Structural investigation of GaInP nanowires using X-ray diffraction

AbstractIn this work the structure of ternary GaxIn1−xP nanowires is investigated with respect to the chemical composition and homogeneity. The nanowires were grown by metal–organic vapor-phase epitaxy. For the investigation of ensemble fluctuations on several lateral length scales, X-ray diffraction reciprocal space maps have been analyzed. The data reveal a complicated varying materials composition across the sample and in the nanowires on the order of 20%. The use of modern synchrotron sources, where beam-sizes in the order of several 10μm are available, enables us to investigate compositional gradients along the sample by recording diffraction patterns at different positions. In addition, compositional variations were found also within single nanowires in X-ray energy dispersive spectroscopy measurements

Epitaxial growth of III-V nanowires on group IV substrates

Semiconducting nanowires are emerging as a route to combine heavily mismatched materials. The high level of control on wire dimensions and chemical composition makes them promising materials to be integrated in future silicon technologies as well as to be the active element in optoelectronic devices. In this article, we review the recent progress in epitaxial growth of nanowires on non-corresponding substrates. We highlight the advantage of using small dimensions to facilitate accommodation of the lattice strain at the surface of the structures. More specifically, we will focus on the growth of III–V nanowires on group IV substrates. This approach enables the integration of high-performance III–V semiconductors monolithically into mature silicon technology, since fundamental issues of III–V integration on Si such as lattice and thermal expansion mismatch can be overcome. Moreover, as there will only be one nucleation site per crystallite, the system will not suffer from antiphase boundaries. Issues that affect the electronic properties of the heterojunction, such as the crystallographic quality and diffusion of elements across the heterointerface will be discussed. Finally, we address potential applications of vertical III–V nanowires grown on silicon

Epitaxial growth of III–V nanowires on group IV substrates

Semiconducting nanowires are emerging as a route to combine heavily mismatched materials. The high level of control on wire dimensions and chemical composition makes them promising materials to be integrated in future silicon technologies as well as to be the active element in optoelectronic devices. This article reviews the recent progress in epitaxial growth of nanowires on non-corresponding substrates. We highlight the advantage of using small dimensions to facilitate accommodation of the lattice strain at the surface of the structures. More specifically, we will focus on the growth of III–V nanowires on Group IV substrates. This approach enables the integration of high-performance III–V semiconductors monolithically into mature silicon technology, since fundamental issues of III–V integration on Si such as lattice and thermal expansion mismatch can be overcome. Moreover, as there will only be one nucleation site per crystallite, the system will not suffer from antiphase boundaries. Issues that affect the electronic properties of the heterojunction, such as the crystallographic quality and diffusion of elements across the heterointerface, will be discussed. Finally, we address potential applications of vertical III–V nanowires grown on silicon

Synergetic nanowire growth

Interest in nanowires continues to grow because they hold the promise of monolithic integration of high-performance semiconductors with new functionality into existing silicon technology. Most nanowires are grown using vapour-liquid-solid growth, and despite many years of study this growth mechanism remains under lively debate. In particular, the role of the metal particle is unclear. For instance, contradictory results have been reported on the effect of particle size on nanowire growth rate. Additionally, nanowire growth from a patterned array of catalysts has shown that small wire-to-wire spacing leads to materials competition and a reduction in growth rates. Here, we report on a counterintuitive synergetic effect resulting in an increase of the growth rate for decreasing wire-to-wire distance. We show that the growth rate is proportional to the catalyst area fraction. The effect has its origin in the catalytic decomposition of precursors and is applicable to a variety of nanowire materials and growth techniques

Interface study on heterostructured GaP-GaAs nanowires

The interface chemical composition of heterostructured GaP-GaAs nanowire segments was studied by the use of energy-dispersive x-ray analysis. An arsenic-rich tail in the GaP segments following GaAs could be minimized by reducing the AsH3 molar fraction and the growth rate. For the temperature regime used for vapour-liquid-solid growth, we observe the opposite trend on interface sharpness compared to high-temperature layer-by-layer growth, that is, the sharpness of the interface improves with reducing temperature

Growth kinetics of heterostructured GaP-GaAs nanowires

We have studied the vapor-liquid-solid (VLS) growth dynamics of GaP and GaAs in heterostructured GaP-GaAs nanowires. The wires containing multiple GaP-GaAs junctions were grown by the use of metal-organic vapor phase-epitaxy (MOVPE) on SiO2, and the lengths of the individual sections were obtained from transmission electron microscopy. The growth kinetics has been studied as a function of temperature and the partial pressures of the precursors. We found that the growth of the GaAs sections is limited by the arsine (AsH3) as well as the trimethylgallium (Ga(CH 3)3) partial pressures, whereas the growth of GaP is a temperature-activated, phosphine(PH3)-limited process with an activation energy of 115 ± 6 kJ/mol. The PH3 kinetics obeys the Hinshelwood-Langmuir mechanism, indicating that the dissociation reaction of adsorbed PH3 into PH2 and H on the catalytic gold surface is the rate-limiting step for the growth of GaP. In addition, we have studied the competitive thin layer growth on the sidewalls of the nanowires. Although the rate of this process is 2 orders of magnitude lower than the growth rate of the VLS mechanism, it competes with VLS growth and results in tapered nanowires at elevated temperatures. © 2006 American Chemical Society. U7 - Export Date: 2 August 2010 U7 - Source: Scopu

Tunable double quantum dots in InAs nanowires

Semiconductor nanowires offer a very versatile approach to create tunable quantum dots. Of the different semiconductor materials that can be grown as nanowires, InAs is particularly interesting due to the large spin-orbit coupling and furthermore promising for devices due to the comparably easy processing for Ohmic contacts. Here we study the electronic transport through gateable InAs nanowire devices at low temperatures. The nanowires are grown by MOVPE, and horizontal devices are individually fabricated using electron-beam lithography. We use local top gates to create barriers that can be used to define tunable quantum dots. Towards our final goal of spin manipulation of single electrons, we focus on tunable double dots. We measure the electronic transport through double quantum dots for the different accessible regimes: we present stability diagrams that demonstrate the tunability from two independent dots to one combined dot, including the particularly interesting region of two interacting quantum dots

Towards vertical III-V nanowire devices

Investigation and understanding of growth parameters determining nanowire growth rates is necessary. For vertical architecture design relying on closely-spaced nanowire-based devices, absolute control of growth rates and wire (device) dimensions is required. Heterostructured nanowires where the segment dimensions critically determine quantization effects and thus the (opto) electronic properties of the wires were synthesized

Modification of the photoluminescence anisotropy of semiconductor nanowires by coupling to surface plasmon polaritons

We demonstrate efficient modification of the polarized light emission from single semiconductor nanowires by coupling this emission to surface plasmon polaritons on a metal grating. The polarization anisotropy of the emitted photoluminescence from single nanowires is compared for wires deposited on silica, a fiat gold film, and a shallow gold grating. By varying the orientation of the nanowire with respect to the grating grooves, the large intrinsic polarization anisotropy can be either suppressed or enhanced. This modification is interpreted by the appearance of an additional emission channel induced by surface plasmon polaritons and their conversion top-polarized radiation at the grating

Optical anisotropy of semiconductor nanowires

Semiconductor nanowires are novel nanostructures full of promise for optical applications. Nanowires have subwavelength diameters and large aspect ratios, which combined with the high permittivity of semiconductors lead to a strong optical anisotropy. We review in this chapter this optical anisotropy, focusing on the polarization anisotropy of the photoluminescence of individual nanowires and the propagation of light through birefringent ensembles of aligned nanowires. Recent developments in bottom-up nanofabrication techniques allow the growth of free-standing semiconductor nanowires with controlled composition, lateral dimensions of typically 10–100 nm, and lengths of several micrometers (see Fig. 6.1). The small lateral dimensions of nanowires enables to grow them heteroepitaxially onto different substrates [1–3] or even to design heterostructures with segments, shells, and/or quantum dots of different semiconductors in a single nanowire [4–8]. Nanowires are full of promise for monolithic integration of high-performance semiconductors with new functionality [8–11] into existing silicon technology [2, 3, 12]. These nanostructures will offer new possibilities as next generation of optical and optoelectronical components. Junctions in semiconductor nanowires and light emitting devices have been demonstrated [4, 13–17]. Although the quantum efficiency of these nano-LEDs is still low, fast progress is being made on the passivation of the nanowire surface and the increase of their efficiency [18, 19]. Also, optically and electrically driven nanowire lasing have been reported [9, 20, 21]. Nanowires have been proposed as polarization sensitive photodetectors [22, 23] and as a source for single photons [8, 24]. The encouraging perspectives for novel applications has lead to improved control over nanowire synthesis and materials composition [4, 5, 25–27]. However, little is known about how light is emitted by individual nanowires or how light is scattered by ensembles of these nanostructures. The large geometrical anisotropy of nanowires and the high refractive index of semiconductors give rise to a huge optical anisotropy, which has been reported as a strongly polarized photoluminescence of individual nanowires along their long axis [22, 28]. In this chapter we review the polarization anisotropy in the photoluminescence of individual nanowires. We also describe the propagation of light through ensembles of nanowires oriented perpendicularly to the surface of a substrate. The controlled growth and alignment of the nanowires leads to a medium with giant birefringence [29], i.e., a medium with a large difference in refractive indexes for different polarizations. The giant birefringence in ensembles of nanowires can be easily tuned by changing the semiconductor filling fraction and is not restricted to narrow frequency bands as in periodic structures [30]. Broadband and giant birefringence constitutes an elegant example of the extreme optical anisotropy of nanowires, which may lead to nanoscale polarization controlling media [31], the efficient generation of nonlinear signals [32], and the observation of novel surface electromagnetic modes on birefringent materials [33]