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We report on excitonic single photon emission and biexcitonic photon bunching from an InGaN quantum dot formed on the apex of a hexagonal GaN micropyramid. An approach to suppress uncorrelated emission from the pyramid base is proposed, a metal lm is demonstrated to eectively screen background emission and thereby signicantly enhance the signal-to-background ratio of the quantum dot emission. As a result, the second order coherence function at zero time delay g(2)(0) is signicantly reduced (to g(2)(0) = 0.24, raw value) for the excitonic autocorrelation at a temperature of 12 K under continuous wave excitation, and a dominating single photon emission is demonstrated to survive up to 50 K. The deterioration of the g(2)(0)-value at elevated temperatures is well understood as the combined eect of reduced signal-to-background ratio and limited time resolution of the setup. This result underlines the great potential of site controlled pyramidal dots as sources of fast polarized single photons.

We report on the observation of linearly polarized single photon antibunching in the excitonic emission from a site-controlled InGaN quantum dot. The measured second order coherence function exhibits a significant dip at zero time difference, corresponding to g(m)(2) (0) = 0: 90 under continuous laser excitation. This relatively high value of g(m)(2) (0) is well understood by a model as the combination of short exciton life time (320 ps), limited experimental timing resolution and the presence of an uncorrelated broadband background emission from the sample. Our result provides the first rigorous evidence of InGaN quantum dot formation on hexagonal GaN pyramids, and it highlights a great potential in these dots as fast polarized single photon emitters if the background emission can be eliminated., Funding Agencies|Carl Trygger Foundation for Scientific Research; Swedish Research Council (VR); Nano-N consortium - Swedish Foundation for Strategic Research (SSF); Knut and Alice Wallenberg Foundation; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Font-D, at Linkoping University

The influence of the source gas supply sequence prior to growth and the NH3 input partial pressure (PoNH3) on the nucleation of InN islands during the initial stages of hydride vapor phase epitaxy on a nitrided (0001) sapphire substrate was investigated. The crystalline quality of the InN layer after subsequent lateral growth was also examined. When NH3 was flowed prior to growth, single-crystal hexagonal InN islands formed. When InN was grown with a higher PoNH3, the number of InN islands decreased remarkably while their diameter increased. The crystalline quality of InN grown on the hexagonal islands with a high PoNH3 significantly improved with increasing growth time. A strong PL spectrum was observed only from InN layers grown with a high PoNH3. It was thus revealed that an NH3 preflow and a high PoNH3 are effective for producing InN with high crystalline quality and good optical and electrical properties., Funding Agencies|Japan Society for the Promotion Science|23760006|International Training Program||Japan Society for the Promotion of Science

The emission of a charged exciton in an InGaN quantum dot (QD) on top of a GaN pyramid is identified experimentally. The intensity of the charged exciton exhibits the expected competition with that of the single exciton, as observed in temperature-dependent micro-photoluminescence measurements, performed with different excitation energies. The non-zero charge state of this complex is further supported by time resolved micro-photoluminescence measurements, which excludes neutral alternatives of biexciton. The potential fluctuations in the vicinity of the QD that localizes the charge carriers are proposed to be responsible for the unequal supply of electrons and holes into the QD., Funding Agencies|NANO-N consortium||Swedish Foundation for Strategic Research (SSF)

The coupling between longitudinal-optical (LO) phonons and neutral excitons in two different kinds of InGaAs pyramidal quantum dots embedded in either AlGaAs or GaAs barriers is experimentally examined. We find a slightly weaker exciton-LO-phonon coupling and increased linewidth of the phonon replicas for the quantum dots with GaAs barriers compared to the ones with AlGaAs barriers. These results, combined with the fact that the LO-phonon energy of the exciton is the same for both kinds of dots, are taken as evidence that the excitons mainly couple to LO-phonons within the QDs., Original Publication:Daniel Dufåker, L. O. Mereni, Fredrik K. Karlsson, V. Dimastrodonato, G. Juska, Per-Olof Holtz and E. Pelucchi, Exciton-phonon coupling in single quantum dots with different barriers, 2011, Applied Physics Letters, (98), 25, 251911.http://dx.doi.org/10.1063/1.3600781Copyright: American Institute of Physicshttp://www.aip.org