of data, one for nanowires positioned in a quadratic array with varying pitch, and one for nanowires with axial heterostructures. For the given growth conditions the effective diffusion length for In adatoms on InAs NW sidewalls with wurtzite crystal structure is found to be 3 mm, whereas the effective diffusion of Ga adatoms is an order of magnitude smaller. The minimum pitch to ensure independent growth, without influence from nearby NWs, is found to be around 2 mm.
Large-area, catalyst-free heteroepitaxy of InAs nanowires on Si by MOVPE
Physica Status Solidi (A) Applications and Materials Science, 2011
In this paper, we show the results of experiments of InAs nanowire (NW) growth on (111)-oriented Si wafers. The NWs, grown at 620 8C by metal-organic vapor-phase epitaxy, are vertically aligned and $30 nm in diameter. Their structural properties are studied by transmission electron microscopy, evidencing a polytypic character, and the vibrational properties by Raman spectroscopy. An assessment of their electrical transport properties is carried out by measuring back-gated, single InAs NW field-effect transistors. The absence of a catalyst ensures the compatibility of the NW growth process with current CMOS technology.
Influence of the oxide layer for growth of self-assisted InAs nanowires on Si(111)
Nanoscale Research Letters, 2011
The growth of self-assisted InAs nanowires (NWs) by molecular beam epitaxy (MBE) on Si(111) is studied for different growth parameters and substrate preparations. The thickness of the oxide layer present on the Si(111) surface is observed to play a dominant role. Systematic use of different pre-treatment methods provides information on the influence of the oxide on the NW morphology and growth rates, which can be used for optimizing the growth conditions. We show that it is possible to obtain 100% growth of vertical NWs and no parasitic bulk structures between the NWs by optimizing the oxide thickness. For a growth temperature of 460°C and a V/III ratio of 320 an optimum oxide thickness of 9 ± 3 Å is found.
Controlled Synthesis of Phase-Pure InAs Nanowires on Si(111) by Diminishing the Diameter to 10 nm
Nano Letters, 2014
Here we report the growth of phase-pure InAs nanowires on Si (111) substrates by molecular-beam epitaxy using Ag catalysts. A conventional one-step catalyst annealing process is found to give rise to InAs nanowires with diameters ranging from 4.5 to 81 nm due to the varying sizes of the Ag droplets, which reveal strong diameter dependence of the crystal structure. In contrast, a novel two-step catalyst annealing procedure yields vertical growth of highly uniform InAs nanowires ∼10 nm in diameter. Significantly, these ultrathin nanowires exhibit a perfect wurtzite crystal structure, free of stacking faults and twin defects. Using these high-quality ultrathin InAs nanowires as the channel material of metal-oxide-semiconductor field-effect transistor, we have obtained a high I ON /I OFF ratio of ∼10 6 , which shows great potential for application in future nanodevices with low power dissipation.