Further reduction of Schottky barrier height of Hf-germanide/n-Ge(001) contacts by forming epitaxial HfGe2

For realizing high-performance Ge-channel metal-oxide-semiconductor field-effect transistor (MOSFET), the reduction of parasitic resistance is one of the most important issues [1] . However, it is generally difficult to reduce the contact resistivity at metal/ n -Ge interface because of its high Schottky barrier height (SBH) around 0.5-0.6 eV, in which the Fermi level of the metal is pinned at the valence band edge of Ge; well-known Fermi level pinning (FLP) phenomenon [2] , [3] . One of the considerable reasons for FLP is disorder-induced gap states owing to dangling bonds at the metal/Ge interface [4] . There are some reports in which an epitaxial metal/Ge interface alleviates FLP and the SBH can be lowered with Fe 3 Si/ n -Ge(111) [5] , Mn 3 Ge 5 / n -Ge(111) [6] , and NiGe/ n -Ge(110) contacts [7] .