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Title: Non-polar InGaN quantum dots : polarisation-controlled semiconductor single-photon sources at on-chip temperatures
Author: Wang, Tong
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2019
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Polarisation-controlled single-photon sources are at the heart of quantum information applications, e.g. truly secure communication with polarisation-based quantum key distribution protocols, and all-optical quantum computation with logic gates defined by the polarisation states of photons. Non-polar (1120) a-plane InGaN/GaN quantum dots are one of the strongest candidates due to their ability to operate at temperatures similar to those in on-chip conditions, and intrinsic polarisation properties built into the material. Time-integrated, time-resolved, polarisation-resolved micro-photoluminescence, and Hanbury Brown and Twiss studies are conducted on a-plane QDs fabricated by two different methods, yielding results that are not only a significant step forward in nitride-based single-photon research, but also open up the underexplored field of high-temperature semiconductor quantum dot photophysics. In particular, the first demonstration of ultrafast polarisation-controlled single-photon generation from a semiconductor quantum dot platform at 220K (-53 °C) is achieved, along with an unexpected observation of temperaturedependent fine-structure splitting previously unseen in other systems. Radiative recombination lifetime and slow-timescale spectral diffusion have been investigated with statistical significance, producing mean values that are on par with stateof- the-art nitride developments in the literature. Combined with efforts from theory collaborators, the insensitivity of radiative lifetime and optical polarisation to differences in the physical dimension, geometry and material composition of the quantum dots has been demonstrated. In particular, a-plane InGaN quantum dots have been shown both theoretically and experimentally to exhibit high polarisation degrees with deterministc axes along nitride crystal directions, from cryogenic to temperatures above 200 K. These developments advance the field of single-photon science and bring the current platform a step closer to on-chip quantum information applications. Meanwhile, other temperature-dependent optical properties, such as emission intensity quenching, exciton linewidth broadening and phonon-assisted redshift, have been investigated in detail. Parameters relevant to thermally assisted processes in the a-plane platform, including acoustic phonon scattering strengths, typical activation energies of local potential depths and Huang-Rhys factors, have also been evaluated for the first time, thereby facilitating further development of the platform and fundamental research of related photophysics.
Supervisor: Taylor, Robert Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available