Metal-induced nanocrystalline structures in Ni-containing amorphous silicon thin films

摘要

The mechanisms of silicon nanocrystal structure formation in amorphous Si films have been studied for a relative Ni impurity content varying between 0.1 and 10 at. %, i.e., from a Ni doping range to the Si-Ni alloy phase. The films, deposited by the cosputtering technique at 200℃, were submitted to isochronal (15 min) annealing cycles up to 800℃. Four different substrates were used to deposit the studied films: crystalline (c-) quartz, c-Si, c-Ge, and glass. Both the two orders of magnitude impurity concentration range variation and the very short annealing times were selected on purpose to investigate the first steps of the mechanism leading to the appearance of crystal seeds. The conclusions of this work are the following: (a) Ni impurity induces the low-temperature crystallization of amorphous silicon; (b) the NiSi_2 silicide phase mediates, at the surface or in the bulk of the film, the crystallization process; and (c) the onset of crystallization and the crystalline fraction of the samples at each temperature depend not only on the Ni impurity concentration, but also on the nature of the substrate.