Graphene for metal-semiconductor Ohmic contacts

One of the key components of modern device structures is the metal-semiconductor (MS) contact with low symmetric contact resistance. We report on a MS contact structure utilizing graphene insertion. In this strategy, graphene reduces or even eliminates in ideal conditions, the Fermi-level pinning at a MS junction. Since the metal, Ni, deposited on graphene reduced the work function of graphene, the doped graphene was able to lower the Schottky barrier at the MS junction. The Schottky barrier height of metal-graphene-Si (MGS) junction was obtained from temperature dependent I-V characteristics. We confirmed that the graphene doped with Ni reduced the Schottky barrier height from 0.67 eV to 0.20 eV in wafer scale test. We also demonstrated the formation of an ideal MGS Ohmic contact via conductive atomic force microscopy. The contact resistance of the ideal MGS was less than 1.0×10^-6 Ω cm² with low doped Si (10¹⁵ cm³). The resistance is comparable to that of a current device contact with highly doped Si. Since it only requires the insertion of a single layer of graphene, this method can be directly applied to the current Si technology to reduce the contact resistance at MS junctions.