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Title: Scanning micro-photoluminescence studies of GaAs photonic crystals and perovskite structures
Author: Nuttall, Luke
ISNI:       0000 0004 7966 4212
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2019
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The first part of this thesis focuses on a novel design of photonic crystal microcavity coupled to InGaAs quantum dots. Such coupled dot-cavity systems can be used as enhanced single photon sources for quantum information applications and more complicated arrangements could even be used as optical switches in a quantum computer. A photolithography process is used to fabricate these cavities, allowing them to overcome many of the difficulties involved in achieving reliable dot-cavity coupling in traditional e-beam defined cavities. Theoretical FDTD simulations are used to predict the Q factor and mode volume (1.44 (λ0/n)3) of this cavity design. The fabrication process is given in detail, and micro-photoluminescence measurements are used to verify successful cavity fabrication. A success rate of 85% is achieved with Q factors as high as 7.4 × 103 at a wavelength of around 1.25 µm. These cavities are shown to have comparable performance to existing designs such as L3 and Notomi cavities fabricated using e-beam lithography. The second part covers studies of four different polycrystalline perovskite films with compositions of the form FA0.83Cs0.17Pb(BrxI1-x)3 and varying bromine fraction x ∈ {0.1, 0.2, 0.3, 0.4}. These perovskites are promising candidates for commercially scalable photovoltaic applications and have received a great deal of scientific interest over the past decade. This particular composition has been shown to have improved stability and optoelectronic properties compared to other perovskites. Micro-photoluminescence mapping is used to study the temperature dependence and structure of these samples. The diffusion lengths are found to be in the range from 2 µm to 5 µm, and evidence of photon recycling over longer distances is identified. Time-resolved photoluminescence measurements are carried out at cryogenic temperatures to study the carrier decay dynamics. A theoretical model of the decay process is developed and fitted to the data. Both excitons and free carriers are found to contribute to the emission, with the 10% bromine sample having the highest exciton binding energy.
Supervisor: Taylor, Robert Sponsor: Engineering and Physical Sciences Research Council ; Hitachi Cambridge Laboratory
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Quantum optics ; Photonic crystals ; FDTD simulations ; Perovskite photovoltaics