668 research outputs found
Enhanced thermoelectric figure of merit in vertical graphene junctions
In this work, we investigate thermoelectric properties of junctions
consisting of two partially overlapped graphene sheets coupled to each other in
the cross-plane direction. It is shown that because of the weak van-der Waals
interactions between graphene layers, the phonon conductance in these junctions
is strongly reduced, compared to that of single graphene layer structures,
while their electrical performance is weakly affected. By exploiting this
effect, we demonstrate that the thermoelectric figure of merit can reach values
higher than 1 at room temperature in junctions made of gapped graphene
materials, for instance, graphene nanoribbons and graphene nanomeshes. The
dependence of thermoelectric properties on the junction length is also
discussed. This theoretical study hence suggests an efficient way to enhance
thermoelectric efficiency of graphene devices.Comment: 6 pages, 4 figures, submitte
Effect of discrete impurities on electron transport in ultra-short MOSFET using 3D Monte Carlo simulation
This paper discusses the influence of the channel impurity distribution on
the transport and the drive current in short-gate MOSFET. In this purpose, a
careful description of electron-ion interaction suitable for the case of
discrete impurities has been implemented in a 3D particle Monte Carlo
simulator. This transport model is applied to the investigation of 50 nm MOSFET
operation. The results show that a small change in the number of doping
impurities or in the position of a single discrete impurity in the inversion
layer may significantly influence the drain current. This effect is not only
related to threshold voltage fluctuations but also to variations in transport
properties in the inversion layer, especially at high drain voltage. The
results are analyzed in terms of local fluctuations of electron velocity and
current density. In a set of fifteen simulated devices the drive current Ion,
determined at VGS = VDS = 0.6 V, is found to vary in a range of 23% according
to the position of channel impurities.Comment: 31 pages, 13 figures, revised version: discussions and references
added, to be published in IEEE Trans. Electron. Device
Electron transport properties in high-purity Ge down to cryogenic temperatures
Electron transport in Ge at various temperatures down to 20 mK has been
investigated using particle Monte Carlo simulation taking into account ionized
impurity and inelastic phonon scattering. The simulations account for the
essential features of electron transport at cryogenic temperature: Ohmic
regime, anisotropy of the drift velocity relative to the direction of the
electric field, as well as a negative differential mobility phenomenon along
the field orientation. Experimental data for the electron velocities are
reproduced with a satisfactory accuracy. Examples of electron position in the
real space during the simulations are given and evidence separated clouds of
electrons propagating along different directions depending on the valley they
belong.Comment: 24 pages, 11 figure
Monte Carlo study of coaxially gated CNTFETs: capacitive effects and dynamic performance
Carbon Nanotube (CNT) appears as a promising candidate to shrink field-effect
transistors (FET) to the nanometer scale. Extensive experimental works have
been performed recently to develop the appropriate technology and to explore DC
characteristics of carbon nanotube field effect transistor (CNTFET). In this
work, we present results of Monte Carlo simulation of a coaxially gated CNTFET
including electron-phonon scattering. Our purpose is to present the intrinsic
transport properties of such material through the evaluation of electron
mean-free-path. To highlight the potential of high performance level of CNTFET,
we then perform a study of DC characteristics and of the impact of capacitive
effects. Finally, we compare the performance of CNTFET with that of Si nanowire
MOSFET.Comment: 15 pages, 14 figures, final version to be published in C. R. Acad.
Sci. Pari
n-Si/SiGe quantum cascade structures for THz emission
In this work we report on modelling the electron transport in n-Si/SiGe structures. The
electronic structure is calculated within the effective-mass complex-energy framework,
separately for perpendicular (Xz) and in-plane (Xxy) valleys, the degeneracy of which is
lifted by strain, and additionally by size quantization. The transport is described via
scattering between quantized states, using the rate equations approach and tight-binding
expansion, taking the coupling with two nearest-neighbour periods. The acoustic phonon,
optical phonon, alloy and interface roughness scattering are taken in the model. The
calculated U/I dependence and gain profiles are presented for a couple of QC structures
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