Final PhD Oral Examination (Thesis Title: “Luminescent Properties Of Pb-Based (PbX) Colloidal Quantum Dots (CQDs) In Vacuum, On Silicon And Integrated With A Silicon-On-Insulator (SOI) Photonic Integrated Circuit (PIC)”)

Event Date and Time: 
Thu, 2016-03-17 12:30 - 14:30
Room 203, Graduate Student Centre
Local Contact: 
Physics and Astronomy, UBC
Intended Audience: 

In the rapidly evolving field of experimental quantum information processing, one important sub-field pursues a potentially scalable implementation that transports quantum information encoded in photons throughout ``photonic circuits'' fabricated in a silicon wafer. A key component is an efficient on-demand source of these single photons, and this dissertation aimed to assess the feasibility of one proposed realization of such a source by integrating few PbSe colloidal quantum dots (CQDs, demonstrated single photon emitters in nanoparticle form) into the mode volume of an optical microcavity designed to efficiently direct quantum dot emission into a silicon photonic circuit. Although no direct evidence of single photon emission was observed, results prompted a number of follow-up experiments and considerable theoretical modeling to understand this quantum dot, photonic circuit system.

The methods of investigation included (1) temporally-, spectrally-, and spatially-resolved photoluminescence (PL) measurements of PbSe CQDs integrated into SOI PICs and relatable environments (solution, thick film, thin film), (2) temperature-dependent, air-exposure studies of PbSe CQD thick film PL, (3) development and application of kinetic and quantum mechanical cavity-coupled modeling that admit complete accounting of the photonic density of states, depolarization effects, and non-radiative decay, and (4) a photon coincidence test of single photon emission.

The main findings of this work are: (1) while capture of cavity-enhanced PbSe CQD emission into a silicon photonic circuit was demonstrated, the overall photon generate rate is inadequate for any useful implementation, (2) the measured coupling rate can be modeled and explained in terms of system parameters extracted from auxiliary experimental results obtained with the PbSe CQDs in isolation, or on isolated microcavities, and (3) consistent results could only be obtained after nontrivial depolarization factors and non-radiative decay processes are properly accounted for. From this it is clear that the performance of PbSe CQDs in this configuration of a single photon source in silicon is currently limited by a long-lived trap state with a several microsecond lifetime, and large depolarization effects that inhibit emission. Although plausible future efforts may mitigate these effects substantially, performance may still be hindered by the intrinsic emission strength of PbSe CQDs.

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