Thesis
Development and exploitation of additive GaN micro-lenses for applications in quantum technology and micro-optics
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2024
- Thesis identifier
- T16830
- Person Identifier (Local)
- 201969414
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Shaping the nanoworld has been a desire of physicists and engineers since Richard Feynman’s famous talk ‘Plenty of room at the bottom’ in 1959. It’s the gift of great visionaries to articulate and maybe even shape the Zeitgeist. Today, a vast set of tools is available to both explore and manipulate matter on the micro- and nanometer scale, offering an unprecedented and fruitful interaction between humans and base matter. This thesis is an incremental part of the overall effort to harness the unique properties of the micro- and nanocosmos for the benefit of humanity. The field of visible optics is particularly interesting because in many atoms, molecules and materials valence electrons can couple to photons in the visible, near infra red or ultra violet parts of the electromagnetic spectrum. Light-matter interaction of this kind allows to connect remotely to the close-ranged interaction between those electrons and the atom core, other electron shells or maybe neighboring atoms in a crystal, because photons can travel vast distances in a relatively undisturbed state. A great example of harnessing electron-photon coupling in semiconductor crystals are UV-green light emitting gallium nitride diodes, which are widely used in lighting applications in our homes, cars and outdoor spaces today. Here electrons and holes are pumped into a heterogeneously doped semiconductor junction and recombine to produce light emission close to the band gap of the semiconductor material which is set by interaction of the atoms in the crystal. This blue and reasonably broad light emission is then coupled to phosphorescent material, converting some of the photons to lower wavelength and generating a white light impression after absorption by our retinas and signal processing performed by the neural tissue. Gem stones have fascinated humans for millennia, probably due to their bright and radiant colours, their hardness and the potential to cut them into beautifully precise geometric shapes. Today we have learned that we can explain many of their properties with the quantum mechanical description of light-matter interaction. Particularly their bright colours can often be caused by well-defined inclusions of foreign atoms into the crystal’s lattice. These artificial atoms are well protected from the environment and as they are optically active we can use photons to investigate their inner state. At the heart of many today’s efforts in the space of quantum technology like quantum sensing and quantum computing lays the idea to engineer the photon-gated interaction with the inner workings of matter to expand our ability to shape the world around us. Micro-optical elements can facilitate efficient coupling between photons and fermionic matter. Commercialization has long reached this technology in many forms, for instance micro-lens arrays made of glass or polymer materials are used to focus light on the limited area of semiconductor light detectors, just to name one application. This thesis mainly explores the use of GaN micro-lenses for enhancing the interaction with a specific defect emitter in diamond - the nitrogen vacancy centre - in the context of transfer printing, an integration method that allows flexible combination of different preprocessed and highly specialized semiconductor devices. This method relies on careful preparation of free-standing semiconductor thin films on donor chips, and highly engineered surfaces on the receiving semiconductor chips. Transfer printing harnesses the visco-elastic properties of the polymer polydimethylsiloxane, which is used in a similar manner to carved potato stamps that children dip into ink to create colourful geometric shapes, relying on white light microscopy in combination with nanoscale precision 6-axis alignment stages. The thesis summaries both the micro-fabrication process development of GaN micro-lenses in comparison to monolithic diamond lenses as well as the integration of the GaN micro-lenses with planar and preprocessed diamond surfaces. In particular, the potential for enhanced light coupling efficiency to the nitrogen vacancy centre is investigated in three different scenarios: Laser written nitrogen vacancy centre doublets, NV clusters with < 1_m proximity to a planar diamond interface, as well as commercially available diamond probes for scanning magnetometer with a single NV centre. To properly assess the properties of the assembled micro-scale systems, a single-photon sensitive confocal microscope is built to probe the fluorescence response from nitrogen vacancy centres. In summary it is found by both simulations and experiments that transfer printed GaN micro-lenses can effectively enhance the light-matter coupling in most of the studied cases. Other interesting and developing fields with much technological overlap are fibre optics, integrated photonic circuits and nano-scale laser sources. Printing of GaN micro-lenses on a fibre and integrated waveguide facet as well as in a 3D geometry above an optically pumped nanowire lasers is demonstrated and potential benefits are studied both experimentally and by finite difference time domain simulations. Here we mostly find marginal or limited utility for the targeted applications, but these efforts show effectively how flexible transfer printing can be as an integration method, pushing the forefront of this specialized knowledge space.
- Advisor / supervisor
- Strain, Michael
- Dawson, Martin
- Resource Type
- Note
- This thesis was previously held under moratorium from 19th February 2024 until 19th February 2026.
- DOI
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