Controlling the charge environment of single quantum dots in a photonic-crystal cavity

We demonstrate that the presence of charge around a semiconductor quantum dot (QD) strongly affects its optical properties and produces non-resonant coupling to the modes of a microcavity. We first show that, besides (multi)exciton lines, a QD generates a spectrally broad emission which efficiently couples to cavity modes. Its temporal dynamics shows that it is related to the Coulomb interaction between the QD (multi)excitons and carriers in the adjacent wetting layer. This mechanism can be suppressed by the application of an electric field, making the QD closer to an ideal two-level system.Comment: 12 pages, 4 figure

Enhanced spontaneous emission in a photonic crystal light-emitting diode

We report direct evidence of enhanced spontaneous emission in a photonic crystal (PhC) light-emitting diode. The device consists of p-i-n heterojunction embedded in a suspended membrane, comprising a layer of self-assembled quantum dots. Current is injected laterally from the periphery to the center of the PhC. A well-isolated emission peak at 1300nm from the PhC cavity mode is observed, and the enhancement of the spontaneous emission rate is clearly evidenced by time-resolved electroluminescence measurements, showing that our diode switches off in a time shorter than the bulk radiative and nonradiative lifetimesComment: 10 page

Picosecond Time-Resolved Cathodoluminescence to Probe Exciton Dynamics in α-Plane (Al,Ga)N/GaN Quantum Wells

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7-August 11, 201

Implications from dimensionless parameter scaling experiments

The dimensionless parameter scaling approach is increasingly useful for predicting future tokamak performance and guiding theoretical models of energy transport. Experiments to determine the {rho}* (gyroradius normalized to plasma size) scaling have been carried out in many regimes. The electron {rho}* scaling is always ``gyro-Bohm``, while the ion {rho}* scaling varied with regime. The ion variation is correlated with both density scale length (L mode, H mode) and current profile. The ion {rho}* scaling in the low-q, H-mode regime is gyro-Bohm, which is the most favorable confinement scaling observed. New experiments in {beta} scaling and collisionality scaling have been carried out in low-q discharges in both L mode and H mode. In L mode, global analysis shows that there is a slightly unfavorable {beta} dependence ({beta}{sup {minus}0.1}) and no {nu}* dependence. In H-mode, global analysis finds a weak {beta} dependence ({beta}{sup 0.1}) and an unfavorable dependence on {nu}*. The lack of significant {beta} scaling spans the range of {beta}{sub N} from 0.25 to 2.0. The very small {beta} dependence in L mode and H mode is in contradiction with the standard global scaling relations. This contradiction in H mode may be indicative of the impact on the H-mode database of low-n tearing instabilities which are observed at slightly higher {beta}{sub N} in the {beta} scaling experiments. The measured {beta} and {nu}* scalings explain the weak density dependence observed in engineering parameter scans. It also points to the power of the dimensionless parameter approach, since it is possible to obtain a definitive size scaling from experiments on a single tokamak