Microstructuring to Improve the Thermal Stability of GeSn Layers

Tin segregation in Ge_1-xSn_x alloys is one of the major problems potentially hindering the use of this material in devices. Ge_1-xSn_x microdisks fabricated from layers with Sn concentrations up to 16.9% underwent here annealing at temperatures as high as 400 °C for 20 min without Sn segregation, in contrast with the full segregation observed in the corresponding blanket layers annealed simultaneously. After annealing, no changes in the elemental composition of the microdisks were evidenced. An enhancement of the total integrated photoluminescence, with no modifications of the emission energy, was also observed. These findings show that microstructuring offers a completely new path in maintaining the stability of high Sn concentration Ge_1-xSn_x layers at temperatures much higher than those used for growth. This approach enables the use of thermal annealing processes to improve the properties of this alloy in optoelectronic devices (such as light emitting diodes, lasers, photodetectors, or modulators). It should also facilitate the integration of Ge_1-xSn_x into well-established technologies requiring medium temperature processes. The same strategy may help to prevent Sn segregation during high temperature processes in similar metastable alloys.