Surface morphology of three kinds of Si(I I n) surfaces during Ga deposition has been studied by scanning tunneling microscopy to investigate nano-facet formation processes on high-index silicon surfaces. It has been observed that Si(l 13) surfaces with vicinal angles of +/-2degrees changed into nano-facet structures of (1 12) and (1 15) at I NIL Ga deposition as well as a flat Si(I 13). In contrast, no faceting occurred on Si(I 14). In all cases of nano-facet formation, (1 12) facet formed prior to (1 15) facet. Thus, it is considered that (1 12) facet formation is a driving force of nano-facet formation process. It is also considered that large angle difference between (1 1 2) and (1 14) prevents the facet formation on Si(l 14). Difference of vicinal direction appears in distribution of facet width. The facet width distribution strongly depends on the initial morphology on the surface tilted toward [3 3 (2) over bar] direction, while on the surface tilted toward [(3) over bar (3) over bar 2], initial morphology does not affect the final facet distribution. (C) 2003 Elsevier Science B.V. All rights reserved.