Characterization of crystallinity of Ge1−xSnx epitaxial layers grown using metal-organic chemical vapor deposition

The epitaxial growth of a Ge1 − xSnx layer was examined using metal-organic chemical vapor deposition (MOCVD) with two types of Ge precursors; tetra-ethyl-germane (TEGe) and tertiary-butyl-germane (TBGe); and the Sn precursor tri-butyl-vinyl-tin (TBVSn). Though the growth of a Ge1 − xSnx layer on a Ge(001) substrate by MOCVD has been reported, a high-Sn-content Ge1 − xSnx layer and the exploration of MO material combinations for Ge1 − xSnx growth have not been reported. Therefore, the epitaxial growth of a Ge1 − xSnx layer on Ge(001) and Si(001) substrates was examined using these precursors. The Ge1 − xSnx layers were pseudomorphically grown on a Ge(001) substrate, while the Ge1 − xSnx layer with a high degree of strain relaxation was obtained on a Si(001) substrate. Additionally, it was found that the two Ge precursors have different growth temperature ranges, where the TBGe could realize a higher growth rate at a lower growth temperature than the TEGe. The Ge1 − xSnx layers grown using a combination of TBGe and TBVSn exhibited a higher crystalline quality and a smoother surface compared with the Ge1 − xSnx layer prepared by low-temperature molecular beam epitaxy. In this study, a Ge1 − xSnx epitaxial layer with a Sn content as high as 5.1% on a Ge(001) substrate was achieved by MOCVD at 300 °C.