Bi Incorporation and segregation in the MBE-grown GaAs-(Ga,Al)As-Ga(As,Bi) core-shell nanowires

TL;DR

This study investigates bismuth incorporation and segregation in GaAs-(Ga,Al)As-Ga(As,Bi) core-shell nanowires grown by molecular beam epitaxy, revealing how Bi flux influences shell smoothness, segregation, and the formation of branched nanowire structures.

Contribution

It demonstrates the effects of Bi flux on nanowire shell morphology and shows how Bi droplets can catalyze the growth of branched nanowire architectures.

Findings

Low Bi flux results in smooth shells with complete Bi incorporation.

Higher Bi flux causes Bi segregation and droplet formation on sidewalls.

Bi droplets can catalyze the growth of branches in nanowires.

Abstract

Incorporation of Bi into GaAs-(Ga,Al)As-Ga(As,Bi) core-shell nanowires grown by molecular beam epitaxy is studied with transmission electron microscopy. Nanowires are grown on GaAs(111)B substrates with Au-droplet assisted mode. Bi-doped shells are grown at low temperature (300 {\deg}C) with a close to stoichiometric Ga/As flux ratio. At low Bi fluxes, the Ga(As,Bi) shells are smooth, with Bi completely incorporated into the shells. Higher Bi fluxes (Bi/As flux ratio ~ 4%) led to partial segregation of Bi as droplets on the nanowires sidewalls, preferentially located at the nanowire segments with wurtzite structure. We demonstrate that such Bi droplets on the sidewalls act as catalysts for the growth of branches perpendicular to the GaAs trunks. Due to the tunability between zinc-blende and wurtzite polytypes by changing the nanowire growth conditions, this effect enables fabrication of branched nanowire architectures with branches generated from selected (wurtzite) nanowire segments.