  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.
