Sub-micron size Schottky junctions on as-grown monolayer epitaxial graphene on Ge(100): a low-invasive scanned-probe based study

We report on the investigation of the Schottky barrier formed at the junction between a metal- free graphene monolayer and Ge semiconductor in the as-grown epitaxial graphene/Ge(100) system. In order to preserve the heterojunction properties, we defined sub-micron size graphene/Ge junctions using the scanning probe microscopy lithography in the local oxidation configuration, a low-invasive processing approach capable of inducing spatially controlled electrical separations among tiny graphene regions. Characteristic junction parameters were estimated from I-V curves collected using conductive-atomic force microscopy. The current-voltage characteristics showed a p-type Schottky contact behaviour, ascribed to the n-type to p-type conversion of the entire Ge substrate due to formation of a large density of acceptor defects during the graphene growth process. We estimated, for the first time, the energy barrier height in the as-grown graphene/Ge Schottky junction (φB~0.45 eV) indicating a n-type doping of the graphene layer with a Fermi level ~0.15 eV above the Dirac point. The Schottky barrier devices showed ideality factor values around 1.5 pointing to a high quality of the heterojunctions.