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Controlling Carriers in Graphene

Monday, October 18, 2010, 8:20 am, Room Brazos

Session: Epitaxial Graphene on SiC
Presenter: G.G. Jernigan, Naval Research Laboratory
Authors: G.G. Jernigan, Naval Research Laboratory
P.E. Thompson, Naval Research Laboratory
C.S. Hellberg, Naval Research Laboratory
J.L. Tedesco, Naval Research Laboratory
V.D. Wheeler, Naval Research Laboratory
L.O. Nyakiti, Naval Research Laboratory
P.M. Campbell, Naval Research Laboratory
D.K. Gaskill, Naval Research Laboratory
Correspondent: Click to Email
No technique for graphene synthesis yields controllably doped material. Measurements of carrier density and carrier type produce results that are dependent on extrinsic factors. For example, exfoliated graphene and metal-catalyzed graphene on SiO2 often obtain carriers through unwanted charges in the oxide[1] or by gas adsorption[2] making graphene p-type. Similarly, epitaxial graphene on SiC should be n-type due to work function differences with the underlying SiC substrate[3]. Our recent measurements of graphene grown on Si-face SiC show that device processing steps can cause it to switch between carrier types. Additionally, we have found graphene grown on C-face SiC to be highly doped by Si impurities, which can produce either electrons or holes.

We have begun a series of investigations to impart properties after growth on epitaxial graphene formed on Si- and C-face SiC[4-5]. Substitutional incorporation of impurity atoms can lead to doping in a graphene sheet, if their concentration does not drastically affect the pi-network. This can be achieved by selective oxidation to remove C atoms from the graphene lattice and by molecular beam deposition (MBE) of dopants with controllable ultra-low fluxes to fill the C vacancies. It is important to note that Group III and V dopants can maintain the 2D geometry of the graphene sheet without producing an unsaturated bond (as they do when incorporated into the bulk of Si.) Thus, the extra p-orbital electrons from the Group V elements can be added to the graphene pi-network, or Group III elements can provide extra holes, without adversely affecting carrier mobility. Using MBE, we have substitutionally doped graphene with B and P. Ultraviolet photoelectron spectroscopy (UPS) is used to observe shifts in the Fermi level resulting from doping, and we have seen up to a 110 meV shift with 1% B in the lattice of graphene. Discussion of scanning tunneling microscopy (STM) observations of dopant placement and electrical properties will be presented. Density functional theory has been used to compute the density of states for the doped system in support of the STM and electrical measurements.

[1] S. S. Datta, D. R. Strachan, E. J. Mele, and A.T.C. Johnson, Nano Lett. 9 (2009) 7.

[2] Y. Dan, Y. Lu, N.J. Kybert, Z. Luo and A.T.C. Johnson, Nano Lett., 9 (2009) 1472.

[3] T. Filleter, K. V. Emtsev, Th. Seyller, and R. Bennewitz, Appl. Phys. Lett. 93 (2008) 133117.

[4] G.G. Jernigan, et al., Nano Lett. 9, 2605 (2009).

[5] J.L. Tedesco, B.L. VanMil, R.L. Myers-Ward, J.M. McCrate, S.A. Kitt, P.M. Campbell, G.G. Jernigan, J.C. Culbertson, C.R. Eddy, Jr., and D.K. Gaskill, Appl. Phys. Lett., 95, 122102 (2009).