Structural Investigation of InAs-AlInAs and InAs-AlInP Core-Shell Nanowires

TL;DR

This study investigates the growth, structure, and defect characteristics of InAs nanowires with AlInAs and AlInP shells, revealing growth mode transitions and defect formation influenced by shell composition and strain.

Contribution

It demonstrates a method to grow uniform core-shell nanowires with controlled shell composition and elucidates the growth mechanisms and defect formation related to Al incorporation.

Findings

Addition of Al induces a transition from VLS to vapour-solid growth mode.

InAs-AlInP nanowires show misfit dislocations due to strain.

InAs-AlInAs nanowires are largely defect-free with lower strain.

Abstract

InAs nanowires were grown on GaAs substrates by the Au-assisted vapour-liquid-solid (VLS) method in a gas source molecular beam epitaxy (GS-MBE) system. Passivation of the InAs nanowires using InP shells proved difficult due to the tendency for the formation of axial rather than core-shell structures. To circumvent this issue, Al$_x$In$_{1-x}$As or Al$_x$In$_{1-x}$P shells with nominal Al composition fraction of x = 0.20, 0.36, or 0.53 were grown by direct vapour-solid deposition on the sidewalls of the InAs nanowires. Characterization by transmission electron microscopy revealed that the addition of Al in the shell resulted in a remarkable transition from the VLS to the vapour-solid growth mode with uniform shell thickness along the nanowire length. Possible mechanisms for this transition include reduced adatom diffusion, a phase change of the Au seed particle and surfactant effects. The InAs-AlInP core-shell nanowires exhibited misfit dislocations, while the InAs-AlInAs nanowires with lower strain appeared to be free of defects.