196,673 research outputs found
Correlations between Optical Properties and Voronoi-Cell Area of Quantum Dots
A semiconductor quantum dot (QD) can generate highly indistinguishable
single-photons at a high rate. For application in quantum communication and
integration in hybrid systems, control of the QD optical properties is
essential. Understanding the connection between the optical properties of a QD
and the growth process is therefore important. Here, we show for GaAs QDs,
grown by infilling droplet-etched nano-holes, that the emission wavelength, the
neutral-to-charged exciton splitting, and the diamagnetic shift are strongly
correlated with the capture zone-area, an important concept from nucleation
theory. We show that the capture-zone model applies to the growth of this
system even in the limit of a low QD-density in which atoms diffuse over
m-distances. The strong correlations between the various QD parameters
facilitate preselection of QDs for applications with specific requirements on
the QD properties; they also suggest that a spectrally narrowed QD distribution
will result if QD growth on a regular lattice can be achieved
Electron transport and terahertz gain in quantum-dot cascades
Electron transport through quantum-dot (QD) cascades was investigated using the formalism of nonequilibrium Green's functions within the self-consistent Born approximation. Polar coupling to optical phonons, deformation potential coupling to acoustic phonons, as well as anharmonic decay of longitudinal optical phonons were included in the simulation. A QD cascade laser structure comprising two QDs per period was designed and its characteristics were simulated. Significant values of population inversion enabling lasing in the terahertz frequency range were predicted, with operating current densities being more than an order of magnitude smaller than in existing terahertz quantum-well-based quantum-cascade lasers
Extraordinary Temperature Dependence of the Resonant Andreev Reflection
An extraordinary temperature dependence of the resonant Andreev reflection
via discrete energy level in a normal-metal / quantum-dot / superconductor
(N-QD-S) system is predicted theoretically by using Green function technique.
The width of zero bias conductance peak in N-QD-S is about and does not exhibit thermal broadening, where and
are the coupling strength between QD and leads. Considering the
intra-dot Coulomb interaction, the Coulomb blockade oscillations conducted by
Andreev reflection differs dramatically from that in N-QD-N. Instead of thermal
broadening, finite temperature induces more resonant peaks around the
oscillation peaks of zero temperature. This effect can be applied to determine
the coupling strength and QD level spacing in N-QD-S.Comment: 11 pages, 3 figures, LaTe
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