  We directly image hot spot formation in functioning mono- and bilayer
graphene field effect transistors (GFETs) using infrared thermal microscopy.
Correlating with an electrical-thermal transport model provides insight into
carrier distributions, fields, and GFET power dissipation. The hot spot
corresponds to the location of minimum charge density along the GFET; by
changing the applied bias this can be shifted between electrodes or held in the
middle of the channel in ambipolar transport. Interestingly, the hot spot shape
bears the imprint of the density of states in mono- vs. bilayer graphene. More
broadly, we find that thermal imaging combined with self-consistent simulation
provides a non-invasive approach for more deeply examining transport and energy
dissipation in nanoscale devices.
