Doping of adsorbed graphene from defects and impurities in SiO${}_{2}$ substrates

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Doping of adsorbed graphene from defects and impurities in SiO $_{2}$ substrates

Razvan A. Nistor, Marcelo A. Kuroda, Ahmed A. Maarouf, and Glenn J. Martyna

Phys. Rev. B 86, 041409(R) – Published 27 July 2012

Abstract

The performance of novel graphene-based devices often strongly depends on the electrical quality of the supporting oxide. To elucidate the general governing principles underlying this behavior, we use first-principles simulations to generate representative classes of experimentally known defect centers in passivated silicon dioxide substrates and study their charge transfer with adsorbed graphene. We find that many of the open-shell structural perturbations generated near the interface self-passivate during annealing, leading to occupied-unoccupied pairs of midgap states in the silicon dioxide band structure, but no doping of the graphene occurs. However, dangling bonds or paramagnetic defect centers stable to thermal annealing do lead to partially occupied midgap energy states that are energetically misaligned with the Dirac point of graphene allowing charge to flow to or from the carbon layer. In particular, dangling oxygen bonds in the oxide strongly $p$ dope the graphene. We also study doping from charge donating impurities within the substrate lattice as these also act to limit the performance of graphene-based devices.

Received 4 June 2012

DOI:https://doi.org/10.1103/PhysRevB.86.041409

Authors & Affiliations

Razvan A. Nistor¹, Marcelo A. Kuroda¹, Ahmed A. Maarouf^1,2,3, and Glenn J. Martyna^1,*

¹IBM Research Division, T. J. Watson Research Center, P.O. Box 218, Yorktown Heights, New York 10598, USA
²Egypt Nanotechnology Center, Smart Village, Building 151, Giza 12577, Egypt
³Department of Physics, Faculty of Science, Cairo University, Giza 12613, Egypt

^*martyna@us.ibm.com

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Vol. 86, Iss. 4 — 15 July 2012

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Images

Figure 1
(a) The high-symmetry points of the hexagonal Brillouin zone of graphene along with a representation of the characteristic linear bands intersecting at the Dirac point (DP) which is concomitant with Fermi energy $E_{f}$ in undoped samples. Any shift of the Fermi level leads to $n$ or $p$ doping of the carbon layer. (b) Top view of the lattice matched $4 \times 4$ graphene sheet to the (001) face of the SiO $_{2}$ substrate. All atomic configurations are rendered using the Visual Molecular Dynamics software (Ref. 40). (c) Energy diagram of graphene on SiO $_{2}$ whose Dirac point energy $E_{D}$ lies far from the occupied valence ( $E_{V}$ ) and unoccupied conduction band ( $E_{C}$ ) edges of a fully passivated pristine SiO $_{2}$ substrate. (d) Open-shell defects within the oxide give rise to midgap defect states. When these partially occupied defect levels lie below $E_{D}$ , as is drawn here, charge flows from the graphene resulting in $p$ doping of the carbon layer ( $+ Q_{Gr}$ ).Reuse & Permissions
Figure 2
(a) Graphene on the passivated (001) face of SiO $_{2}$ . (b) Band structure of (a) with projected contributions from carbon $p_{z}$ states (circles). (c) Graphene on a defected SiO $_{2}$ sample in which a silicon vacancy is introduced in the oxide. All dangling bonds heal during thermalization by forming an extended peroxyl chain identified by the oxygen atoms numbered 1–3. (d) Band structure of (b) highlighting the appearance of occupied/unoccupied pairs of midgap oxygen states (squares) from the defect chain. No charge transfer to the graphene occurs. (e) Graphene on a defected SiO $_{2}$ sample with a dangling oxygen bond (labeled 1) formed in an oxygen-rich sample. Also shown (labeled 2, 3) is a resultant peroxyl chain. The space resolved local density of states (LDOS) is given by the surface around the defect sites and carbon plane. Strong $p$ doping of the graphene occurs. (f) Band structure of (e) showing the strong $p$ doping of the carbon layer (shift in $Δ E_{D}$ ). Also shown are the flat bands attributed to the dangling oxygen bond fixed at the Fermi level (diamonds) and oxygen bands from the peroxyl chain (squares).Reuse & Permissions
Figure 3
(a) Boron impurity replacing a silicon atom in SiO $_{2}$ . The LDOS is localized around the neighboring oxygens labeled 1–4 (an isosurface value of 0.7 a.u. is used so only contributions around the defect site are emphasized). (b) Band structure of (a) with projected carbon $p_{z}$ contributions (circles), neighboring oxygen states (squares), and boron states (down triangles). (c) Phosphorus impurity replacing a silicon atom in SiO $_{2}$ . The LDOS is localized around the impurity and neighboring oxygens are labeled 1–4. (d) Band structure of (c) with projected carbon $p_{z}$ contributions (circles), neighboring oxygen states (squares), and phosphorus states localized around the Fermi level located at 0 eV (up triangles).Reuse & Permissions

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