Probing carrier concentration in gated single layer, bilayer and trilayer CVD graphene using Raman Spectroscopy

In this study, we experimentally investigate the evolution of the Raman spectrum of single, bi- and tri-layer graphene as function of gate voltage induced doping. In single layer graphene, the observed results are in agreement with the literature. Whereas, for bi- and tri-layer graphene, we report new results on the gate voltage induced doping dependence of G and 2D bands position, the 2D to G band intensity ratio and the G band linewidth. The gate bias through 90 nm-thick oxide allows us to move the Fermi level up to 0.43 eV and 0.31 eV for bi- and tri-layer graphene, respectively. We observe one minima in the evolution of the G band position of bilayer as function of doping. This result is explained by the presence of a larger charge density non-uniformity, which yields to electron and hole puddles in the sample. The G band position and linewidth and the 2D to G band intensity ratio show a slow variation with doping near the neutrality point, this becomes more important as doping keeps rising such as the trends present a parabolic shape dependence. We assign this to the band structure of bi- and tri-layer graphene where the carriers are massive with respect to single layer graphene