Characterization and thermal stability of GeSn/Ge multi-quantum wells on Ge (100) substrates

High-quality, high-Sn-content GeSn/Ge multi-quantum well (MQW) structures were grown on Ge (100) substrates by molecular beam epitaxy. The Sn content of the GeSn layers in the MQWs was 7.85 %. High crystalline quality and smooth interfaces were observed by high-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). Clear multistage satellite peaks were identifiable in the HRXRD results and were consistent with those obtained in simulations. No threading or misfit dislocations were observed in the TEM images. The room temperature photoluminescence showed an enhanced emission peak of direct transitions around 2025 nm due to the quantum confinement effect. Rapid thermal annealing was also performed and indicated that the MQW structures remained stable when annealed at 400 A degrees C for 30 s. With increasing temperature, the intermixing of the GeSn and Ge layers increased, and the structure completely degenerated at 600 A degrees C. These results will provide a valuable reference for the processing of GeSn devices.