Effects of period number and sputtering time on optical properties of Si/Ge multilayer films deposited by magnetron sputtering

Si/Ge multilayer films were deposited by radio frequency magnetron sputtering method, and effects of period number and sputtering time on structure and optical absorption properties of the films were investigated by XP-1 profilometer, XRD, SEM, AFM, Ramman and UV–Vis techniques. Results indicated that the films exhibited the incomplete crystallization, and the appropriate period number benefited the ordering of the Si. Simultaneously, the films showed smooth growth, and the islands were spread all over the surface, and changing of the roughness was attributed to the interface effects. Strong absorption range in the UV–Vis spectra was enlarged with increasing period numbers, and there was a general trend for the band gaps to decrease with increasing period numbers, accompanied the gradually decreasing amplitude. Theoretical calculation and analysis displayed that the ECB value gradually increased and the EVB value gradually decreased with the increasing period number, eventually resulting in the decreasing band gap, and the corresponding values remained stable at different sputtering time when period number was 5.