Reduction of hole doping of chemical vapor deposition grown graphene by photoresist selection and thermal treatment

The doping effect on graphene by photoresists were studied in this article. Polymethyl methacrylate (PMMA) is the usual choice for graphene transfer, but it is known to leave a significant amount of residue. PMMA results in strong hole doping and reduction of mobility of the graphene devices. Not only PMMA, but photoresists also leave residues during the lithographic steps and dope the graphene in strong hole-doping states along with water and oxygen molecules. In this article, we tested three types of photoresists for their effects on graphene's electrical properties. It was found that a specific photoresist can significantly reduce the amount of hole-doping of the graphene transistor more than other photoresists. The use of hydrophobic substrates and additional thermal treatment can help reducing the hole-doping further.