W. V. Schoenfeld

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Quantum communication relies on the availability of light pulses with strong quantum correlations among photons. An example of such an optical source is a single-photon pulse with a vanishing probability for detecting two or more photons. Using pulsed laser excitation of a single quantum dot, a single-photon turnstile device that generates a train of(More)
One promising path to a reduced cost of crystalline silicon (c-Si) photovoltaics (PV) is to increase silicon usage efficiency by using thinner wafers. Many challenges arise when transitioning to thin wafer cells, including increased surface recombination at the rear side of the cell, increased wafer bowing, and a reduction in optical absorption due to a(More)
Quantum dots or rings are artificial nanometre-sized clusters that confine electrons in all three directions. They can be fabricated in a semiconductor system by embedding an island of low-bandgap material in a sea of material with a higher bandgap. Quantum dots are often referred to as artificial atoms because, when filled sequentially with electrons, the(More)
To extend soft x-ray microscopy to a resolution of order 10 nm or better, we developed a new nanofabrication process for Fresnel zone plate lenses. The new process, based on the double patterning technique, has enabled us to fabricate high quality gold zone plates with 12 nm outer zones. Testing of the zone plate with the full-field transmission x-ray(More)
We propose a platform to achieve ultra-high Quality factor (Q) optical resonators based on semiconductor nanowires. By defining one-dimensional photonic crystal at nanowire ends and engineering the micro-cavity pattern, cavities with Q of 3×10 5 and mode volume smaller than 0.2(λ/n) 3 have been designed. This represents an increase of almost three orders of(More)
We report on the observation of photoluminescence from positive, neutral and negative charge states of single semiconductor quantum dots. For this purpose we designed a structure enabling optical injection of a controlled unequal number of negative electrons and positive holes into an isolated InGaAs quantum dot embedded in a GaAs matrix. Thereby, we(More)
The characteristics of an acceptor level in Sb-doped, p-type ZnO were studied using cathodoluminescence ͑CL͒ spectroscopy as a function of hole concentration. Variable-temperature CL measurements allowed us to estimate the activation energy of an Sb-related acceptor from temperature-induced decay of CL intensity. The values of activation energy of about(More)
We study optically single self-assembled quantum dots embedded within the wide quantum well of a mixed type quantum structure. We compare the steady state and pulsed photoluminescence spectra of these dots to those of previously studied " regular " dots. We unambiguously identify experimentally emission from various discrete charge state of the dots. We(More)
—Waveguide coupling to closed loop coupled-resonator optical waveguides is explored. By coupling a CROW chain back on itself, a reduction in individual resonant linewidth is achieved making these slow light modes more conducive to periodic filters toward novel frequency-comb integration. Through numerical simulation by finite-difference time-domain methods,(More)
ZnMgO thin films were grown by Molecular Beam Epitaxy on closely-lattice-matched MgO substrates with a Radio-Frequency (RF) generated oxygen plasma. The impact on the cubic ZnMgO of oxygen flow rate and applied RF power was investigated under a high vacuum condition (1E-6 Torr). Optical Emission Spectroscopy identified active species in the plasma including(More)