The Low Frequency Noise Spectrum in Gated Epitaxial Graphene Field Effect Transistors

The low frequency noise (LFN) spectrum characteristics in ungated and gated ca. 1 ML graphene field effect transistor structures are presented. Synthesis was via the Ar ambient method in a commercial reactor on semi-insulating on-axis 6H(0001)SiC. Samples were processed using photolithography before dielectric deposition; Ti/Au stack was used for ohmic and gate contacts. High-κ dielectric deposition used F-functionalization followed by atomic layer deposition of 15 nm Al₂O₃ or HfO₂. The LFN data was averaged over 5 different samples on the same substrate for each oxide case. The LFN spectrum, proportional to 1/f, was similar in magnitude for both bare and dielectric covered graphene, implying the F-functionalization process does not appreciably add noise generation-recombination centers. Both gate oxides showed noise hysteresis (~15%) although it was more pronounced for the HfO₂ devices. The LFN increased with increasing carrier concentration but decreased with increasing mobility implying that the empirical Hooge model cannot explain the origin of the noise and points to carrier scattering mechanisms as the noise source.