Introduction
Graphene is a zero-gap semiconductor. Therefore, graphene exhibits metallic conductivity, and the absence of a bandgap renders its applications in electronic devices (FETs and solar cell). Doping heteroatoms into graphene is a promising and feasible way to change its chemical composition, tailor its electronic band structure as well as modify the local chemical activity of graphene .
N-Doped graphene

A one-step method has been developed for the growth of large-area, continuous, uniform and single layered N-doped graphene on Cu foil via CVD technique. The sheets appear to be quite uniform with only a small fraction of multilayer (<3%). Most area of the films (>97%) is monolayer.
As shown in SEM image, the N-doped graphene sheet is continuous across the surface steps and grain boundaries of Cu. The produced wrinkles on the surface are associated with the thermal expansion coefficient differences between the substrate and N-doped graphene
 
N atoms were suggested to mainly form a “pyrrolic” nitrogen structure, and the doping level of N reached up to 3.4 at.%. The film is highly continuous and uniform. The measured thickness for N-doped graphene is ~0.91 nm, which is close to that reported for single layer graphene on SiO2.

The FETs in large scale were fabricated. The sheet resistance of N-doped graphene is in the range of 14-34 kΩ/o, and the mobilities are in about 310-630 cm2/Vs . Ids increases with increasing Vg, indicating an n-type semiconductor behavior.
S-Doped graphene
Large area, continuous and crumpled membrane was formed. the absorbance particles on the surface of graphene are sulfur aggregates.


The high D band indicates that graphene’s network is locally disturbed after introducing sulfur atoms into its lattice. The 2D peak could be fitted to a single peak, indicating the existence of monolayer .

The observation of edge determined that single layer predominately formed in S-doped graphene sheets. The SAED revealed a hexagonal pattern, which confirmed the three-fold symmetry of carbon atom arrangement. Sulfur atoms automatically arranged in the linear superlattice structure and acted as a bridge to connect sp2 carbon hexagonal lattice to form the superlattice network. The states of sulfur atoms were much similar to the neutral sulfur.

The typical sheet of pristine graphene’s resistivity was about 130 Ω/o. But for S-doped graphene, the Id-Vd curve exhibited semiconductor-like conducting behavior after sulfur doping. The resistivity reached to 6.28×103 Ω/o at the voltage of 1.5 V in S-doped graphene. The mobility of S-doped graphene was about 500-610 cm2 V-1 s-1 . After doping sulfur, the p-type semiconducting behavior has been greatly enhanced.
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