A Significant Shift of Schottky Barrier Heights at Strongly Pinned Metal/Germanium Interface by Inserting an Ultra-Thin Insulating Film

At any metal/germanium (Ge) interfaces, Schottky junctions to n-Ge and ohmic ones to p-Ge are formed by the strong Fermi level pinning to the valence band edge of Ge. In this paper, we report that Schottky-ohmic characteristics are reversed by inserting an ultra-thin oxide film into the metal/Ge interface. A gradual change of Schottky barrier heights (SBHs) with increasing insulating film thickness has been found, which supports that the origin of Fermi level pinning at the metal/Ge junction is caused by the metal-induced gap states. Furthermore, the SBH change enables us to operate metal source/drain Ge n-channel metal–oxide–semiconductor field effect transistors (n-MOSFETs) without any impurity doping. We demonstrate the metal source/drain Ge n-MOSFET with a peak mobility of 270 cm2/(V·s).