  GeSn alloys are promising candidates for complementary
metal-oxide-semiconductor (CMOS)-compatible, tunable lasers. Relaxation of
residual compressive strain in epitaxial GeSn has recently shown promise in
improving the lasing performance. However, the suspended device configuration
that has thus far been introduced to relax the strain is destined to limit heat
dissipation, thus hindering the device performance. Herein, we demonstrate that
strain-free GeSn microdisk laser devices fully released on Si outperform the
canonical suspended devices. This approach allows to simultaneously relax the
limiting compressive strain while offering excellent thermal conduction.
Optical simulations confirm that, despite a relatively small refractive index
contrast between GeSn and Si, optical confinement in strain-free GeSn optical
cavities on Si is superior to that in conventional strain-free GeSn cavities
suspended in the air. Moreover, thermal simulations indicate a negligible
temperature increase in our device. Conversely, the temperature in the
suspended devices increases substantially reaching, for instance, 120 K at a
base temperature of 75 K under the employed optical pumping conditions. Such
improvements enable increasing the operation temperature by ~40 K and reducing
the lasing threshold by 30%. This approach lays the groundwork to implement new
designs in the quest for room temperature GeSn lasers on Si.
