Impact of the growth strategy and device fabrication on the alloy homogeneity in optoelectronic grade Sn-rich GeSn

Highlights: • Homogeneous Sn distribution in GeSn micro-disks with very high Sn concentration. • SiGeSn buffer allows perfect GeSn micro-disks by providing better etching control. • First X-ray absorption spectroscopy on GeSn micro-disks with nanometre resolution. • Step-graded buffer avoids Sn segregation in GeSn thick layers with up to 16% of Sn. • Growth directly on Ge buffer generates Sn precipitation in high Sn-content layers. High Sn-content Ge_1-xSn_x alloys are excellent candidates for the fabrication of electronic and optoelectronic monolithically integrated devices on CMOS platforms. The fabrication of high performance devices requires high quality GeSn layers free of Sn precipitates. This work reports on the characterization of GeSn layers and micro-disk lasers with Sn concentrations ranging from 6 to 16% using synchrotron nano X-ray fluorescence mapping and nano X-ray absorption spectroscopy techniques. We demonstrate that the Sn precipitation observed in thick GeSn layers grown directly on Ge buffers can be fully suppressed, for Sn concentrations as high as 16%, with Ge_1-xSn_x step-graded buffers. The combination of optimal micro-disk fabrication parameters and full suppression of Sn precipitation can explain the superior lasing performance obtained in micro-disk lasers fabricated using such stacks.