  GeSn alloys are nowadays considered as the most promising materials to build
Group IV laser sources on silicon (Si) in a full complementary metal oxide
semiconductor-compatible approach. Recent GeSn laser developments rely on
increasing the band structure directness, by increasing the Sn content in thick
GeSn layers grown on germanium (Ge) virtual substrates (VS) on Si. These lasers
nonetheless suffer from a lack of defect management and from high threshold
densities. In this work we examine the lasing characteristics of GeSn alloys
with Sn contents ranging from 7 \% to 10.5 \%. The GeSn layers were patterned
into suspended microdisk cavities with different diameters in the 4-\SI{8
}{\micro\meter} range. We evidence direct band gap in GeSn with 7 \% of Sn and
lasing at 2-\SI{2.3 }{\micro\meter} wavelength under optical injection with
reproducible lasing thresholds around \SI{10
}{\kilo\watt\per\square\centi\meter}, lower by one order of magnitude as
compared to the literature. These results were obtained after the removal of
the dense array of misfit dislocations in the active region of the GeSn
microdisk cavities. The results offer new perspectives for future designs of
GeSn-based laser sources.
