Fig. 3: Gate efficiency in the center of the channel and the contact region.
From: Contact spacing controls the on-current for all-carbon field effect transistors
The gate induced shift of the energy bands ξ in the channel center (solid blue line) and the contact region (dashed yellow line) as a function of the gate-source voltage VGS. Compared to metallic electrodes, the graphene electrodes cannot entirely screen the carbon nanotube (CNT) from the gate field, whereby the CNT can also be electrostatically doped in the contact region. We explain the almost linear behavior of the band shift in the channel center by the fact that the Fermi level lies within the bandgap of the CNT, where the quantum capacitance is zero. For slightly increased (decreased) gate-source voltages, the linear behavior is damped rapidly because the Fermi level reaches the first van Hove singularity (VHS).
