Effect of catalyst diameter on vapour-liquid-solid growth of GaAs nanowires

Abstract

GaAs nanowires were grown on (111)B GaAs substrates using the vapour-liquid-solid (VLS) mechanism. The Au/Pt nanodots used to catalyse wire growth were defined lithographically and had varying diameter and separation. An in-depth statistical analysis of the resulting nanowires, which had a cone-like shape, was carried out.This revealed that there were two categories of nanowire present, with differing height and tapering angle.The bimodal nature of wire shape was found to depend critically on the diameter of the Au-Ga droplet atop the nanowire. Transmission Electron Microscopy (TEM) analysis also revealed that the density of stacking faults in the wires varied considerably between the two categories of wire. It is believed that the cause of the distinction in terms of shape and crystal structure is related to the contact angle between the droplet and the solid-liquid interface. The dependency of droplet diameter on contact angle is likely related to line-tension, which is a correction to Young's equation for the contact angle of a droplet upon a surface. The fact that contact angle may influence resulting wire structure and shape has important implications for the planning of growth conditions and the preparation of wires for use in proposed devices. a) Electronic mail: odowdbj@tcd.ie

Mass-transport driven growth dynamics of AlGaAs shells deposited around dense GaAs nanowires by metalorganic vapor phase epitaxy

“…where β is the contact angle formed at the triple-phase line of the Au droplet, the GaAs nanowire and the vapor, experimentally 90°≤ β ≤ 127°after growth, 25,26 with GaAs nanowires in the zincblend (ZB) phase having preference for higher contact angles (β ≅ 125°− 127°). As our GaAs nanowires exhibit pure ZB phase, 27 we set sin β = 0.81 in eqn (1).…”

Radial Growth of Self-Catalyzed GaAs Nanowires and the Evolution of the Liquid Ga-Droplet Studied by Time-Resolved in Situ X-ray Diffraction

“…axial NW heterostructures, 25 and for advanced device applications. [26][27][28] Hence, current efforts aim at the control, 5,7,[29][30][31] and understanding 8,9,[32][33][34][35][36][37][38][39][40][41] of radial growth processes responsible for tapering. Of particular interest here are self-stabilizing growth processes that are closely linked to the liquid Ga-droplet.…”

“…The size of the droplet correlates with the actual NW diameter. 5−10 Composition 11,12 and shape 5,13,14 of the droplet, and therefore its wetting conditions at the liquid− solid interface and the facets involved, determine the microstructure of the growing NW. 14−18 Regarding the wetting conditions, two different regimes can be identified.…”

“…In this process their morphology is strongly influenced by the liquid Ga-droplet at the NW tip. , This droplet acts as a catalyst for the uniaxial NW growth and at the same time as material reservoir. The size of the droplet correlates with the actual NW diameter. − Composition , and shape ,, of the droplet, and therefore its wetting conditions at the liquid–solid interface and the facets involved, determine the microstructure of the growing NW. − Regarding the wetting conditions, two different regimes can be identified. The zinc-blende (ZB) phase is favored for large wetting angles β ≈ 130°, whereas the wurtzite (WZ) phase is typically favored for wetting angles β ≈ 90°. ,− Usually, the transition of β between these two regimes is causing highly faulted segments .…”

“…On the one hand, tapering was first regarded as unintended side-effect due to, for example, an inflation of the droplet during growth, as a consequence of unbalanced material fluxes, and its minimization was desired . On the other hand, by harnessing radial growth processes, tapered NWs geometries could be exploited, for example, for axial NW heterostructures, and for advanced device applications. − Hence, current efforts aim at the control ,,− and understanding ,,− of radial growth processes responsible for tapering. Of particular interest here are self-stabilizing growth processes that are closely linked to the liquid Ga-droplet. , In addition to the radial growth processes involving the droplet (VLS), growth at the NW side-walls via the vapor–solid (VS) mode further influences the final shape of the NW ,,,, and impedes the direct observation of the aforementioned self-stabilization processes.…”