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Title: Microscopy and spectroscopy of materials for blue single photon sources
Author: Springbett, Helen Phoebe
ISNI:       0000 0004 7961 8099
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Semiconductor quantum dots (QDs) have shown much interest in recent years as potential single photon emitters. The InGaN-GaN system in particular offers comparably high temperature emission, polarised emission, and access to the green and blue regions. This has the advantages of completing the visible spectrum, and being the region in which ultrafast single photon detectors display the greatest sensitivity. This thesis uses microscopy techniques to investigate the methods by which such QDs can be grown and incorporated into device structures, and finally measures the single photon emission via photoluminescence spectroscopy. This study investigates two methods by which self-assembled quantum dots can be grown: modified droplet epitaxy and via growth of InGaN islands. It is hoped that gaining a deeper understanding of the growth processes and structural evolution upon capping will allow us to have greater control over dot size, geometry and density during growth. Furthermore, it presents a study on the incorporation of these dots in recently developed mesoporous distributed Bragg reflectors, which boast perfect lattice matching and a facile fabrication method. Microscopy analysis provides insight into the method of etching along dislocation channels, and the changing morphology of the layer stack. Furthermore, it provides insight into the etching of the QD layer itself. Spectroscopy analysis was thus performed to ascertain the effect of porosification on the emission properties. This study provides the first evidence of a working quantum porous device in the GaN system, and reports single photon emission with a g⁽²⁾(0) value of 0.126 ± 0.003 through optimisation of excitation conditions. Furthermore, a recorded value for the fast timescale spectral diffusion much longer than the radiative lifetime of a dot provides a promising step towards the realisation of indistinguishable single photons.
Supervisor: Oliver, Rachel Angharad Sponsor: EPSRC ; JSPS
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: quantum dots ; gallium nitride ; semiconductor ; single photon sources ; photon ; microscopy ; electron microscopy ; spectroscopy