Direct Measurement of Intrinsic Dirac Point and Fermi level at Graphene/Oxide interface and Its Band Alignment by Cavity Enhanced Internal Photoemission
Kun Xu, Caifu Zeng, Qin Zhang, Rusen Yan, Peide Ye, Kang Wang, Alan C. Seabaugh, Huili G. Xing, John S. Suehle, Curt A. Richter, David J. Gundlach, Nhan V. Nguyen
We report the first direct measurement of the Dirac point, the Fermi level, and the work function of graphene by performing internal photoemission measurements on a graphene/SiO2/Si structure with a unique optical-cavity enhanced test structure. A complete electronic band alignment at the graphene/SiO2/Si interfaces is accurately constructed. The observation of enhanced photoemission from a one-atom thick graphene layer was possible by taking advantage of the optical interference in the SiO2 cavity. The photoemission yield was found to follow the well-known linear density-of- states dispersion in the vicinity of the Dirac point. At the flat band condition, the Fermi level was extracted and found to reside 3.3 eV below the bottom of SiO2 conduction band. When combined with the shift of the Fermi level from the Dirac point we are able to unambiguously ascertain the position of the Dirac point at 3.6 eV with respect to the bottom of the SiO2 conduction band; yielding a work function of 4.5 eV which is in an excellent agreement with theory.