▎ 摘　　要

We report that the Dirac voltage of graphene field effect transistors (FETs) can be tuned by controlling the composition of hafnium lanthanum oxide (HfLaO) gate dielectrics. As the lanthanum percentage is increased in the HfLaO film, the charge neutrality point of the graphene FET is gradually shifted in the negative direction. The origin of this tuning is attributed to the hygroscopic nature of the lanthanum oxide, as it is found that lanthanum oxide in the HfLaO film absorbs water molecules below the graphene channel, resulting in the suppression of the p-doping in graphene. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3659691]