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UU5.09 - Top-Down Fabrication of GaAs Nanowire Antennas with Embedded Quantum Dots 
April 23, 2014   4:30pm - 4:45pm

Photonic nanowires operating as efficient single-mode waveguides are significant for applications such as light emitting devices, solar cells, and quantum light sources. While bottom-up fabrication of nanowires with embedded quantum emitters has been realized in several systems, in general the quality and purity of these emitters is less than ideal. Alternatively, top-down fabrication of nanowires around high quality self-assembled quantum dots can be realized but is technologically challenging. Here we demonstrate highly controlled plasma etching of GaAs nanowires with desired structural properties. Finite-difference time-domain simulations are used to achieve the optimal design, which includes a top-taper as a photon out-coupler and gold reflector below a layer of self-assembled InGaAs quantum dots. We perform high resolution photoluminescence spectroscopy, single photon correlation measurements, and time-resolved photoluminescence to characterize the properties of the QDs in the one-dimensional nanowires. We observe a huge enhancement in the light-extraction efficiency, > 60% from a single dot into the objective lens, compared to a dot in the bulk (~ 1%). Auto-correlation measurements are performed to confirm the high-quality single photon emission from the dots up to saturation excitation powers (corresponding to > 2 MHz APD counts after filtering). Using cross-correlation measurements between the different spectral lines, we clearly identify the neutral and charged excitons and bi-excitons from the same QD in the spectra. Finally, we characterize the effect of excitation power on the emission properties of the dots. At low excitation powers, we obtain spectral linewidths limited by the spectrometer resolution (~ 35 micro-eV). With increasing non-resonant excitation power, linewidth broadening and energy detuning of the spectral lines are observed. This behaviour is ascribed to filling surface states at the nanowire surface which create lateral electric fields. Based on the observed Stark shifts at high powers we can estimate the magnitude of the lateral electric fields. These results demonstrate the photonic nanowire is a highly efficient broad-band nano-antenna for high quality self-assembled quantum dots.

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Keynote Address
Panel Discussion - Different Approaches to Commercializing Materials Research
Business Challenges to Starting a Materials-Based Company
Fred Kavli Distinguished Lectureship in Nanoscience
Application of In-situ X-ray Absorption, Emission and Powder Diffraction Studies in Nanomaterials Research - From the Design of an In-situ Experiment to Data Analysis