Professor Robert Taylor

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.

Abstract:

Nanorod arrays were fabricated on a blue InGaN/GaN single quantum well (QW) LED wafer using nanoimprint lithography. A regular hexagonal lattice of nanorods was made at a pitch of 2 μm producing single quantum disks in the nanorods with diameter of ̃400 nm. Time integrated micro-photoluminescence was performed to investigate the emission properties of top down processed single nanorods at 4.2 K. Microphotoluminescence maps were made to study the spatial isolation of the photoluminescence emission, showing a good contrast ratio between nanorods. Excitation power dependent studies show screening of the quantum confined Stark effect for both the unprocessed wafer and the single nanorod. At low excitation powers, localised states appearing as sharp peaks in the photoluminescence spectrum were visible with a density of approximately four peaks per nanorod. © 2013 The Japan Society of Applied Physics.