Self-Assembly of InAs Nanostructures on the Sidewalls of GaAs Nanowires Directed by a Bi Surfactant

Abstract

Surface energies play a dominant role in the self-assembly of three dimensional (3D) nanostructures. In this letter, we show that using surfactants to modify surface energies can provide a means to externally control nanostructure self-assembly, enabling the synthesis of novel hierarchical nanostructures. We explore Bi as a surfactant in the growth of InAs on the {110} sidewall facets of GaAs nanowires. The presence of surface Bi induces the formation of InAs 3D islands by a process resembling the StranskiKrastanov mechanism, which does not occur in the absence of Bi on these surfaces. The InAs 3D islands nucleate at the corners of the {110} facets above a critical shell thickness and then elongate along 110 directions in the plane of the nanowire sidewalls. Exploiting this growth mechanism, we realize a series of novel hierarchical nanostructures, ranging from InAs quantum dots on single {110} nanowire facets to zig-zag shaped nanorings completely encircling nanowire cores. Photoluminescence spectroscopy and cathodoluminescence spectral line scans reveal that small surfactant-induced InAs 3D islands behave as optically active quantum dots. This work illustrates how surfactants can provide an unprecedented level of external control over nanostructure self-assembly. KEYWORDS: nanowire, quantum dot, bismuth, surfactant, GaAs, semiconductor 2The bottom-up self-assembly of semiconductor nanostructures is directed by energy minimization. As a result, many aspects of nanostructure self-assembly are intrinsic and therefore difficult to control externally. For example, nanostructures such as nanowires (NWs) and quantum dots (QDs) spontaneously form low-energy facets during their synthesis. In the case of GaAs NWs grown by the Ga-assisted vapor-liquid-solid (VLS) mode, the sidewall facets are of {110} orientation. 1 This poses challenges for the realization of advanced hierarchical structures, such as QDs embedded within NWs, 2,3 since two-dimensional (2D) layer growth is always favored on GaAs{110} surfaces and three-dimensional (3D) islands do not form by the StranskiKrastanov (SK) mechanism. 2,4-6 The SK growth of InAs 3D islands on these surfaces has been observed after covering the facets with a thin AlAs layer, but, this is undesirable for most applications. 2,7 In contrast, GaAs NWs synthesized by Au-catalyzed growth typically exhibit {112} sidewall facets and the SK mechanism does occur on these surfaces, 6,8 however, the presence of Au can be detrimental to NW optoelectronic properties. 9 We recently reported that the presence of surface Bi can induce the self-assembly of InAs 3D islands directly on planar GaAs(110) surfaces. 10 The Bi surfactant was shown to modify the surface energies, reducing the energetic cost of 3D island formation. Furthermore, in contrast to more common surface-segregating elements like Sb and Te, which have been shown to reduce adatom diffusion and consequently inhibit the formation of 3D islands, 11,12 Bi has been found to increase adatom diffusion. 13 This makes Bi of particular i...

Bismuth-surfactant-induced growth and structure of InAs/GaAs(110) quantum dots

“…[5][6][7][8] Recently, we revealed that a surface-energy-modifying Bi surfactant can induce InAs QD formation on GaAs(110) planar surfaces and nanowire sidewalls, presenting a powerful new approach for externally directing QD formation. 9,10 Such InAs/GaAs(110) QDs are expected to exhibit a low Cs symmetry, and it has been predicted theoretically that strong in-plane piezoelectric fields in (110) QDs lead to linearly polarized emission associated with the ground state exciton. 11 Accordingly, recent photoluminescence (PL) experiments have indicated that emission from Bi-induced (110) QDs is linearly polarized.…”

Coaxial GaAs/(In,Ga)As Dot-in-a-Well Nanowire Heterostructures for Electrically Driven Infrared Light Generation on Si in the Telecommunication O Band

“…A Bi flux was supplied during the deposition of InAs to promote QD formation. 14,15 A 50 nm thick outer GaAs shell completes the confinement in the DWELL heterostructure. The total diameter of the DWELL NWs is approximately 220 nm.…”

“…A Bi flux at a beam equivalent pressure of 1.3×10 -6 mbar was supplied during InAs deposition in order to promote QD formation. 14,15 A 50 nm thick undoped GaAs shell grown under the same conditions completes the structure in order to provide carrier confinement in the DWELL region.…”

Tin Nanoparticles–Enhanced Optical Transportation in Branched CdS Nanowire Waveguides

“…The energy dispersive X‐ray (EDX) spectrum in the inset of Figure h shows that the main elemental composition of the expelled droplets is Sn. It should be noted that the CdS branched nanostructures without Sn particles are organized at the junctions, due to a different growth mechanism, which is the case for the well‐known Stranski–Krastanov mechanism, as shown in Figure S2 (Supporting Information). The Sn nanoparticles or islands are formed on the facets of the produced CdS nanowires and the secondary branches are the grafting growth on the micro‐backbone.…”