Investigating the stability of molecule doped graphene field effect transistors

Molecular doping has been considered as one of the promising methods to modulate the electrical property of graphene due to its easy operation and no defect generation. However, its stability has not yet been studied. In this study, large area graphene films were synthesized by chemical vapor deposition. The graphene field effect transistors (GFETs) were fabricated by photolithography. The electrical transport measurement demonstrates that the Dirac point of GFETs shifts from +54 V to −22 V after doping the GFETs with a polyethylenimine (PEI) molecule. Further, the influence of the electrical annealing and exposure time to air were systemically studied. The results show that the PEI molecule could be removed under a large measurement current and the electron mobility decreased faster than that of hole mobility under electrical annealing. The study of the PEI doped GFETs exposed to air shows that the oxygen and water firstly interacts with the PEI molecule and then directly interacts with graphene. The electrical properties of PEI doped CVD-grown graphene transistors have been studied in detail, demonstrating that the absorbed PEI molecular will be modified by oxygen or water molecular during the exposure in ambient.