The influence of the edge effect of the mask on the strain and the morphology of SiGe film grown at the patterned Si substrate by molecular beam epitaxy

The influence of the edge effect of the mask on the strain and the morphology of the Si0.8Ge0.2 films grown at the patterned Si substrates with different mask materials were studied. Experiments showed that for the Si0.8Ge0.2 films grown in the micron size windows by molecular beam epitaxy, both the strain and the dislocation density would be less than that of the film grown at the large area of the same substrate, as the film thickness was over the critical thickness for pesudomorphic growth. This phenomenon did not conform with the common case that the strain of the heteroepitaxial film would reduce while the misfit dislocation occurred. Further studies on the strain at different regions of Si0.8Ge0.2 film in the window were made by micro Raman scattering spectrum measurement. The results showed that if the SiO2 film was used as the mask material, the strain of the Si0.8Ge0.2 film at the margin of the window was larger than that of the film at the central area. But the contrary case could be observed if the mask material of Si3N4 was used. Besides the obvious differences of the morphology of the Si0.8Ge0.2 films in the windows with different mask materials were observed by atomic force microscope measurements. We suggest that these results may be attributed to the edge effects of the mask and the epitaxial film.