The Design, Optimisation, and Characterisation of GaSb/GaAs Quantum Ring-Based Vertical-Cavity Devices Emitting at Telecoms Wavelengths.

Wilson, Tom and Hayne, Manus (2022) The Design, Optimisation, and Characterisation of GaSb/GaAs Quantum Ring-Based Vertical-Cavity Devices Emitting at Telecoms Wavelengths. PhD thesis, Lancaster University.

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Abstract

The aim of this work is to establish the feasibility of designing and producing telecoms wavelength vertical-cavity structures using GaSb quantum rings (QRs) embedded in GaAs - AlxGa1−xAs resonators. Additionally, various methods of characterising the optical and material properties of the produced samples are assessed, to determine the most suitable techniques in terms of accuracy, ease of use, cost, and measurement time. Extensive optical modelling is carried out to design and optimise vertical-cavity surface-emitting lasers (VCSELs), and single-photon light-emitting diodes (SPLEDs). Optical models are used to check sample growth quality, and provide sample selection criteria when used in conjunction with measured material parameters and optical transmission spectra. Various measurement techniques are compared for the quantification of AlxGa1−xAs in many-layered structures, including secondary-ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS), and electron energy-loss spectroscopy (EELS). SIMS proves to be effective for thick samples, particularly in terms of measurement speed and layer clarity, with XPS and EELS more suited for thinner samples, or where high resolution over a small area is required. Distributed Bragg reflectors (DBRs) grown at IQE using metalorganic vapour-phase epitaxy (MOVPE) are successfully combined with the QR active region and upper DBR overgrowth using molecular beam epitaxy (MBE) at Lancaster University. The graded IQE DBRs are shown to be very consistent their optical properties, and reduce the electrical resistance and growth time for the remainder of the optical device. SPLED devices are shown to emit light, operating around 1310nm and 1550 nm. At this time no single-photon emission was observed. VCSEL devices are shown to operate at around 1270 nm, demonstrating the telecoms-wavelength capabilities of the system, while device performance is limited by high resistance and other potential factors. Further improvements are discussed, including reducing device resistance, as well as processing the devices in the Lancaster Quantum Technology Centre cleanrooms.