Electronic Properties of Silicon Nanowires: Confined Phonons and Surface Roughness (original) (raw)
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Carrier-phonon interaction in small cross-sectional silicon nanowires
Journal of Applied Physics, 2008
Using first-order perturbation theory and deformation potential approximation, the interaction of electrons and holes with acoustic and optical phonons is investigated in silicon nanowires ͑SiNWs͒ with different diameters and crystallographic axis orientations. The electronic band structures for ͓110͔ and ͓100͔ SiNWs are obtained from a sp 3 d 5 s ء tight-binding scheme, while a continuum model is assumed for phonon dispersion. The influence of confined and bulk phonons on carrier transport is investigated.
Electronic properties of silicon nanowires
Electron Devices, …, 2005
The electronic structure and transmission coefficients of Si nanowires are calculated in a 3 5 model. The effect of wire thickness on the bandgap, conduction valley splitting, hole band splitting, effective masses, and transmission is demonstrated. Results from the 3 5 model are compared to those from a single-band effective mass model to assess the validity of the singleband effective mass model in narrow Si nanowires. The one-dimensional Brillouin zone of a Si nanowire is direct gap. The conduction band minimum can split into a quartet of energies although often two of the energies are degenerate. Conduction band valley splitting reduces the averaged mobility mass along the axis of the wire, but quantum confinement increases the transverse mass of the conduction band edge. Quantum confinement results in a large increase in the hole masses of the two highest valence bands. A single-band model performs reasonably well at calculating the effective band edges for wires as small as 1.54-nm square. A wiresubstrate interface can be viewed as a heterojunction with band offsets resulting in reflection in the transmission.
Journal of Applied Physics, 2008
We investigate the effects of electron and acoustic-phonon confinement on the low-field electron mobility of thin square silicon nanowires (SiNWs) that are surrounded by SiO2 and gated. We employ a self-consistent Poisson-Schrödinger-Monte Carlo solver that accounts for scattering due to acoustic phonons (confined and bulk), intervalley phonons, and the Si/SiO2 surface roughness. The wires considered have cross sections between 3 × 3 nm 2 and 8 × 8 nm 2 . For larger wires, as expected, the dependence of the mobility on the transverse field from the gate is pronounced. At low transverse fields, where phonon scattering dominates, scattering from confined acoustic phonons results in about a 10% decrease of the mobility with respect to the bulk phonon approximation. As the wire cross-section decreases, the electron mobility drops because the detrimental increase in both electron-acoustic phonon and electron-surface roughness scattering rates overshadows the beneficial volume inversion and subband modulation. For wires thinner than 5 × 5 nm 2 , surface roughness scattering dominates regardless of the transverse field applied and leads to a monotonic decrease of the electron mobility with decreasing SiNWs cross section.
Electronic and transport properties of silicon nanowires
Journal of Computational Electronics, 2007
The electronic, structural and transport properties of silicon nanowires have been investigated with different approaches. The Empirical Tight-Binding model (ETB) and Linear Combination of Bulk Bands (LCBB) method are used to calculate effect of quantum confinement on electronic energies, bandgap and effective masses in silicon nanowires in function of Si cell size. Both hydrogenated and SiO2 terminated silicon surfaces are studied. Transport properties of nanowires are obtained by applying the Non-Equilibrium Green Function (NEGF) method. NEGF approach has been used to describe nanoMOSFET devices based on Silicon nanowires.
Phonon Engineering in Isotopically Disordered Silicon Nanowires
Nano Letters, 2015
The introduction of stable isotopes in the fabrication of semiconductor nanowires provides an additional degree of freedom to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. With this perspective, we report on phonon engineering in metalcatalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors 28 SiH 4 , 29 SiH 4 , and 30 SiH 4 with purity better than 99.9%. More specifically, isotopically mixed nanowires 28 Si x 30 Si 1−x with a composition close to the highest mass disorder (x ∼ 0.5) were investigated. The effect of mass disorder on the phonon behavior was elucidated and compared to that in isotopically pure 29 Si nanowires having a similar reduced mass. We found that the disorder-induced enhancement in phonon scattering in isotopically mixed nanowires is unexpectedly much more significant than in bulk crystals of close isotopic compositions. This effect is explained by a nonuniform distribution of 28 Si and 30 Si isotopes in the grown isotopically mixed nanowires with local compositions ranging from x = ∼0.25 to 0.70. Moreover, we also observed that upon heating, phonons in 28 Si x 30 Si 1−x nanowires behave remarkably differently from those in 29 Si nanowires suggesting a reduced thermal conductivity induced by mass disorder. Using Raman nanothermometry, we found that the thermal conductivity of isotopically mixed 28 Si x 30 Si 1−x nanowires is ∼30% lower than that of isotopically pure 29 Si nanowires in agreement with theoretical predictions.
2016
We study the effect of confinement on the phonon properties of ultra-narrow silicon nanowires of side sizes of 110nm. We use the modified valence force field method to compute the phononic dispersion, and extract the density of states, the transmission function, the sound velocity, the ballistic thermal conductance and boundary scattering-limited diffusive thermal conductivity. We find that the phononic dispersion and the ballistic thermal conductance are functions of the geometrical features of the structures, i.e. the transport orientation and confinement dimension. The phonon group velocity and thermal conductance can vary by a factor of two depending on the geometrical features of the channel. The <110> nanowire has the highest group velocity and thermal conductance, whereas the <111> the lowest. The <111> channel is thus the most suitable orientation for thermoelectric devices based on Si nanowires since it also has a large power factor. Our findings could be ...
Electronic Structures and Band Gap of Doped Silicon Nanowires (SiNWs)
Empirical tight binding parameters are used to find out the electronic properties of Silicon nanowires (SiNWs) for different crystal orientation, cross-sectional size and shape by using nearest neighbor sp 3 d 5 s* atomic orbital basis. The three different color atoms are Silicon and at the end the black atoms are hydrogen which are shown in any of the diagrams. The nanowire growth direction is x which is into (or out of) the paper. The other directions y and z are < 010 > and <001>, respectively for the <100> wires, and <110> and <001>, respectively for the <110> wires. The cross section of <100> wire looks rectangular. The unit cell is 0.543 nm long and has 4 atomic layers. The <110> nanowire looks hexagonal. It has 2 atomic layers in a 0.384 nm unit cell. It has been calculated that for circular Si nanowire the conduction band minima = 1.58027eV; valence band maxima =-0.378968eV so the band gap of circular Si nanowire = 1.95924eV. Similarly for rectangular Si nanowire the conduction band minima = 1.52038eV; valence band maxima =-0.282514eV; and the band gap of rectangular Si nanowire = 1.8029eV. Likewise for triangular Si nanowire the conduction band minima = 1.85684eV; valence band maxima =-0.531543eV; and the band gap of triangular Si nanowire = 2.38838eV.
Electron Transport in Si Nanowires
Journal of Physics: Conference Series, 2006
We investigate electron transport in silicon nanowires taking into account acoustic, non-polar optical phonons and surface/interface roughness scattering. We find that at very high transverse fields the reduced density of final states to which the carriers can scatter into gives rise to a reduced influence of interface-roughness scattering, which is promising result from a fabrication point of view.