We investigated the crystalline structures of Ge1-xSnx heteroepitaxial layers with Sn contents greater than 20% grown on InP and Ge substrates. Considering the lattice mismatch between the Ge1-xSnx layers and the substrates, we achieved epitaxial growth of Ge1-xSnx layers with very high Sn content by suppressing the Sn precipitation; in addition, we improved upon the crystalline quality of Ge1-xSnx heteroepitaxial layers. As a result, we could successfully form a 130 nm-thick Ge1-xSnx heteroepitaxial layer on an InP substrate with a Sn content as high as 27% without Sn precipitation. We also improved the crystalline quality of Ge1-xSnx layers by annealing at a temperature as low as 290 degrees C. (C) 2011 Elsevier B.V. All rights reserved.