Strain engineering in Ge/GeSn core/shell nanowires

TL;DR

This study explores how strain influences the growth and defect formation in Ge/GeSn core/shell nanowires, revealing size-dependent effects on Sn incorporation and material quality crucial for mid-infrared optoelectronic applications.

Contribution

It provides a detailed analysis of strain effects on GeSn nanowire growth, combining experimental observations with finite element simulations to understand defect formation and material properties.

Findings

Smaller cores yield homogeneous GeSn shells

Larger cores lead to defects and segregation

Strain relaxation depends on core and shell sizes

Abstract

Strain engineering in Sn-rich group IV semiconductors is a key enabling factor to exploit the direct band gap at mid-infrared wavelengths. Here, we investigate the effect of strain on the growth of GeSn alloys in a Ge/GeSn core/shell nanowire geometry. Incorporation of Sn content in the 10-20 at.% range is achieved with Ge core diameters ranging from 50nm to 100nm. While the smaller cores lead to the formation of a regular and homogeneous GeSn shell, larger cores lead to the formation of multi-faceted sidewalls and broadened segregation domains, inducing the nucleation of defects. This behavior is rationalized in terms of the different residual strain, as obtained by realistic finite element method simulations. The extended analysis of the strain relaxation as a function of core and shell sizes, in comparison with the conventional planar geometry, provides a deeper understanding of the role of strain in the epitaxy of metastable GeSn semiconductors.