Thermal Stability of Ge/GeSn Nanostructures Grown by MBE on (001) Si/Ge Virtual Wafers

A stack of five metastable 200-nm-thick elastically strained GeSn epitaxial layers separated by 20-nm-thick Ge spacers was grown on (001) Si/Ge virtual substrate by MBE. The molar fraction of Sn in different layers varied from 0.005 to 0.10, increasing with the layer distance from the Ge buffer. The phase separation of the GeSn alloy during postgrowth annealing takes place along with plastic relaxation. The phase separation begins well before the completion of the plastic relaxation process. The degree of phase separation at a given annealing temperature depends strongly on the Sn content in the GeSn alloy. The Sn released from the decomposed GeSn alloy predominantly accumulates as an amorphous layer on the surface of the sample.