Exploring MBE Growth Of Quantum Dots: Low Density Growth For Quantum Information Devices.

This thesis concerns the growth and subsequent application of InAs/GaAs quantum dots for novel research applications including entangled photon sources, and coupled quantum well/quantum dot devices. This thesis gives an overview of quantum dot growth and tunable parameters of quantum dots (QDs), showing a review of prior work detailing their composition and properties. Special attention is given to wavelength tuning, and optimisation of the linewidth for a target application, including analysis of post-growth annealing. Subsequent discussion focuses on low-density quantum dot samples, both in terms of growth and application. In conjunction with Cambridge University, micro-photoluminescence results of a short-wavelength QD sample are demonstrated, showing successful use of the rotation stop growth method, with further analysis and comparisons made with photoluminescence maps and atomic force microscopy. Analysis of long- wavelength (>1300nm at room temperature) QDs is also shown, with single dot work being performed on rotation-stop growth samples in analysis of Fine Structure Splitting (FSS) of individual QDs by Heriot Watt University. Results show an unexpectedly low FSS value for samples grown at the University of Sheffield, with potential for long wavelength entangled photon emitters. Growth optimisation of both the long- and short-wavelength structures is described, with optimisation required for the longer-wavelength samples, due to a comparative lack of cross-wafer QD density variation. A novel adjustment to photoluminescence excitation is also discussed, with polarisation analysis being performed on QD samples designed for optical emission. Results indicate that QD properties have little to no effect on the spin retention in GaAs-capped QDs: instead surrounding material has a larger effect, indicating that spin loss happens primarily between excitation and capture