7 research outputs found
Unravelling the role of inelastic tunneling into pristine and defected graphene
We present a first principles method for calculating the inelastic electron
tunneling spectroscopy (IETS) on gated graphene. We reproduce experiments on
pristine graphene and point out the importance of including several phonon
modes to correctly estimate the local doping from IETS. We demonstrate how the
IETS of typical imperfections in graphene can yield characteristic fingerprints
revealing e.g. adsorbate species or local buckling. Our results show how care
is needed when interpreting STM images of defects due to suppression of the
elastic tunneling on graphene
First-principles electron transport with phonon coupling: Large scale at low cost
Phonon-assisted tunneling plays a crucial role for electronic device
performance and even more so with future size down-scaling. We show how one can
include this effect in large-scale first-principles calculations using a single
"special thermal displacement" (STD) of the atomic coordinates at almost the
same cost as elastic transport calculations. We apply the method to
ultra-scaled silicon devices and demonstrate the importance of phonon-assisted
band-to-band and source-to-drain tunneling. In a diode the phonons lead to a
rectification ratio suppression in good agreement with experiments, while in an
ultra-thin body transistor the phonons increase off-currents by four orders of
magnitude, and the subthreshold swing by a factor of four, in agreement with
perturbation theory
QuantumATK: An integrated platform of electronic and atomic-scale modelling tools
QuantumATK is an integrated set of atomic-scale modelling tools developed
since 2003 by professional software engineers in collaboration with academic
researchers. While different aspects and individual modules of the platform
have been previously presented, the purpose of this paper is to give a general
overview of the platform. The QuantumATK simulation engines enable
electronic-structure calculations using density functional theory or
tight-binding model Hamiltonians, and also offers bonded or reactive empirical
force fields in many different parametrizations. Density functional theory is
implemented using either a plane-wave basis or expansion of electronic states
in a linear combination of atomic orbitals. The platform includes a long list
of advanced modules, including Green's-function methods for electron transport
simulations and surface calculations, first-principles electron-phonon and
electron-photon couplings, simulation of atomic-scale heat transport, ion
dynamics, spintronics, optical properties of materials, static polarization,
and more. Seamless integration of the different simulation engines into a
common platform allows for easy combination of different simulation methods
into complex workflows. Besides giving a general overview and presenting a
number of implementation details not previously published, we also present four
different application examples. These are calculations of the phonon-limited
mobility of Cu, Ag and Au, electron transport in a gated 2D device, multi-model
simulation of lithium ion drift through a battery cathode in an external
electric field, and electronic-structure calculations of the
composition-dependent band gap of SiGe alloys.Comment: Submitted to Journal of Physics: Condensed Matte