Work

Contact doping, Klein tunneling, and asymmetry of shot noise in suspended graphene

Year: 2016

Type: article

Abstract: The inherent asymmetry of the electric transport in graphene is attributed to Klein tunneling across barriers defined by $pn$ interfaces between positively and negatively charged regions. By combining conductance and shot noise experiments, we determine the main characteristics of the tunneling barrier (height and slope) in a high-quality suspended sample with Au/Cr/Au contacts. We observe an asymmetric resistance ${R}_{\mathrm{odd}}=100\ensuremath{-}70\phantom{\rule{4pt}{0ex}}\mathrm{\ensuremath{\Omega}}$ across the Dirac point of the suspended graphene at carrier density $|{n}_{\mathrm{G}}|=(0.3\ensuremath{-}4)\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$, while the Fano factor displays a nonmonotonic asymmetry in the range ${F}_{\mathrm{odd}}\ensuremath{\sim}0.03$--0.1. Our findings agree with analytical calculations based on the Dirac equation with a trapezoidal barrier. Comparison between the model and the data yields the barrier height for tunneling, an estimate of the thickness of the $pn$ interface $d<20$ nm, and the contact region doping corresponding to a Fermi level offset of $\ensuremath{\sim}\ensuremath{-}18$ meV. The strength of pinning of the Fermi level under the metallic contact is characterized in terms of the contact capacitance ${C}_{c}=19\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6} \text{F}/{\mathrm{cm}}^{2}$. Additionally, we show that the gate voltage corresponding to the Dirac point is given by the difference in work functions between the backgate material and graphene.

Source: Physical review. B./Physical review. B

DOI: 10.1103/physrevb.93.115413