Direct evidence of enhanced Ga interdiffusion in InAs vertically aligned free-standing nanowires (original) (raw)

Direct Evidences of Enhanced Ga Interdiffusion in InAs Vertically Aligned Free-Standing Nanowires

Journal of Nanoscience and Nanotechnology, 2009

We present direct evidence of enhanced Ga interdiffusion in InAs free-standing nanowires grown at moderate temperatures by molecular beam epitaxy on GaAs (111)B. Scanning electron microscopy together with X-ray diffraction measurements in coplanar and grazing incidence geometries show that nominally grown InAs NWs are actually made of In 0.86 Ga 0.14 As. Unlike typical vapor-liquid-solid growth, these nanowires are formed by diffusion-induced growth combined with strong interdiffusion from substrate material. Based on the experimental results, a simple nanowire growth model accounting for the Ga interdiffusion is also presented. This growth model could be generally applicable to the molecular beam heteroepitaxy of III-V 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.

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.

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.

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.

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.

Inhomogeneous Si-doping of gold-seeded InAs nanowires grown by molecular beam epitaxy

Applied Physics Letters, 2013

We have investigated in-situ Si doping of InAs nanowires grown by molecular beam epitaxy from gold seeds. The effectiveness of n-type doping is confirmed by electrical measurements showing an increase of the electron density with the Si flux. We also observe an increase of the electron density along the nanowires from the tip to the base, attributed to the dopant incorporation on the nanowire facets whereas no detectable incorporation occurs through the seed. Furthermore the Si incorporation strongly influences the lateral growth of the nanowires without giving rise to significant tapering, revealing the complex interplay between axial and lateral growth.

Growth mechanism of InAs–InSb heterostructured nanowires grown by chemical beam epitaxy

Journal of Crystal Growth, 2011

We report on the particle diameter dependence of the growth rate of the InSb segment of InAs-InSb heterostructured nanowires grown by chemical beam epitaxy. The analysis of the growth rate reveals that the growth is limited by the Gibbs-Thomson effect and the effect of NW lateral dimensions on the nucleation rate during the layer by layer growth. In the temperature range explored, the surface diffusion of adatoms toward the particle and the growth temperature are not affecting the growth rate.

Growth of III-V semiconductor nanowires by molecular beam epitaxy

Microelectronics Journal, 2009

We present here the growth of GaAs, InAs and InGaAs nanowires by molecular beam epitaxy. The nanowires have been grown on different substrates [GaAs(0 0 1), GaAs , SiO 2 and Si(111)] using gold as the growth catalyst. We show how the different substrates affect the results in terms of nanowire density and morphology. We also show that the growth temperature for the InGaAs nanowires has to be carefully chosen to obtain homogeneous alloys.

Understanding Self-Aligned Planar Growth of InAs Nanowires

Nano Letters, 2013

Semiconducting nanowires have attracted lots of attention because of their potential applications. Compared with free-standing nanowires, self-aligned planar nanowires grown epitaxially on the substrate have shown advantageous properties such as being twin defect free and ready for device fabrication, opening potentials for the large-scale device applications. Understanding of planar nanowire growth, which is essential for selective growth of planar vs freestanding wires, is still limited. In this paper, we reported different growth behaviors for self-aligned planar and free-standing InAs nanowires under identical growth conditions. We present a new model based on a revised Gibbs−Thomson equation for the planar nanowires. Using this model, we predicted and successfully confirmed through experiments that higher arsenic vapor partial pressure promoted free-standing InAs nanowire growth. A smaller critical diameter for planar nanowire growth was predicted and achieved experimentally. Successful control and understanding of planar and free-standing nanowire growth established in our work opens up the potential of large-scale integration of self-aligned nanowires for practical device applications.