Germanium-tin films with rather high Sn content (28.04％ and 29.61％) are deposited directly on Si (100) and Si (111) substrates by magnetron sputtering.The mechanism of the effect of rapid thermal annealing on the Sn surface segregation of Ge1-xSnx films is investigated by x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).The x-ray diffraction (XRD) is also performed to determine the crystallinities of the Ge1-xSnx films.The experimental results indicate that root mean square (RMS) values of the annealed samples are comparatively small and have no noticeable changes for the as-grown sample when annealing temperature is below 400 ℃.The diameter of the Sn three-dimensional (3D) island becomes larger than that of an as-grown sample when the annealing temperature is 700 ℃.In addition,the Sn surface composition decreases when annealing temperature ranges from 400 ℃ to 700 ℃.However,Sn bulk compositions in samples A and B are kept almost unchanged when the annealing temperature is below 600 ℃.The present investigation demonstrates that the crystallinity of Ge1-xSnx/Si (111) has no obvious advantage over that of Ge1-xSnx/Si (100) and the selection of Si (111) substrate is an effective method to improve the surface morphologies of Ge1-xSnx films.We also find that more severe Sn surface segregation occurs in the Ge1 xSnx/Si (111) sample during annealing than in the Ge1-xSnx/Si (100) sample.