  The physical origin of Fermi level pinning (FLP) at metal/Ge interfaces has
been argued over a long period. Using the Fe$_{3}$Si/Ge(111) heterostructure
developed originally, we can explore electrical transport properties through
atomically matched metal/Ge junctions. Unlike the conventional metal/$p$-Ge
junctions reported so far, we clearly observe rectifying current-voltage
characteristics with a measurable Schottky barrier height, depending on the
contact area of the Fe$_{3}$Si/Ge(111) junction. These results indicate that
one should distinguish between intrinsic and extrinsic mechanisms for
discussing the formation of the Schottky barrier at metal/Ge interfaces. This
study will be developed for understanding FLP for almost all the
metal/semiconductor interfaces.
