Scanning micro-photoluminescence studies of GaAs photonic crystals and perovskite structures

Thesis

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 FA_0.83Cs_0.17Pb(Br_xI_1-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.

Authors: Nuttall, L

• DOI: 10.5287/ora-1rr1epyz8
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Photonic crystals; FDTD simulations; Perovskite photovoltaics; Quantum optics