Kinetic Control of Morphology and Composition in Ge/GeSn Core/Shell Nanowires

TL;DR

This study investigates how growth conditions affect the morphology and composition of Ge/GeSn core/shell nanowires, revealing a transition from hexagonal to dodecagonal shapes and enhanced Sn incorporation at specific facets, with implications for optoelectronic applications.

Contribution

The paper combines experimental, ab-initio, and phase-field modeling to elucidate the growth mechanisms and morphology control of Ge/GeSn nanowires, providing new insights into their structural and compositional tuning.

Findings

Morphology transitions from hexagonal to dodecagonal with increased Sn precursor.

Sn incorporation is favored at {112} surfaces due to tensile strain.

Photoluminescence tunability linked to composition and morphology changes.

Abstract

The growth of Sn-rich group-IV semiconductors at the nanoscale provides new paths for understanding the fundamental properties of metastable GeSn alloys. Here, we demonstrate the effect of the growth conditions on the morphology and composition of Ge/GeSn core/shell nanowires by correlating the experimental observations with a theoretical interpretation based on a multi-scale approach. We show that the cross-sectional morphology of Ge/GeSn core/shell nanowires changes from hexagonal to dodecagonal upon increasing the supply of the Sn precursor. This transformation strongly influences the Sn distribution as a higher Sn content is measured under the {112} growth front. Ab-initio DFT calculations provide an atomic-scale explanation by showing that Sn incorporation is favored at the {112} surfaces, where the Ge bonds are tensile-strained. A phase-field continuum model was developed to reproduce the morphological transformation and the Sn distribution within the wire, shedding light on the complex growth mechanism and unveiling the relation between segregation and faceting. The tunability of the photoluminescence emission with the change in composition and morphology of the GeSn shell highlights the potential of the core/shell nanowire system for opto-electronic devices operating at mid-infrared wavelengths.