Reduced Contact Resistance Between Metal and n-Ge by Insertion of ZnO with Argon Plasma Treatment.

We investigate the metal-insulator-semiconductor contacts on n-Ge utilizing a ZnO interfacial layer (IL) to overcome the Fermi-level pinning (FLP) effect at metal/Ge interface and reduce the barrier height for electrons. A small conduction band offset of 0.22 eV at the interface between ZnO and n-Ge is obtained, and the ZnO IL leads to the significant reduced contact resistance (R) in metal/ZnO/n-Ge compared to the control device without ZnO, due to the elimination of FLP. It is observed that the argon (Ar) plasma treatment of ZnO can further improve the R characteristics in Al/ZnO/n-Ge device, which is due to that Ar plasma treatment increases the concentration of oxygen vacancy V, acting as n-type dopants in ZnO. The ohmic contact is demonstrated in the Al/ZnO/n-Ge with a dopant concentration of 3 × 10 cm in Ge. On the heavily doped n-Ge with a phosphor ion (P) implantation, a specific contact resistivity of 2.86 × 10 Ω cm is achieved in Al/ZnO/n-Ge with Ar plasma treatment.