n-Type Behavior of Graphene Supported on Si/SiO2 Substrates

ORAL

Abstract

Results are presented from an experimental and theoretical study of electronic properties of back-gated graphene field effect transistors (FETs) on Si/SiO$_{2}$ substrates. The excess charge on the graphene was observed by sweeping the gate voltage to determine the charge neutrality point in the graphene. Devices exposed to laboratory environment for several days were always found to be initially p-type. After $\sim $20 h at 200 \r{ }C in $\sim $5$\times $10$^{-7}$ Torr vacuum, the FET slowly evolved to n-type behavior with a final excess electron density on the graphene of 4$\times $10$^{12}$ electrons/cm$^{2}$. This value is in excellent agreement with our theoretical calculations on SiO$_{2}$, where we have used molecular dynamics to build the SiO$_{2}$ structure and then density functional theory to compute the electronic structure. The essential theoretical result is that SiO$_{2}$ has a significant surface state density just below the conduction band edge that donates electrons to the graphene to balance the chemical potential at the interface. An electrostatic model for the FET is also presented that produces an expression for the gate bias dependence of the carrier density.

*This work is supported by NSF NIRT ECS 06-09243.

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Authors

  • Humberto Gutierrez

    • Department of Physics, The Pennsylvania State University
    • Physics Department, Pennsylvania State University
    • Department of Physics, Pennsylvania State University
    • Physics Department, Penn State University

  • Hugo Romero

    • Dept. of Physics, Penn State
    • Physics Department, Pennsylvania State University
    • Physics Department, Penn State University

  • Ning Sheng

    • Physics Department, Penn State University

  • Jorge Sofo

    • Department of Physics, The Pennsylvania State University
    • Physics Department, Penn State University

  • Peter Eklund

    • Physics Department, Penn State University
    • Dept. of Physics, Penn State
    • Department of Physics, The Pennsylvania State University
    • Department of Physics, Department of Materials Science and Engeering, The Pennsylvania State University
    • Department of Physics, Department of Material Science and Engineering, Pennsylvania State University, University Park, PA 16802
    • Physics Department, Material Science \& Engineering Department
    • Department of Physics, Department of Material Sciece and Engineering, Pennsylvania State University
    • Department of Physics, Department of Materials Science \& Engineering and Materials Research Institute, Penn State University
    • Physics Department,Materials Science \& Engineering Department, Pennsylvania State University

  • Parsoon Joshi

    • Electrical Engineering Department, Pennsylvania State University
    • Electrical Engineering Department, Penn State University

  • Srinivas Tadigadapa

    • Electrical Engineering Department, Pennsylvania State University
    • Electrical Engineering Department, Penn State University