31 research outputs found
Local Defects in colloidal quantum dot thin films measured via spatially resolved multi-modal optoelectronic spectroscopy.
The morphology, chemical composition, and electronic uniformity of thin-film solution-processed optoelectronics are believed to greatly affect device performance. Although scanning probe microscopies can address variations on the micrometer scale, the field of view is still limited to well under the typical device area, as well as the size of extrinsic defects introduced during fabrication. Herein, a micrometer-resolution 2D characterization method with millimeter-scale field of view is demonstrated, which simultaneously collects photoluminescence spectra, photocurrent transients, and photovoltage transients. This high-resolution morphology mapping is used to quantify the distribution and strength of the local optoelectronic property variations in colloidal quantum dot solar cells due to film defects, physical damage, and contaminants across nearly the entire test device area, and the extent to which these variations account for overall performance losses. It is found that macroscopic defects have effects that are confined to their localized areas, rarely prove fatal for device performance, and are largely not responsible for device shunting. Moreover, quantitative analysis based on statistical partitioning methods of such data is used to show how defect identification can be automated while identifying variations in underlying properties such as mobilities and recombination strengths and the mechanisms by which they govern device behavior.DMR-1807342 - National Science Foundation; Hopkins Extreme Materials InstituteAccepted manuscrip
A 674 nm external cavity diode laser for a ⁸⁸Sr⁺ ion trap
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 55-57).Atomic ion traps are a promising candidate for scalable quantum information processing. In this thesis, a 674 nm extended cavity diode laser is built to address an optical quantum bit in ⁸⁸Sr⁺ with the goal of testing such traps. To find this transition, a depletion experiment is performed in which the 674 nm transition depopulates the principal 422 nm transition, causing a dip in the ion fluorescence signal. Our preliminary results suggest that this depletion signal has been observed. .by Susanna M. Thon.S.B
Independent electrical tuning of separated quantum dots in coupled photonic crystal cavities
Systems of photonic crystal cavities coupled to quantum dots are a promising
architecture for quantum networking and quantum simulators. The ability to
independently tune the frequencies of laterally separated quantum dots is a
crucial component of such a scheme. Here, we demonstrate independent tuning of
laterally separated quantum dots in photonic crystal cavities coupled by
in-plane waveguides by implanting lines of protons which serve to electrically
isolate different sections of a diode structure.Comment: 3 pages, 3 figure
Strain-tuning of quantum dot optical transitions via laser-induced surface defects
We discuss the fine-tuning of the optical properties of self-assembled
quantum dots by the strain perturbation introduced by laser-induced surface
defects. We show experimentally that the quantum dot transition red-shifts,
independently of the actual position of the defect, and that such frequency
shift is about a factor five larger than the corresponding shift of a
micropillar cavity mode resonance. We present a simple model that accounts for
these experimental findings.Comment: 9 pages, 6 figures. To appear in Phys. Rev.
Dynamic modulation of photonic crystal nanocavities using gigahertz acoustic phonons
Photonic crystal membranes (PCM) provide a versatile planar platform for
on-chip implementations of photonic quantum circuits. One prominent quantum
element is a coupled system consisting of a nanocavity and a single quantum dot
(QD) which forms a fundamental building block for elaborate quantum information
networks and a cavity quantum electrodynamic (cQED) system controlled by single
photons. So far no fast tuning mechanism is available to achieve control within
the system coherence time. Here we demonstrate dynamic tuning by monochromatic
coherent acoustic phonons formed by a surface acoustic wave (SAW) with
frequencies exceeding 1.7 gigahertz, one order of magnitude faster than
alternative approaches. We resolve a periodic modulation of the optical mode
exceeding eight times its linewidth, preserving both the spatial mode profile
and a high quality factor. Since PCMs confine photonic and phononic
excitations, coupling optical to acoustic frequencies, our technique opens ways
towards coherent acoustic control of optomechanical crystals.Comment: 11 pages 4 figure
Tuning micropillar cavity birefringence by laser induced surface defects
We demonstrate a technique to tune the optical properties of micropillar
cavities by creating small defects on the sample surface near the cavity region
with an intense focused laser beam. Such defects modify strain in the
structure, changing the birefringence in a controllable way. We apply the
technique to make the fundamental cavity mode polarization-degenerate and to
fine tune the overall mode frequencies, as needed for applications in quantum
information science.Comment: RevTex, 7 pages, 4 figures (accepted for publication in Applied
Physics Letters
Optical modes in oxide-apertured micropillar cavities
We present a detailed experimental characterization of the spectral and
spatial structure of the confined optical modes for oxide-apertured micropillar
cavities, showing good-quality Hermite-Gaussian profiles, easily mode-matched
to external fields. We further derive a relation between the frequency
splitting of the transverse modes and the expected Purcell factor. Finally, we
describe a technique to retrieve the profile of the confining refractive index
distribution from the spatial profiles of the modes.Comment: 4 pages, 3 figure
Far-field emission profiles from L3 photonic crystal cavity modes
We experimentally characterize the spatial far-field emission profiles for
the two lowest confined modes of a photonic crystal cavity of the L3 type,
finding a good agreement with FDTD simulations. We then link the far-field
profiles to relevant features of the cavity mode near-fields, using a simple
Fabry-Perot resonator model. The effect of disorder on far-field cavity
profiles is clarified through comparison between experiments and simulations.
These results can be useful for emission engineering from active centers
embedded in the cavity.Comment: 9 pages, 7 figure