Bandgap Opening of Bilayer Graphene by Dual Doping from Organic Molecule and Substrate

The lack of a bandgap limits the application of pristine graphene in logic circuits and photonic devices. Breaking the inversion symmetry in bilayer graphene (BG) by charge transfer doping is a promising way to open a bandgap. In this work, a sizable bandgap is created in BG by the opposite doping from organic molecule and substrate. Our first-principles calculations have quantitatively identified that BG is n-doped in the N,N-dimethyl-p-phenylenediamine/BG (DMPD/BG) system while it is p-doped in the tetracyanoethylene/BG (TCNE/BG) system. The opposite p-doping from amorphous SiO2 substrate with O-2(-) on its surface (a-SiO2-p) increases the bandgap of DMPD/BG from 106 to 253 meV. Similarly, the bandgap of TCNE/BG is enhanced from 98 to 211 meV by the opposite n-doping from Si-terminated 4H-SiC(0001) with a C buffer layer (C-SiC-n). Moreover, the molecular level of DMPD and a-SiO2-p related states locate below the opened bandgap, while the molecular levels of TCNE and C-SiC-n induced states lie above the bandgap. The increased bandgap without the intergap states should really improve the on/off current ratio of BG-based electronic devices. Meanwhile, the high carrier mobility is largely maintained due to the weak interaction at the interface. Thus, this work provides the scientific basis for further development in BG-based electronic devices.