Low-energy electron-irradiation effect on transport properties of graphene field effect transistors

The use of scanning electron microscopy (SEM), transmission electron microscopy (TEM) as well as electron beam lithography (EBL) and focus ion beam (FIB) processing in ultra-high vacuum represents a necessary step for the fabrication and characterization of graphene based devices. Consequently, graphene devices during fabrication or under test are necessarily exposed to high vacuum and electron irradiation that may considerably affect their electronic properties. We study the effects of low-energy electron beam irradiation up to 10 keV on graphene based field effect transistors. We fabricate metallic bilayer electrodes to contact mono- and bi-layer graphene flakes on SiO2, obtaining specific contact resistivity ≈ 19 Ω and carrier mobility as high as 4000 cm2V-1s-1. By using a highly doped p-Si/SiO2 substrate as back gate, we analyze the transport properties of the device and the dependence on the pressure and on the electron bombardment. We demonstrate that low energy irradiation is detrimental on the transistor current capability, resulting in an increase of the contact resistance and a reduction of the carrier mobility even at electron doses as low as 30 e-/nm2. We also show that the irradiated devices recover by returning to their pristine state after few repeated electrical measurements.