Facet-Selective Growth on Nanowires Yields Multi-Component Nanostructures and Photonic Devices

Abstract

Enhanced synthetic control of the morphology, crystal structure, and composition of nanostructures can drive advances in nanoscale devices. Axial and radial semiconductor nanowires are examples of nanostructures with one and two structural degrees of freedom, respectively, and their synthetically tuned and modulated properties have led to advances in nanotransistor, nanophotonic, and thermoelectric devices. Similarly, developing methods that allow for synthetic control of greater than two degrees of freedom could enable new opportunities for functional nanostructures. Here we demonstrate the first regioselective nanowire shell synthesis in studies of Ge and Si growth on faceted Si nanowire surfaces. The selectively deposited Ge is crystalline and its facet position can be synthetically controlled in situ. We use this synthesis to prepare electrically-addressable nanocavities into which solution soluble species such as Au nanoparticles can be incorporated. The method furnishes multi-component nanostructures with unique photonic properties and presents a more sophisticated nanodevice platform for future applications in catalysis and photodetection.Semiconductor nanowires (NWs) represent a diverse class of nanomaterials whose synthetically-tunable structural, electronic, and optical properties 1-3 have enabled active nanodevices including high-performance field-effect transistors, 4 ultra-sensitive biological probes, 5-7 and solar cells and photonic devices with tunable optical spectra. [8][9][10][11][12] NWs can be classified according to the number of degrees of freedom (DoF) they possess, which represent fundamental physical coordinates along which their structure can be manipulated. Axial and radial (core/shell) modulated NWs have 1 and 2 DoF, respectively, and have been extensively studied and characterized. 2,[13][14][15][16][17][18][19] Nevertheless, the properties of nanostructures possessing greater complexity and anisotropy have not been determined.A nanostructure with 3 DoF and higher can be realized by breaking the rotational symmetry of conventional radial shell growth ( Figure 1A). A high-resolution scanning electron micrograph (SEM) of a faceted core/shell Si NW ( Figure 1B) reveals well-defined surfaces that were previously indexed 9 as {111}, {011}, and {113}. NWs with this same morphology and set of surface facets serve as the faceted templates from which all subsequent nanostructures in this study are grown. Following chemical vapor deposition (CVD) synthesis of the SiNW templates, 9 introduction of GeH 4 and H 2 at lower tem- perature and pressure into the same reactor (Supporting Information) yields a new product featuring selective material deposition on the {111} and {011} Si surface facets ( Figure 1B). Energy dispersive x-ray spectroscopy (EDS) performed on the nanostructure ( Figure 1C) confirms the elemental identity of the deposited material as Ge and reveals that facet selectivity is preserved along the length of the nanostructure. A planview transmission electron micrograph (...

Antimony Induced {112}A Faceted Triangular GaAs1−xSbx/InP Core/Shell Nanowires and Their Enhanced Optical Quality

“…The EDX map demonstrates the selective growth of InP shell, resulting in poor coverage of InP on the GaAs 0.56 Sb 0.44 core along the 〈112〉A directions. This facet‐selective growth has been demonstrated for radial inclusion of different quantum structures in both group IV and III–V semiconductor nanowire systems . Figure c compares the EDX spectrum of the core and shell.…”

Selective GaSb radial growth on crystal phase engineered InAs nanowires

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Si‐core/SiGe‐shell channel nanowire FET for sub‐10‐nm logic technology in the THz regime

“…However, for the core/shell nanowire structure, the critical thickness is larger than that of the planar growth, which reduces the burden in terms of the selection of the thickness and Ge fraction of the shell layer . Furthermore, conformal and either a single‐like or polycrystalline shell layer can be obtained by choosing the appropriate gas‐phase species, employing a vapor‐liquid‐solid chemical vapor deposition (VLSCVD), adopting the nucleation properties of Ge adatoms on the Si facets, and making the core structure similar to a circle . With respect to the gate stack, a Si‐capping layer and post‐deposition annealing (PDA) can be solutions for higher mobility and a reduced gate leakage current .…”