20 research outputs found
Effect of wetting layers on the strain and electronic structure of InAs self-assembled quantum dots
The effect of wetting layers on the strain and electronic structure of InAs
self-assembled quantum dots grown on GaAs is investigated with an atomistic
valence-force-field model and an empirical tight-binding model. By comparing a
dot with and without a wetting layer, we find that the inclusion of the wetting
layer weakens the strain inside the dot by only 1% relative change, while it
reduces the energy gap between a confined electron and hole level by as much as
10%. The small change in the strain distribution indicates that strain relaxes
only little through the thin wetting layer. The large reduction of the energy
gap is attributed to the increase of the confining-potential width rather than
the change of the potential height. First-order perturbation calculations or,
alternatively, the addition of an InAs disk below the quantum dot confirm this
conclusion. The effect of the wetting layer on the wave function is
qualitatively different for the weakly confined electron state and the strongly
confined hole state. The electron wave function shifts from the buffer to the
wetting layer, while the hole shifts from the dot to the wetting layer.Comment: 14 pages, 3 figures, and 3 table
Effects of broadening and electron overheating in tunnel structures based on metallic clusters
We study the influence of energy levels broadening and electron subsystem
overheating in island electrode (cluster) on current-voltage characteristics of
three-electrode structure. A calculation scheme for broadening effect in
one-dimensional case is suggested. Estimation of broadening is performed for
electron levels in disc-like and spherical gold clusters. Within the
two-temperature model of metallic cluster and by using a size dependence of the
Debye frequency the effective electron temperature as a function of bias
voltage is found approximately. We suggest that the effects of broadening and
electron overheating are responsible for the strong smoothing of
current-voltage curves, which is observed experimentally at low temperatures in
structures based on clusters consisting of accountable number of atoms.Comment: 8 pages, 5 figure
Efficient thermoelectric energy conversion on quasi-localized electron states in diameter modulated nanowires
It is known that the thermoelectric efficiency of nanowires increases when their diameter decreases. Recently, we proposed that increase of the thermoelectric efficiency could be achieved by modulating the diameter of the nanowires. We showed that the electron thermoelectric properties depend strongly on the geometry of the diameter modulation. Moreover, it has been shown by another group that the phonon conductivity decreases in nanowires when they are modulated by dots. Here, the thermoelectric efficiency of diameter modulated nanowires is estimated, in the ballistic regime, by taking into account the electron and phonon transmission properties. It is demonstrated that quasi-localized states can be formed that are prosperous for efficient thermoelectric energy conversion
Phonons in Slow Motion: Dispersion Relations in Ultra-Thin Si Membranes
We report the changes in dispersion relations of hypersonic acoustic phonons
in free-standing silicon membranes as thin as \sim 8 nm. We observe a reduction
of the phase and group velocities of the fundamental flexural mode by more than
one order of magnitude compared to bulk values. The modification of the
dispersion relation in nanostructures has important consequences for noise
control in nano and micro-electromechanical systems (MEMS/NEMS) as well as
opto-mechanical devices.Comment: 5 page
Effect of external electric field on the probability of optical transitions in InGaAs/GaAs quantum wells
Nanoscale Imaging of Buried Structures via Scanning Near-Field
16. Materials and methods are available as supportin