Fermi-level depinning of Ge surface using hydrogen plasma-immersion ion implantation

Hydrogen plasma immersion ion implantation (PIII) has been demonstrated for alleviating Fermi-level pinning in Al/Ge junctions. The Al metal contacts with n- and p-type Ge without hydrogen PIII treatment displayed Schottky and ohmic behavior despite their low metal work functions, which can usually be ascribed to the strong Fermi-level pinning mechanism. The Al contact to the hydrogen PIII treated n- and p-type Ge, however, displayed ohmic and Schottky behavior having barrier heights of 0.01 and 0.41 eV, respectively. This signifies Fermi-level unpinning in Al/Ge junctions. Hydrogen PIII treatment of Ge led to the creation of a 3-nm-thick amorphous Ge (a-Ge) layer at the surface, followed by a 9-nm-thick damaged layer. Annealing the PIII-treated Al/Ge contact at 800 °C resulted in a current level similar to that of the untreated contact. This could be ascribed to the recovery of PIII-induced surface damage through recrystallization of the α−Ge layer. The results of this study provide an approach for effective Fermi-level unpinning in metal/Ge junctions, which could be advantageous for the design of Ge-based devices with improved performance.