Chemically induced Fermi level pinning effects of high-k dielectrics on graphene.

High-k materials such as AlO and HfO are widely used as gate dielectrics in graphene devices. However, the effective work function values of metal gate in graphene FET are significantly deviated from their vacuum work function, which is similar to the Fermi level pinning effect observed in silicon MOSFETs with high-k dielectric. The degree of deviation represented by a pinning factor was much worse with HfO (pinning factor (S) = 0.19) than with AlO (S = 0.69). We propose that the significant pinning-like behaviors induced by HfO are correlated with the oxygen exchange reactions occurred at the interface of graphene and HfO.