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Pedersen T.G.,University of Aalborg | Pedersen T.G.,Center for Nanostructured Graphene | Pedersen J.G.,University of Aalborg
Journal of Applied Physics | Year: 2012

Periodic arrays of antidots, i.e., nanoscale perforations, in graphene enable tight confinement of carriers and efficient transport barriers. Such barriers evade the Klein tunneling mechanism by being of the mass rather than electrostatic type. While all graphene antidot lattices (GALs) may support directional barriers, we show, however, that a full transport gap exists only for certain orientations of the GAL. Moreover, we assess the applicability of gapped graphene and the Dirac continuum approach as simplified models of various antidot structures showing that, in particular, the former is an excellent approximation for transport in GALs supporting a bulk band gap. Finally, the transport properties of a GAL based resonant tunneling diode are analyzed indicating that such advanced graphene based devices may, indeed, be realized using GAL structures. © 2012 American Institute of Physics.


Pedersen T.G.,University of Aalborg | Pedersen T.G.,Center for Nanostructured Graphene
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

Dopants positioned near edges in nanostructured graphene behave differently from bulk dopants. Most notable, the amount of charge transferred to delocalized states (i.e., doping efficiency) depends on position as well as edge chirality. We apply a self-consistent tight-binding model to analyze this problem focusing on substitutional nitrogen and boron doping. Using a Green's-function technique, very large structures can be studied, and artificial interactions between dopants in periodically repeated simulations cells are avoided. We find pronounced signatures of edges in the local impurity density of states. Importantly, the doping efficiency is found to oscillate with sublattice position, in particular, for dopants near zigzag edges. Finally, to assess the effect of electron-electron interactions, we compute the self-energy corrected Green's function. © 2015 American Physical Society.


Pedersen T.G.,University of Aalborg | Pedersen T.G.,Center for Nanostructured Graphene | Pedersen J.G.,Technical University of Denmark
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Boron and nitrogen substitutional impurities in graphene are analyzed using a self-consistent tight-binding approach. An analytical result for the impurity Green's function is derived taking broken electron-hole symmetry into account and validated by comparison to numerical diagonalization. The impurity potential depends sensitively on the impurity occupancy, leading to a self-consistency requirement. We solve this problem using the impurity Green's function and determine the self-consistent local density of states at the impurity site and, thereby, identify acceptor and donor energy resonances. © 2013 American Physical Society.


Pedersen T.G.,University of Aalborg | Pedersen T.G.,Center for Nanostructured Graphene
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

A theory for the nonlinear excitonic optical response of semiconductors is developed. By adopting the length gauge, intraband effects are rigorously taken into account. We show that the second-order nonlinear response mixing intra- and interband transitions can be expressed in terms of generalized derivatives of the exciton Green's function. The theory is applied to hexagonal boron-nitride monolayers. For both the linear and nonlinear response, a dramatic influence of excitons is found. Hence, new discrete resonances appear as well as pronounced changes in the continuum spectrum. © 2015 American Physical Society.


Brun So.J.,University of Aalborg | Brun So.J.,Center for Nanostructured Graphene | Pereira V.M.,National University of Singapore | Pedersen T.G.,University of Aalborg | Pedersen T.G.,Center for Nanostructured Graphene
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

Bottom-up fabrication of graphene antidot lattices (GALs) has previously yielded atomically precise structures with subnanometer periodicity. Focusing on this type of experimentally realized GAL, we perform density functional theory calculations on the pristine structure as well as GALs with edge carbon atoms substituted with boron or nitrogen. We show that p- and n-type doping levels emerge with activation energies that depend on the level of hydrogenation at the impurity. Furthermore, a tight-binding parametrization together with a Green's function method are used to describe more dilute doping. Finally, random configurations of impurities in moderately doped systems are considered to show that the doping properties are robust against disorder. © 2016 American Physical Society.

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