De-doping of graphene by Joule heating with water

We report the restoration of electrical properties found in graphene field-effect transistors (G-FETs) Joule heated with water. Since polymer contaminates the graphene surface during the transfer process and device fabrication, the graphene becomes p-doped so that we can hardly measure its charge neutrality point (CNP) with a gate voltage even up to 100 V. When the p-doped G-FET covered by water is Joule heated, on the other hand, the CNP is restored almost to the zero gate voltage. Based on the results derived from I _d-V _g characteristics and Raman spectroscopy, we argue that the polymers on graphene were removed whilst it was Joule heated, resulting in high de-doping of the graphene, leading to the easy process for the fabrication of high performance G-FET.