Departmental 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))

Speaker: 
CHARLES FOELL III
Event Date and Time: 
Mon, 2016-01-18 09:00 - 12:00
Location: 
Henn 309
Local Contact: 
Physics and Astronomy, UBC
Intended Audience: 
Public

ABSTRACT:
On-demand single photon sources have advanced disciplines including metrology, biotechnology, photonics, sensing, medical physics, meteorology and spectroscopy.  Another is linear optical quantum information processing (LOQIP), whose projected applications include communication, simulation, and computing with functionality believed to be far beyond what is achievable without explicit utilization of quantum physics.

Key LOQIP aims require multitudes of single photon sources, practically realizable only if these sources and accompanying photon detectors, electronics, and linear optical elements are scalably miniaturized and embedded in a host platform.  Of the candidate host platforms for LOQIP, silicon-on-insulator (SOI) already admits scalably miniaturized optics and electronics in the form of integrated photonic circuits and integrated electronic circuits.  However, inadequate on-demand single photon sources in the SOI platform impedes LOQIP, let alone other applications.

This dissertation contains experiments and modeling that seek to answer if, and how, colloidal quantum dots (CQDs) may be employed as on-demand photon sources for LOQIP in the SOI platform.  Included are rigorous evaluations of key CQD properties in a SOI photonic environment obtained through: (1) development and application of a kinetic model of CQD thick film integrated photoluminescence, across both in-house and in-literature samples, particularly with regard to the effects of air exposure, and (2) quantum mechanical modeling of power-dependent, silicon photonic crystal cavity-coupled CQD photoluminescence, with detailed dielectric modeling of the CQDs in the photonic crystal cavity.  Also included are in-house studies on the time-resolved emission of various CQD formulations, from in-solution to thick film to thin film, and demonstration of cavity-enhanced CQD PL into a SOI photonic circuit.

Findings are (1) the emission behavior of PbSe CQDs in silicon photonic circuits and related environments is consistently modeled so long as depolarization factors and non-radiative decay are properly accounted for.  (2) The emission rate of a PbSe CQD into a silicon photonic crystal cavity mode is a factor of 2 greater than the sum of decay into all other radiative modes, but exciton relaxation is dominated by non-radiative decay.  (3) The performance of PbSe CQDs for single photon source applications are limited by a long-lived trap state with a several microsecond lifetime, and large depolarization effects that inhibit emission.

 

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