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.