203 research outputs found
Theoretical study of scattering in graphene ribbons in the presence of structural and atomistic edge roughness
We investigate the diffusive electron-transport properties of charge-doped
graphene ribbons and nanoribbons with imperfect edges. We consider different
regimes of edge scattering, ranging from wide graphene ribbons with (partially)
diffusive edge scattering to ribbons with large width variations and
nanoribbons with atomistic edge roughness. For the latter, we introduce an
approach based on pseudopotentials, allowing for an atomistic treatment of the
band structure and the scattering potential, on the self-consistent solution of
the Boltzmann transport equation within the relaxation-time approximation and
taking into account the edge-roughness properties and statistics. The resulting
resistivity depends strongly on the ribbon orientation, with zigzag (armchair)
ribbons showing the smallest (largest) resistivity and intermediate ribbon
orientations exhibiting intermediate resistivity values. The results also show
clear resistivity peaks, corresponding to peaks in the density of states due to
the confinement-induced subband quantization, except for armchair-edge ribbons
that show a very strong width dependence because of their claromatic behavior.
Furthermore, we identify a strong interplay between the relative position of
the two valleys of graphene along the transport direction, the correlation
profile of the atomistic edge roughness, and the chiral valley modes, leading
to a peculiar strongly suppressed resistivity regime, most pronounced for the
zigzag orientation.Comment: 13 pages, 7 figure
Generalized phonon-assisted Zener tunneling in indirect semiconductors with non-uniform electric fields : a rigorous approach
A general framework to calculate the Zener current in an indirect
semiconductor with an externally applied potential is provided. Assuming a
parabolic valence and conduction band dispersion, the semiconductor is in
equilibrium in the presence of the external field as long as the electronphonon
interaction is absent. The linear response to the electron-phonon interaction
results in a non-equilibrium system. The Zener tunneling current is calculated
from the number of electrons making the transition from valence to conduction
band per unit time. A convenient expression based on the single particle
spectral functions is provided, enabling the numerical calculation of the Zener
current under any three-dimensional potential profile. For a one dimensional
potential profile an analytical expression is obtained for the current in a
bulk semiconductor, a semiconductor under uniform field and a semiconductor
under a non-uniform field using the WKB (Wentzel-Kramers-Brillouin)
approximation. The obtained results agree with the Kane result in the low field
limit. A numerical example for abrupt p - n diodes with different doping
concentrations is given, from which it can be seen that the uniform field model
is a better approximation than the WKB model but a direct numerical treatment
is required for low bias conditions.Comment: 29 pages, 7 figure
Image-Force Barrier Lowering of Schottky Barriers in Two-Dimensional Materials as a Function of Metal Contact Angle
Two-dimensional (2D) semiconductors are a promising solution for the
miniaturization of electronic devices and for the exploration of novel physics.
However, practical applications and demonstrations of physical phenomena are
hindered by high Schottky barriers at the contacts to 2D semiconductors. While
the process of image-force barrier lowering (IFBL) can considerably decrease
the Schottky barrier, IFBL is not fully understood for the majority of
prevalent contact geometries. We introduce a novel technique to determine the
IFBL potential energy with application spanning far beyond that of any existing
method. We do so by solving Poisson's equation with the boundary conditions of
two metal surfaces separated by an angle Omega. We then prove that our result
can also be obtained with the method of images provided a non-Euclidean,
cone-manifold space is used. The resulting IFBL is used to calculate the
expected contact resistance of the most prevalent geometric contacts. Finally,
we investigate contact resistance and show how the stronger IFBL counteracts
the effect of larger depletion width with increasing contact angle. We find
that top contacts experience lower contact resistance than edge contacts.
Remarkably, our results identify tunable parameters for reducing Schottky
barriers and likewise contact resistance to edge-contacted 2D materials,
enhancing potential applications.Comment: 22 pages, 6 figure
On the Impact of the Assimilation of Nacelle Winds and Yaw Angles With WRF-FDDA and WRF-DART for Short-Term Wind Energy Predictions
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