3,056 research outputs found
Optical properties of arrays of quantum dots with internal disorder
Optical properties of large arrays of isolated quantum dots are discussed in
order to interpret the existent photoluminescence data. The presented theory
explains the large observed shift between the lowest emission and absorption
energies as the average distance between the ground and first excited states of
the dots. The lineshape of the spectra is calculated for the case when the
fluctuations of the energy levels in quantum dots are due to the alloy
composition fluctuations. The calculated lineshape is in good agreement with
the experimental data. The influence of fluctuations of the shape of quantum
dots on the photoluminescence spectra is also discussed.Comment: 7 pages (twocolumn) LATEX, 6 Postscript figure
Fano interference effect on the transition spectrum of single electron transistors
We theoretically study the intraband transition spectrum of single electron
transistors (SETs) composed of individual self-assembled quantum dots. The
polarization of SETs is obtained by using the nonequilibrium Green's function
technique and the Anderson model with three energy levels. Owing to
nonradiative coupling between two excited states through the continuum of
electrodes, the Fano interference effect significantly influences the peak
position and intensity of infrared wavelength single-photon spectrum.Comment: 4 pages, 5 figure
Scanning Fourier Spectroscopy: A microwave analog study to image transmission paths in quantum dots
We use a microwave cavity to investigate the influence of a movable absorbing
center on the wave function of an open quantum dot. Our study shows that the
absorber acts as a position-selective probe, which may be used to suppress
those wave function states that exhibit an enhancement of their probability
density near the region where the impurity is located. For an experimental
probe of this wave function selection, we develop a technique that we refer to
as scanning Fourier spectroscopy, which allows us to identify, and map out, the
structure of the classical trajectories that are important for transmission
through the cavity.Comment: 4 pages, 5 figure
Wave function mapping conditions in Open Quantum Dots structures
We discuss the minimal conditions for wave function spectroscopy, in which
resonant tunneling is the measurement tool. Two systems are addressed: resonant
tunneling diodes, as a toy model, and open quantum dots. The toy model is used
to analyze the crucial tunning between the necessary resolution in
current-voltage characteristics and the breakdown of the wave functions probing
potentials into a level splitting characteristic of double quantum wells. The
present results establish a parameter region where the wavefunction
spectroscopy by resonant tunneling could be achieved. In the case of open
quantum dots, a breakdown of the mapping condition is related to a change into
a double quantum dot structure induced by the local probing potential. The
analogy between the toy model and open quantum dots show that a precise control
over shape and extention of the potential probes is irrelevant for wave
function mapping. Moreover, the present system is a realization of a tunable
Fano system in the wave function mapping regime.Comment: 6 pages, 6 figure
Investigation of reactive‐ion‐etch‐induced damage of InP/InGaAs multiple quantum wells by photoluminescence
The effects of CH4/H2 reactive ion etching (RIE) on the optical properties of an InP/InGaAs multiple‐quantum‐well structure have been investigated by low‐temperature photoluminescence (PL). The structure consisted of eight InGaAs quantum wells, lattice matched to InP, with nominal thicknesses of 0.5, 1, 2, 3, 5, 10, 20, and 70 monolayers, respectively, on top of a 200‐nm‐thick layer of InGaAs for calibration. The design of this structure allowed etch‐induced damage depth to be obtained from the PL spectra due to the different confinement energies of the quantum wells. The samples showed no significant decrease of luminescence intensity after RIE. However, the observed shift and broadening of the PL peaks from the quantum wells indicate that intermixing of well and barrier material increased with etch time. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70403/2/JAPIAU-78-3-1528-1.pd
Eight-band calculations of strained InAs/GaAs quantum dots compared with one, four, and six-band approximations
The electronic structure of pyramidal shaped InAs/GaAs quantum dots is
calculated using an eight-band strain dependent Hamiltonian. The
influence of strain on band energies and the conduction-band effective mass are
examined. Single particle bound-state energies and exciton binding energies are
computed as functions of island size. The eight-band results are compared with
those for one, four and six bands, and with results from a one-band
approximation in which m(r) is determined by the local value of the strain. The
eight-band model predicts a lower ground state energy and a larger number of
excited states than the other approximations.Comment: 8 pages, 7 figures, revtex, eps
How quantum bound states bounce and the structure it reveals
We investigate how quantum bound states bounce from a hard surface. Our
analysis has applications to ab initio calculations of nuclear structure and
elastic deformation, energy levels of excitons in semiconductor quantum dots
and wells, and cold atomic few-body systems on optical lattices with sharp
boundaries. We develop the general theory of elastic reflection for a composite
body from a hard wall. On the numerical side we present ab initio calculations
for the compression of alpha particles and universal results for two-body
states. On the analytical side we derive a universal effective potential that
gives the reflection scattering length for shallow two-body states.Comment: final publication version, new lattice results on alpha particle
compression, 5 pages, 2 figure
Electronic structure of strained InP/GaInP quantum dots
We calculate the electronic structure of nm scale InP islands embedded in
. The calculations are done in the envelope approximation
and include the effects of strain, piezoelectric polarization, and mixing among
6 valence bands. The electrons are confined within the entire island, while the
holes are confined to strain induced pockets. One pocket forms a ring at the
bottom of the island near the substrate interface, while the other is above the
island in the GaInP. The two sets of hole states are decoupled. Polarization
dependent dipole matrix elements are calculated for both types of hole states.Comment: Typographical error corrected in strain Hamiltonia
Effect of deconfinement on resonant transport in quantum wires
The effect of deconfinement due to finite band offsets on transport through
quantum wires with two constrictions is investigated. It is shown that the
increase in resonance linewidth becomes increasingly important as the size is
reduced and ultimately places an upper limit on the energy (temperature) scale
for which resonances may be observed.Comment: 6 pages, 6 postscript files with figures; uses REVTe
Multi-Exciton Spectroscopy of a Single Self Assembled Quantum Dot
We apply low temperature confocal optical microscopy to spatially resolve,
and spectroscopically study a single self assembled quantum dot. By comparing
the emission spectra obtained at various excitation levels to a theoretical
many body model, we show that: Single exciton radiative recombination is very
weak. Sharp spectral lines are due to optical transitions between confined
multiexcitonic states among which excitons thermalize within their lifetime.
Once these few states are fully occupied, broad bands appear due to transitions
between states which contain continuum electrons.Comment: 12 pages, 4 figures, submitted for publication on Jan,28 199
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