Invited Paper GR+TF-TuA1
Graphene and Its Progeny: from Fundamental Material Properties to Device Applications

Tuesday, October 19, 2010, 2:00 pm, Room Brazos

The incredible material properties of graphene have spurred intense interest among chemists, physicists and engineers towards potentially exciting electronic applications. Much like nanotubes, graphene electrons have high mobilities due to the sharp curvature of their bands at the Gamma point that reduces their effective masses, as well as long scattering lengths due to symmetry selection rules among their pseudospin separated bands. However, a potential problem with graphene is its metallicity, which makes its ON-OFF ratio unacceptable for digital logic. Effort is under way to mitigate this by opening bandgaps through various chemical and electrostatic means. I will argue that any such band-gap opening leads to an inevitable reduction in mobility even if we manage to do so without affecting its scattering length. The trade-off arises from a fundamental asymptotic constraint on all graphitic materials (epitaxial graphene, strained graphene, nanoribbons, nanotubes, and bilayer graphene) that pins the high energy electrons away from the Gamma point to an ultimately linear dispersion. However, opening a bandgap by width confinement, e.g. in a nanoribbons, can provide distinct electrostatic if not material advantages. The presence of diffuse boundary conditions at the edges, along with strain and edge roughness, systematically erases any signs of chirality and metallicity in GNRs, making their widths the single arbiter of metallicity. This allows us to envisage wide-narrow-wide (WNW) nanoribbons monolithically patterned out of a single template into both switches and interconnects. The 2-D electrostatics of the source-drain contact edge capacitances improves the gate control, allowing the current to show a highly desirable saturation characteristic. Furthermore, the presence of C-C bonds at the channel-contact interface makes metal induced gap states relatively ineffective in pinning the bands, promoting Ohmic behavior. I will quantify the advantages and disadvantages of WNW devices, and compare with alternate GNR switches, such as utilizing electron focusing in p-n junctions.