We have investigated how to realize a strain-relaxed Ge1-xSnx layer with large in-plane lattice constant as a buffer layer for a tensile-strained Ge layer. This paper reports the dependence of strain relaxation behavior in Ge1-xSnx layers on the misfit strain at the interface between Ge1-xSx, layers and substrates. We examined control of the misfit strain by growth of Ge1-xSnx layers on bulk-Si and virtual Ge substrates. Large misfit strain between the Ge1-xSnx layer and the Si substrate leads to strain relaxation during growth and high degree of strain relaxation after annealing. However, it also leads to interfacial mixing and surface roughening with annealing. As a result, the Ge1-xSnx layer having a Sn content of 9.2% was achieved, and it has a potential to induce a tensile strain of 0.99% in Ge layer. (C) 2011 Elsevier Ltd. All rights reserved.