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Abstract:

We report on optical studies of non-polar InGaN quantum dots grown on the (11$ \bar 2 $2) plane. Excitonic and biexcitonic complexes are identified by their power dependence and show similar binding energies (∼ 36 meV) and recombination dynamics to conventional polar (0001) InGaN quantum dots. Measured lifetimes as low as 300 ps suggest a reduced internal electric field when compared with polar InGaN quantum dots. Temperature dependent micro-photoluminescence measurements on a single exciton with a lifetime of 327ps reveal no significant exciton linewidth broadening up to 120K, suggesting a reduction in phonon coupling strength when compared to polar quantum dots. This is supported by a measured lifetime of 313 ps for this exciton at 77 K, suggesting the measured exciton decay is almost purely radiative. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

InGaN quantum dot (QD) structures have been grown by metal organic vapour phase epitaxy (MOVPE) on non-polar (11-20) GaN surfaces by employing an anneal step in nitrogen immediately after the growth of the InGaN. Here, we compare the growth of such structures on pseudo-substrates grown using an epitaxial lateral overgrowth (ELOG) technique and on pseudo-substrates grown using a simpler in situ SiNx interlayer. The less complex defect reduction approach results in a significantly higher defect density, but does not detrimentally effect the QD formation. For both types of pseudo-substrate, sharp peaks with resolution limited widths are observed in both cathodoluminescence at 9 K and micro-photoluminescence at 4.2 K. The QDs demonstrate significantly reduced exciton lifetimes compared to structures grown on c-plane, which has advantages for possible applications in single photon sources. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

We observe excited exciton and biexciton states of localised excitons in an anisotropic quantum ring, where large polarisation asymmetry supports the presence of a crescent-like localised structure. We also find that saturation of the localised ground state exciton with increasing excitation can be attributed to relatively fast dissociation of biexcitons (∼430 ps) compared to slow relaxation from the excited state to the ground state (∼1000 ps). As no significant excitonic Aharonov-Bohm oscillations occur up to 14 T, we conclude that phase coherence around the rim is inhibited as a consequence of height anisotropy in the quantum ring. © 2013 AIP Publishing LLC.

Abstract:

We report on optical characterization of self-assembled InGaN quantum dots (QDs) grown on three GaN pseudo-substrates with differing threading dislocation densities. QD density is estimated via microphotoluminscence on a masked sample patterned with circular apertures, and appears to increase with dislocation density. A non-linear excitation technique is used to observe the sharp spectral lines characteristic of QD emission. Temporal variations of the wavelength of emission from single QDs are observed and attributed to spectral diffusion. The magnitude of these temporal variations is seen to increase with dislocation density, suggesting locally fluctuating electric fields due to charges captured by dislocations are responsible for the spectral diffusion in this system. © 2013 The Japan Society of Applied Physics.