  GeSn alloys offer a promising route towards a CMOS compatible light source
and the realization of electronic-photonic integrated circuits. One tactic to
improve the lasing performance of GeSn lasers is to use a high Sn content,
which improves the directness. Another popular approach is to use a low to
moderate Sn content with either compressive strain relaxation or tensile strain
engineering, but these strain engineering techniques generally require optical
cavities to be suspended in air, which leads to poor thermal management. In
this work, we develop a novel dual insulator GeSn-on-insulator (GeSnOI)
material platform that is used to produce strain-relaxed GeSn microdisks stuck
on a substrate. By undercutting only one insulating layer (i.e., Al2O3), we
fabricate microdisks sitting on SiO2, which attain three key properties for a
high-performance GeSn laser: removal of harmful compressive strain, decent
thermal management, and excellent optical confinement. We believe that an
increase in the Sn content of GeSn layers on our platform can allow achieving
improved lasing performance.
