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

We have investigated the substrate orientation dependence of the crystallinity and strain relaxation behavior of Ge and Ge 1 − x Sn x layers epitaxially grown on Ge(001), (110), and (111) substrates. The strain relaxation in Ge 1 − x Sn x 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 Ge 1 − x Sn x layer regardless of Ge substrate orientation. As a result, we achieved the epitaxial growth of pseudomorphic Ge 1 − x Sn x layers with high substitutional Sn contents of 8.5% and 6.7% on Ge(110) and (111) substrates, respectively.