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 Ge_(1-x)Sn_x 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 Ge_(1-x)Sn_x 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(3 D) 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 Ge_(1-x)Sn_x/Si(111) has no obvious advantage over that of Ge_(1-x)Sn_x/Si(100) and the selection of Si(111) substrate is an effective method to improve the surface morphologies of Ge_(1-x)Sn_x films. We also find that more severe Sn surface segregation occurs in the Ge_(1-x)Sn_x/Si(111) sample during annealing than in the Ge_(1-x)Sn_x/Si(100) sample. 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 Ge_ (1-x) Sn_x 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 crystallites of the Ge_ (1-x) Sn_x 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 ° C. The diameter of the Sn three-dimensional (3 D) island becomes larger than that of an as-grown sample when the annealing temperature is 700 ° C. In addition, the Sn surface composition decreases when the annealing temperature ranges from 400 ° C. to 700 ° C. However, Sn bulk compositions in samples A and B are kept almost unchanged when the a The present investigation reveals that the crystallinity of Ge_ (1-x) Sn_x / Si (111) has no obvious advantage over that of Ge_ (1-x) Sn_x / Si Si (111) substrate is an effective method to improve the surface morphologies of Ge_ (1-x) Sn_x films. We also find that more severe Sn surface segregation occurs in the Ge_ (1-x) Sn_x / Si annealing than in the Ge_ (1-x) Sn_x / Si (100) sample.