N-Doped Graphene Field-Effect Transistors with Enhanced Electron Mobility and Air-Stability

Although graphene can be easily p-doped by various adsorbates, developing stable n-doped graphene that is very useful for practical device applications is a difficult challenge. We investigated the doping effect of solution-processed (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI) on chemical-vapor-deposited (CVD) graphene. Strong n-type doping is confirmed by Raman spectroscopy and the electrical transport characteristics of graphene field-effect transistors. The strong n-type doping effect shifts the Dirac point to around -140 V. Appropriate annealing at a low temperature of 80 oC enables an enhanced electron mobility of 1150 cm(2) V-1 s(-1). The work function and its uniformity on a large scale (1.2 mm x 1.2 mm) of the doped surface are evaluated using ultraviolet photoelectron spectroscopy and Kelvin probe mapping. Stable electrical properties are observed in a device aged in air for more than one month.