Phase Control Growth of InAs Nanowires by Using Bi Surfactant (original) (raw)

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.

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.

Nanowire-Induced Wurtzite InAs Thin Film on Zinc-Blende InAs Substrate

Advanced Materials, 2009

Synthesis of materials with a desired crystal structure is a major challenge in materials engineering. Single-crystal thin films grown by epitaxy typically adopt the same crystal structure as that of their substrates. Here, we report on the observation of a wurtzite InAs thin-film structure on a zinc-blende InAs substrate. Electron-backscatter diffraction (EBSD) and transmission electron microscopy (TEM) confirm the wurtzite crystal structure. The bandgap of wurtzite InAs, obtained by low-temperature photoluminescence, is found to be 20% higher than that of zinc-blende InAs, in good agreement with band-structure calculations. Microscopy studies suggest that the wurtzite InAs thin film is the result of step flow along the surface from the base of wurtzite InAs nanowires synthesized by chemical beam epitaxy on a zinc-blende InAs substrate, leading to layer-by-layer lateral expansion. Although the conditions for the controlled growth of wurtzite InAs films need to be investigated, our observations suggest a new approach to creating thin films with nanowire-induced crystal structure. The creation and integration of a material with different crystal structures, such as polymorphism and the associated heterocrystalline heterostructures, could open up new opportunities in bandgap engineering and related device applications. COMMUNICATION www.advmat.de

Optical emission of InAs nanowires

Nanotechnology, 2012

Wurtzite InAs nanowire samples grown by chemical beam epitaxy have been analyzed by photoluminescence spectroscopy. The nanowires exhibit two main optical emission bands at low temperatures. They are attributed to the recombination of carriers in quantum well structures, formed by zincblende-wurtzite alternating layers, and to the donor-acceptor pair. The blue-shift observed in the former emission band when the excitation power is increased is in good agreement with the type-II band alignment between the wurtzite and zincblende sections predicted by previous theoretical works. When increasing the temperature and the excitation power successively, an additional band attributed to the band-to-band recombination from wurtzite InAs appears. We estimated a lower bound for the wurtzite band gap energy of approximately 0.46 eV at low temperature.

Growth of InAs Wurtzite Nanocrosses from Hexagonal and Cubic Basis

Epitaxially connected nanowires allow for the design of electron transport experiments and applications beyond the standard two terminal device geometries. In this Letter, we present growth methods of three distinct types of wurtzite structured InAs nanocrosses via the vapor−liquid−solid mechanism. Two methods use conventional wurtzite nanowire arrays as a 6-fold hexagonal basis for growing single crystal wurtzite nanocrosses. A third method uses the 2-fold cubic symmetry of (100) substrates to form well-defined coherent inclusions of zinc blende in the center of the nanocrosses. We show that all three types of nanocrosses can be transferred undamaged to arbitrary substrates, which allows for structural, compositional, and electrical characterization. We further demonstrate the potential for synthesis of as-grown nanowire networks and for using nanowires as shadow masks for in situ fabricated junctions in radial nanowire heterostructures.

Exploring the band structure of Wurtzite InAs nanowires using photocurrent spectroscopy

Nano Research, 2020

We use polarized photocurrent spectroscopy in a nanowire device to investigate the band structure of hexagonal Wurtzite InAs. Signatures of optical transitions between four valence bands and two conduction bands are observed which are consistent with the symmetries expected from group theory. The ground state transition energy identified from photocurrent spectra is seen to be consistent with photoluminescence emitted from a cluster of nanowires from the same growth substrate. From the energies of the observed bands we determine the spin orbit and crystal field energies in Wurtzite InAs. This information is essential to the development of crystal phase engineering of this important III-V semiconductor.

Effects of dangling bonds and diameter on the electronic and optical properties of InAs nanowires

In this article we explore the effects of dangling bonds and diameter on the electronic properties of the wurtzite InAs nanowires (NWs) using the density functional theory. The NWs are confined in the hexagonal supercell and are simulated in the [0001] direction. The calculations have been carried out by applying the periodic boundary conditions along the NW axis, i.e., z-Cartesian coordinate, providing enough vacuum to isolate the system from its neighbors. The optical properties of a material are directly related to the band-gap; therefore a relationship between the band-gap and diameter of the nanowires is obtained by using two models, where the band-gap for a larger diameter NW can be estimated. The results of these models are compared with each other and the effects of the dangling bonds on the band-gaps are also investigated. The band-gap of the nanowires decreases and the dangling bond ratio increases with the increase in the diameter of the nanowire, and hence we expect that for large diameter nanowires the band-gap will approach the band gap of the bulk material. An interesting feature of the shift in the band-gap from indirect to direct, i.e. optically inactive to active, is also observed in these NWs with the increase in the diameter.

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.