Intrinsic Dirac Point Energy Level and Band Offset of Graphene/SiO$_2$ interface

Advancing toward the rational design, fabrication, and implementation of graphene(GR)-based electronic and optical devices, the intrinsic barrier height of undoped GR (the Dirac point of GR to the conduction band(CB) edge of an insulator), as well as the intrinsic work function(WF) of GR must be accurately determined. We present an internal photoemission (IPE) investigation of a unique semi-transparent metal/high-k/GR/SiO$_{2}$/Si structure, and focus our study on the photoemission phenomena at the GR/SiO$_{2}$ interface. By taking advantage of the optical interference of the SiO$_2$ cavity, the enhanced photoemission from GR was observed. As a result, a complete electronic band alignment at the GR/SiO$_{2}$/Si interfaces is established. The intrinsic positions of the undoped GR Dirac point with respect to the CB of SiO$_2$, 3.58 eV (Al$_2$O$_3$ TG) and 3.60 eV (HfO$_2$ TG), are obtained. The intrinsic WF of graphene is found to be 4.50 eV. The determination of the WF of GR is of significant importance to the engineering of GR-base devices and the IPE spectroscopy, combined with specific interference cavity structures, would be a valuable measurement technique for other GR-like2-D material systems.