Optical fabrication and characterisation of SU-8 disk photonic waveguide heterostructure cavities

In order to demonstrate cavity quantum electrodynamics using photonic crystal (PhC) cavities fabricated around self-assembled quantum dots (QDs), reliable spectral and spatial overlap between the cavity mode and the quantum dot is required. We present a method for using photoresist to optically fabricate heterostructure cavities in a PhC waveguide with a combined photolithography and micro-photoluminescence spectroscopy system. The system can identify single QDs with a spatial precision of ±25 nm, and we confirm the creation of high quality factor cavity modes deterministically placed with the same spatial precision. This method offers a promising route towards bright, on-chip single photon sources for quantum information applications

Non-polar InGaN quantum dot emission with crystal-axis oriented linear polarization

Polarization sensitive photoluminescence is performed on single non-polar InGaN quantum dots. The studied InGaN quantum dots are found to have linearly polarized emission with a common polarization direction defined by the [0001] crystal axis. Around half of ∼40 studied dots have a polarization degree of 1. For those lines with a polarization degree less than 1, we can resolve fine structure splittings between −800 μeV and +800 μeV, with no clear correlation between fine structure splitting and emission energy.This research was supported by the Engineering and Physical Sciences Research Council (EPSRC) UK (Grant No. EP/H047816/1).This is the accepted manuscript of a paper published in Applied Physics Letters (Reid BPL, Kocher C, Zhu T, Oehler F, Chan CCS, Oliver RA, Taylor RA, Applied Physics Letters, 2015, 106, 171108, doi:10.1063/1.4919656). The final version is available at http://dx.doi.org/10.1063/1.491965

Observations of Rabi oscillations in a non-polar InGaN quantum dot

Experimental observation of Rabi rotations between an exciton excited state and the crystal ground state in a single non-polar InGaN quantum dot is presented. The exciton excited state energy is determined by photoluminescence excitation spectroscopy using two-photon excitation from a pulsed laser. The population of the exciton excited state is seen to undergo power dependent damped Rabi oscillations.This research was supported by the Engineering and Physical Sciences Research Council (EPSRC) U.K. (Grant No. EP/H047816/1).This version is the author accepted manuscript. The published version can also be found on the publisher's website at: http://scitation.aip.org/content/aip/journal/apl/104/26/10.1063/1.4886961 © 2014 AIP Publishing LL

Growth of non-polar (11-20) InGaN quantum dots by metal organic vapour phase epitaxy using a two temperature method

Non-polar (11-20) InGaN quantum dots (QDs) were grown by metal organic vapour phase epitaxy. An InGaN epilayer was grown and subjected to a temperature ramp in a nitrogen and ammonia environment before the growth of the GaN capping layer. Uncapped structures with and without the temperature ramp were grown for reference and imaged by atomic force microscopy. Micro-photoluminescence studies reveal the presence of resolution limited peaks with a linewidth of less than ∼500 μeV at 4.2 K. This linewidth is significantly narrower than that of non-polar InGaN quantum dots grown by alternate methods and may be indicative of reduced spectral diffusion. Time resolved photoluminescence studies reveal a mono-exponential exciton decay with a lifetime of 533 ps at 2.70 eV. The excitonic lifetime is more than an order of magnitude shorter than that for previously studied polar quantum dots and suggests the suppression of the internal electric field. Cathodoluminescence studies show the spatial distribution of the quantum dots and resolution limited spectral peaks at 18 K.This work was funded by the EPSRC (Grant Nos. EP/J003603/1 and EP/H047816/1).This is the final published version. It first appeared at http://scitation.aip.org/content/aip/journal/aplmater/2/12/10.1063/1.4904068

Nitride Single Photon Sources

Single photon sources are a key enabling technology for quantum communications, and in the future more advanced quantum light sources may underpin other quantum information processing paradigms such as linear optical quantum computation. In considering possible practical implementations of future quantum technologies, the nitride materials system is attractive since nitride quantum dots (QDs) achieve single photon emission at easily accessible temperatures [1], potentially enabling the implementation of quantum key distribution paradigms in contexts where cryogenic cooling is impracticable

Quantum dot-like excitonic behavior in individual single walled-carbon nanotubes.

Semiconducting single-walled carbon nanotubes are one-dimensional materials with great prospects for applications such as optoelectronic and quantum information devices. Yet, their optical performance is hindered by low fluorescent yield. Highly mobile excitons interacting with quenching sites are attributed to be one of the main non-radiative decay mechanisms that shortens the exciton lifetime. In this paper we report on time-integrated photoluminescence measurements on individual polymer wrapped semiconducting carbon nanotubes. An ultra narrow linewidth we observed demonstrates intrinsic exciton dynamics. Furthermore, we identify a state filling effect in individual carbon nanotubes at cryogenic temperatures as previously observed in quantum dots. We propose that each of the CNTs is segmented into a chain of zero-dimensional states confined by a varying local potential along the CNT, determined by local environmental factors such as the amount of polymer wrapping. Spectral diffusion is also observed, which is consistent with the tunneling of excitons between these confined states

Observations of Rabi oscillations in a non-polar InGaN quantum dot

Experimental observation of Rabi rotations between an exciton excited state and the crystal ground state in a single non-polar InGaN quantum dot is presented. The exciton excited state energy is determined by photoluminescence excitation spectroscopy using two-photon excitation from a pulsed laser. The population of the exciton excited state is seen to undergo power dependent damped Rabi oscillations.This research was supported by the Engineering and Physical Sciences Research Council (EPSRC) U.K. (Grant No. EP/H047816/1).This version is the author accepted manuscript. The published version can also be found on the publisher's website at: http://scitation.aip.org/content/aip/journal/apl/104/26/10.1063/1.4886961 © 2014 AIP Publishing LL

Carrier trapping and confinement in Ge nanocrystals surrounded by Ge3N4

We investigated the optical properties of Ge nanocrystals surrounded by Ge3N4. The broad emission ranging from infrared to blue is due to the dependence on the crystal size and preparation methods. Here, we report high resolution Photoluminescence (PL) attributed to emission from individual Ge nanocrystals (nc-Ge) spatially resolved using micro-photoluminescence and detailed using temperature and power-dependent photoluminescence studies. The measured peaks are shown to behave with excitonic characteristics and we argue that the spread of the nc-Ge peaks in the PL spectrum is due to different confinement energies arising from the variation in size of the nanocrystals

Origins of Spectral Diffusion in the Micro-Photoluminescence of Single InGaN Quantum Dots

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

Optical studies of the surface effects from the luminescence of single GaN/InGaN nanorod light emitting diodes fabricated on a wafer scale

Time-resolved and time-integrated microphotoluminescence studies at 4.2 K were performed on a single InGaN/GaN nanorod light emitting diode, fabricated in an array, on a wafer scale by nanoimprint lithography. Emission properties and carrier dynamics of the single nanorods are presented. Sharp peaks of 2 meV line-width were observed. The single nanorods possess longer decay rates than an unprocessed wafer at delay-times above 50 ns after excitation. The time evolution of the photoluminescence spectra implies that the slower decay times are due to surface related localisation near the perimeter of the nanorods, resulting in a spatial separation of the recombining carriers at low excitation densities. © 2013 American Institute of Physics