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 Fermilevel 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 degrees 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 alpha-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.