Early stages of GaAs nanowires VLS self-catalyzed growth on silica-terminated silicon substrate: A photoemission study

TL;DR

This study investigates the initial stages of GaAs nanowire growth on silica-terminated silicon substrates using MBE, revealing how Ga nano-droplets interact with the silica layer and facilitate epitaxial growth through detailed spectroscopic and microscopic analysis.

Contribution

It provides new insights into the early VLS growth process of GaAs nanowires on silicon, highlighting the role of Ga nano-droplets and silica layer interactions in nucleation and growth.

Findings

Ga nano-droplets drill through silica overlayer to contact silicon

High annealing temperature reduces SiOx, forming holes for nucleation

Three chemical environments of Ga identified during growth

Abstract

In this paper the early stages of the self-catalyzed Vapor-Liquid-Solid (VLS) growth of GaAs nanowires on epi-ready Si substrates by Molecular Beam Epitaxy (MBE) are studied. The interaction of Ga nano-droplets (NDs) with the silica overlayer is investigated by X-ray Photoemission Spectroscopy (XPS) and Atomic Force Microscopy (AFM). We show how Ga NDs drill the silica overlayer and make contact with bulk Si to allow GaAs nanowires (NWs) epitaxial growth by studying each of the three steps of the NW growth process sequentially: Ga NDs pre-deposition, post-deposition annealing to reach the NW growth temperature, and finally NW growth itself. The pre-deposition temperature allows to control the density and morphology of the NDs. A high enough annealing temperature enhances the reduction of SiOx by Ga oxidation and leads to the formation of holes which is seen by a new component in XPS spectra, assumed to be the consequence of the Ga-Si interaction. Finally, these nano-holes act as nucleation sites for the epitaxial GaAs VLS growth. During the GaAs growth, three different chemical environments of Ga are identified in Ga2p core level: metallic Ga due to the droplets at the top of the NWs, Ga oxide in contact with the SiOx overlayer and Ga arsenide from NWs.