We have investigated the influence of tensile and compressive strain on the crystalline structures of Ge1-x-ySixSny epitaxial layers. The tensile strain in Ge1-x-ySixSny induces a non-uniform crystallinity of (220) lattice planes and surface roughening despite the strain magnitude is as small as 0.20%. In contrast, the unstrained or compressive strained Ge1-x-ySixSny layer exhibits a flat and uniform surface and high crystallinity. We found that the control of the sign of the strain is an important factor to obtain a high quality Ge1-x-ySixSny layer. Furthermore, substitutional Sn atoms in Ge1-x-ySixSny epitaxial layer with an Sn content of 10% are thermally stable for annealing at 500 degrees C. (C) 2015 Elsevier Ltd. All rights reserved.