Simulation and manufacture of gallium nitride integrated photonics.

Maynard, Cobi 2024. Simulation and manufacture of gallium nitride integrated photonics. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis presents the simulation and fabrication of gallium nitride (GaN) integrated photonic devices for use at a wavelength of 1550 nm. We have developed fabrication processes for GaN on sapphire ridge waveguides, using e-beam lithography, nickel lift-off, and inductively-coupled plasma (ICP) reactive ion etching (RIE). The simulation of waveguides allowed for the determination of waveguide widths and thicknesses for which optical modes are supported, and to identify geometries for which higher order modes are supported, as well as an investigation into the effects a non-vertical etch profile has on the waveguide modes. Nanobeams of GaN with an equilateral triangular cross-section were simulated and found to support waveguide modes at a wavelength of 1550 nm, with a lateral width greater than 400 nm required for optical confinement. Confined waveguide modes were found for both orthogonal TE and TM polarisations to be degenerate in effective index. This degeneracy was lifted and waveguides became birefringent when the simulated etch angle was increased or decreased, and when the waveguide had varying degrees of asymmetry introduced, showing insight into how asymmetry and etch angle affects a waveguide mode in a triangular waveguide, which are important when considering fabrication tolerances. We have discussed the results of three-dimensional simulations of GaN photonic crystal nanobeam cavities (PCNCs), where we use Distributed Bragg Reflectors (DBRs) as mirrors in the cavity, calculating the mirror strength as a function of filling fraction using the spatial electric field profile. We compare and contrast two methods of calculating cavity Q factor, determining the ringdown method to be more accurate and appropriate than the spectral method for the simulations considered. A method of analysing the effect of loss on Q is presented using the imaginary refractive index of the device, finding that Q decreases exponentially with imaginary index.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Physics and Astronomy
Subjects:	Q Science > QC Physics
Uncontrolled Keywords:	semiconductor, semiconductor manufacturing, semiconductor fabrication, compound semiconductor, compound semiconductor manufacturing, compound semiconductor fabrication, photonics, integrated photonics, photonic integrated circuits. gallium nitride, GaN, GaN integrated photonics, GaN integrated photonics manufacturing, GaN integrated photonics fabrication, integrated photonics manufacturing, integrated photonics fabrication, waveguide, waveguides, waveguide fabrication, waveguide manufacturing, optical cavity, triangular waveguide, simulation, lithography
Funders:	Engineering & Physical Sciences Research Council
Date of First Compliant Deposit:	22 May 2025
Last Modified:	22 May 2025 15:14
URI:	https://orca.cardiff.ac.uk/id/eprint/178418

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