Modulation of Fermi level pining position at metal/n-Ge interface by semimetal Ge1−xSnx and Sn interlayers

We have investigated the dependence on the metal work function of Schottky barrier height (SBH) of metal/Ge1−xSnx/n-Ge Schottky diode and have discussed the mechanism of SBH reduction by insertion of a Ge1−xSnx interlayer. The SBH of metal/Ge1−xSnx/n-Ge Schottky diodes for various metal electrodes of Zr, Al, and Au were estimated. Even after the insertion of Ge1−xSnx layer at various metal/n-Ge interface, the dependence of SBH on the metal work function is weak as well as direct metal/n-Ge contact. We also found that the SBH decreases by 0.1-0.2 eV by the insertion of a Ge1−xSnx or Sn layer regardless of the metal work function. This result means that the SBH is determined only by the interfacial semimetal Ge1−xSnx layer. Considering that density of states at the EF and momentum of electrons in semimetal Ge1−xSnx and α-Sn are small, those epitaxial interlayers would suppress the metal induced gap state at the metal/Ge interface as well as the disorder induced gap states. Additionally, we demonstrated the reduction of the metal/n-Ge contact resistivity by introduction of a Ge1−xSnx interlayer.