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 cm2 V−1 s−1. The work function and its uniformity on a large scale (1.2 mm × 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. The doping effect of solution‐processed N‐DMBI molecules on CVD‐grown graphene is investigated. The strong n‐type doping shifts the Dirac point of graphene to around ‐140 V. A electron mobility of 1150 cm2 V−1 s−1 is obtained. The doping effect is uniform on a large scale and stable in the air.