87 research outputs found
Inelastic vibrational signals in electron transport across graphene nanoconstrictions
We present calculations of the inelastic vibrational signals in the
electrical current through a graphene nanoconstriction. We find that the
inelastic signals are only present when the Fermi-level position is tuned to
electron transmission resonances, thus, providing a fingerprint which can link
an electron transmission resonance to originate from the nanoconstriction. The
calculations are based on a novel first-principles method which includes the
phonon broadening due to coupling with phonons in the electrodes. We find that
the signals are modified due to the strong coupling to the electrodes, however,
still remain as robust fingerprints of the vibrations in the nanoconstriction.
We investigate the effect of including the full self-consistent potential drop
due to finite bias and gate doping on the calculations and find this to be of
minor importance
First-principles method for electron-phonon coupling and electron mobility: Applications to 2D materials
We present density functional theory calculations of the phonon-limited
mobility in n-type monolayer graphene, silicene and MoS. The material
properties, including the electron-phonon interaction, are calculated from
first-principles. We provide a detailed description of the normalized full-band
relaxation time approximation for the linearized Boltzmann transport equation
(BTE) that includes inelastic scattering processes. The bulk electron-phonon
coupling is evaluated by a supercell method. The method employed is fully
numerical and does therefore not require a semi-analytic treatment of part of
the problem and, importantly, it keeps the anisotropy information stored in the
coupling as well as the band structure. In addition, we perform calculations of
the low-field mobility and its dependence on carrier density and temperature to
obtain a better understanding of transport in graphene, silicene and monolayer
MoS. Unlike graphene, the carriers in silicene show strong interaction with
the out-of-plane modes. We find that graphene has more than an order of
magnitude higher mobility compared to silicene. For MoS, we obtain several
orders of magnitude lower mobilities in agreement with other recent theoretical
results. The simulations illustrate the predictive capabilities of the newly
implemented BTE solver applied in simulation tools based on first-principles
and localized basis sets
Efficient first-principles calculation of phonon assisted photocurrent in large-scale solar cell devices
We present a straightforward and computationally cheap method to obtain the
phonon-assisted photocurrent in large-scale devices from first-principles
transport calculations. The photocurrent is calculated using nonequilibrium
Green's function with light-matter interaction from the first-order Born
approximation while electron-phonon coupling (EPC) is included through special
thermal displacements (STD). We apply the method to a silicon solar cell device
and demonstrate the impact of including EPC in order to properly describe the
current due to the indirect band-to-band transitions. The first-principles
results are successfully compared to experimental measurements of the
temperature and light intensity dependence of the open-circuit voltage of a
silicon photovoltaic module. Our calculations illustrate the pivotal role
played by EPC in photocurrent modelling to avoid underestimation of the
open-circuit voltage, short-circuit current and maximum power. This work
represents a recipe for computational characterization of future photovoltaic
devices including the combined effects of light-matter interaction,
phonon-assisted tunneling and the device potential at finite bias from the
level of first-principles simulations
Origin Of Current-Induced Forces In An Atomic Gold Wire: A First Principles Study
We address the microscopic origin of the current-induced forces by analyzing
results of first principles density functional calculations of atomic gold
wires connected to two gold electrodes with different electrochemical
potentials. We find that current induced forces are closely related to the
chemical bonding, and arise from the rearrangement of bond charge due to the
current flow. We explain the current induced bond weakening/strengthening by
introducing bond charges decomposed into electrode components.Comment: 4 pages, 4 figure
Atomic-scale model for the contact resistance of the nickel-graphene interface
We perform first-principles calculations of electron transport across a
nickel-graphene interface. Four different geometries are considered, where the
contact area, graphene and nickel surface orientations and the passivation of
the terminating graphene edge are varied. We find covalent bond formation
between the graphene layer and the nickel surface, in agreement with other
theoretical studies. We calculate the energy-dependent electron transmission
for the four systems and find that the systems have very similar edge contact
resistance, independent of the contact area between nickel and graphene, and in
excellent agreement with recent experimental data. A simple model where
graphene is bonded with a metal surface shows that the results are generic for
covalently bonded graphene, and the minimum attainable edge contact resistance
is twice the ideal edge quantum contact resistance of graphene.Comment: 12 pages, 6 figure
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