Determination of graphene work function and graphene-insulator-semiconductor band alignment by internal photoemission spectroscopy

We determined the band alignment of a graphene-insulator-semiconductor structure using internal photoemission spectroscopy. From the flatband voltage and Dirac voltage, we infer a $4.6× 1011cm−2$ negative extrinsic charge present on the graphene surface. Also, we extract the graphene work function to be 4.56 eV, in excellent agreement with theoretical and experimental values in literature. Electron and hole injection from heavily doped p-type silicon (Si) are both observed. The barrier height from the top of the valence band of Si to the bottom of the conduction band of silicon dioxide (SiO₂) is found to be 4.3 eV. The small optical absorption in graphene makes it a good transparent contact to enable the direct observation of hole injection from Si to graphene. The barrier height for holes escaping from the bottom of Si conduction band to the top of SiO₂ valence band is found to be 4.6 eV.