Self-assembly of InAs nanostructures on the sidewalls of GaAs nanowires directed by a Bi surfactant

TL;DR

This paper demonstrates how Bi surfactant modifies surface energies to control the self-assembly of InAs nanostructures on GaAs nanowire sidewalls, enabling the creation of novel hierarchical quantum dot structures.

Contribution

It introduces a surfactant-mediated growth mechanism to externally control nanostructure self-assembly, leading to new hierarchical InAs nanostructures on GaAs nanowires.

Findings

Bi induces InAs 3D island formation via Stranski-Krastanov mechanism.

InAs islands act as optically active quantum dots.

Hierarchical nanostructures like nanorings are achieved.

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 {1-10} 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 {1-10} 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 {1-10} 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.