Influence of Ge substrate orientation on crystalline structures of Ge1−xSnx epitaxial layers

We have investigated the substrate orientation dependence of the crystallinity and strain relaxation behavior of Ge and Ge1−xSnx layers epitaxially grown on Ge(001), (110), and (111) substrates. The strain relaxation in Ge1−xSnx layers on Ge(110) and (111) occurs from a strain value smaller than that on Ge(001). We obtained the critical strain energy of a Ge1−xSnx layer regardless of Ge substrate orientation. As a result, we achieved the epitaxial growth of pseudomorphic Ge1−xSnx layers with high substitutional Sn contents of 8.5% and 6.7% on Ge(110) and (111) substrates, respectively. •Pseudomorphic Ge1−xSnx (x>0.005) on Ge(110) and (111) has been achieved.•The critical energy of strain relaxation of Ge1−xSnx was observed regardless of orientation.•Flat surface of Ge1−xSnx layer with a high Sn content can be formed by decreasing the thickness.