Scanning tunneling microscopy study of solid-phase epitaxy processes of amorphous silicon layers on silicon substrates

We investigate the solid-phase epitaxy (SPE) processes of amorphous layers on Si(001) prepared by vacuum evaporation, Ar+ sputtering and P+-ion implantation techniques, using a scanning tunneling microscope (STM). The as-prepared surfaces by vacuum evaporation and Ar+ sputtering show similar morphology being covered with homogeneous circular particles. In contrast, the surface morphology by ion implantation is gross roughened consisting of irregular hillocks. The evolution of the surface morphology by thermal annealing is strongly dependent on the preparation methods and the extent of the surface damage. On the deposited specimen, an anisotropic island growth is observed during annealing at 250–300°C. On the Ar+-ion bombarded surface, the particles coalesce upon thermal annealing at 245°C. Prolonged annealing at this temperature promotes crystallization of the amorphous layers. In contrast, rather high-temperature annealing at 730–950°C is needed to crystallize the P+-ion implanted surface. Even at this temperature, the surface contains voids, presumably due to structural depression or impurity segregation.