  Recent demonstrations of optically pumped lasers based on GeSn alloys put
forward the prospect of efficient laser sources monolithically integrated on a
Si photonic platform. For instance, GeSn layers with 12.5% of Sn were reported
to lase at 2.5 um wavelength up to 130 K. In this work, we report a longer
emitted wavelength and a significant improvement in lasing temperature. The
improvements resulted from the use of higher Sn content GeSn layers of
optimized crystalline quality, grown on graded Sn content buffers using Reduced
Pressure CVD. The fabricated GeSn micro-disks with 13% and 16% of Sn showed
lasing operation at 2.6 um and 3.1 um wavelengths, respectively. For the
longest wavelength (i.e 3.1 um), lasing was demonstrated up to 180 K, with a
threshold of 377 kW/cm2 at 25 K.
