Synthesis of strain-relaxed Ge-Sn alloys using ion implantation and pulsed laser melting

TL;DR

This study demonstrates a scalable method to synthesize highly-relaxed Ge-Sn alloys with significant Sn incorporation, overcoming strain-related limitations and enabling direct bandgap properties for optoelectronic applications.

Contribution

It introduces a novel approach using ion implantation and pulsed laser melting to produce thick, strain-relaxed Ge-Sn alloys with high Sn content, advancing material quality and scalability.

Findings

Material is largely relaxed as confirmed by X-ray mapping.

Highest Sn concentration achieved is approximately 6 at.%.

Photoluminescence at 2045 nm indicates active Sn incorporation.

Abstract

Ge-Sn alloys with a sufficiently high concentration of Sn is a direct bandgap group IV material. Recently, ion implantation followed by pulsed laser melting has been shown to be a promising method to realize this material due to its high reproducibility and precursor-free process. A Ge-Sn alloy with ~9 at.% Sn was shown to be feasible by this technique. However, the compressive strain, inherently occurring in heterogeneous epitaxy of the film, evidently delays the material from the direct bandgap transition. In this report, an attempt to synthesize a highly-relaxed Ge-Sn alloy will be presented. The idea is to produce a significantly thicker film with a higher implant energy and doses. X-ray reciprocal space mapping confirms that the material is largely-relaxed. The peak Sn concentration of the highest dose sample is 6 at.% as determined by Rutherford backscattering spectrometry. Cross-sectional transmission electron microscopy shows unconventional defects in the film as the mechanism for the strain relaxation. Finally, a photoluminescence (PL) study of the strain-relaxed alloys shows photon emission at a wavelength of 2045 nm, suggesting an active incorporation of Sn concentration of ~6 at.%. The results of this study pave way to produce high quality relaxed GeSn alloy using an industrially scalable method.