Atomic force microscopy (AFM) has been employed to observe the top surface morphology of hydrogenated amorphous silicon-germanium alloys at the initial stage of deposition. It shows that the different growth mode is dominant for a sample with low and high germanium content, which strongly influences the structures and the photoelectric properties of the corresponding bulk films. The samples with hydrogen plasma annealing are also investigated by AFM in order to understand the effect of hydrogen annealing on the structure of a-SiGe:H films.