Surface roughening induced by a characteristic surface structure of a Si film grown on Si(1 1 1)

The changes in the surface morphology and the surface structure reconstruction on a Si film grown on Si(1 1 1) 7×7 superlattice held at Ts=250°C are observed with scanning tunneling microscopy and reflection high-energy electron diffraction. The surface morphology of the Si layer has begun to roughen immediately when the film thickness (d) is above 10 nm. The surface structure reconstruction on the growing Si film also changes with increased film thickness: at the initial growth stage (d<10 nm), the island showing the 5×5 dimer-adatom-stacking fault layer structure is predominantly formed, while atomic-row structures (c2×4 and 2×1) along the 〈1 1̄ 0〉 directions increase with the reduction of 5×5 islands in d>10 nm. The atomic-row structure will relate to the surface roughening, because the atomic-row structure increases with roughening of the surface. We also found a characteristic structure composed of the atomic-rows and propose a structure model which includes double twin boundaries underneath. The structure has a higher growth rate compared with that in the growth on the (1 1 1) surface.