Recent Progress of Graphene Doping

Doping is the most feasible and convenient method to modulate the band structure of graphene from semimetal to p-type or n-type material. In recent years, the chemical vapor deposition methods have been well developed to grow graphene layer with high quality and large area. This paper briefly reviews the recent research progress on doping methods of CVD graphene, including the doping effects by metals, small molecules, chemical reactions and replacement of lattice atoms. The methods of bilayer graphene band regulation as well as the fabrication of graphene p-n junction are also introduced, and the future tendency and potential applications of doped graphene are proposed. For graphene, it is relatively easy to produce p-type doping via surface absorption, exposing pristine graphene in those molecules with electron withdrawing groups (H2O, O-2, N-2, NO2, PMMA et al.) will lead to evident p-type doping, and graphene of this kind of p-type doping can rapidly recover to its original state when doping molecules are removed. If boron source was introduced into the CVD growth process of graphene, substitutional p-doping that some carbon atoms in graphene hexagonal lattice are replaced by boron atoms can be formed. Compared to the p-type doping, stable n-type doping is not facile for graphene. It has been proved that some electron-donating molecules such as ammonia, potassium, phosphorus, hydrogen and poly(ethyleneimine) (PEI) can produce n-type doping in graphene through surface electron transfer, but these doping effects are unstable. By introducing nitrogen-containing precursors in growth approach, small part of lattice carbon atoms will be replaced by nitrogen atoms which can result in effectively n-doping effect. Combine the p-type and n-type doping method together, the p-n junction can be produced in mono- or bi-layer graphene, a series of novel functional devices like photothermoelectric devices have been constructed using these hetero-doped graphene p-n junctions.