Fermi-Level Depinning of Ge Schottky Junction Using Se Treatment

Depinning of the Fermi-level at metal/Ge Schottky junctions was achieved by Se treatment at room temperature. Due to the strong Fermi-level pinning close to the valence band edge in Ge, Schottky and Ohmic behaviors were observed in conventional Al Schottky contacts to n- and p-type Ge, respectively. However, Al Schottky contacts to n- and p-type Ge with Se treatment became Ohmic and Schottky, respectively. Electron and hole barrier heights calculated using Richardson plots were found to be 0.15 eV for of Al contacts to Se-treated n- type Ge, and 0.33 eV for Al contacts to Se-treated p-type Ge, respectively. The transmission electron microscopy (TEM) examination combined with X-ray photoemission spectroscopy (XPS) analysis showed that Se treatment at room temperature yielded the formation of a fairly uniform Se-Ge alloy film with partially ionic binding nature caused by the chemical reaction between Se and Ge. This led to the reduction of surface states of Ge surface along with the passivation of dangling bonds by the incorporation of Se atoms, which was responsible for Fermi-level depinning at Al/Ge junctions.