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

Abstract : High Sn-content Ge1-xSnx 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 Ge1-xSnx 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.