Advanced processing strategies for site-controlled pyramidal quantum dots

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Varo, Simone
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University College Cork
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Today, the world is on the verge of a new technological breakthrough that has been called the “second quantum revolution”: much like the understanding of semiconductor physics paved the way for the development of integrated circuits and ushered the age of information technology, the development of the first working quantum computers might start a profound change in the way we process information, and pave the way for much anticipated technological breakthrough. In my thesis, I have investigated the applications of Pyramidal Quantum Dots (PQDs) as potential sources of single and entangled photons, with a particular focus on improving their quality and brightness, and explored new approaches for their processing that would make them suitable for integration in future quantum devices. In order to address the limits of the conventional InGaAs in GaAs PQDs in relation to resonant pumping of the biexcitonic state, I contributed to the development of two new families of dots: GaAs in AlGaAs PQDs and GaAs dots confined by superlattice barriers. For the former, only results of growths on templates of smaller size were reported in the literature, while the latter is a completely new family of PQDs altogether. Results reported in this thesis indicate a surprising uniformity in spectral features for either family, and demonstrate that resonant excitation can indeed be achieved due to the binding biexcitonic state. In collaboration with Prof. Di Falco’s group in the University of St. Andrews (UK), we have demonstrated potential applications in the field of semiconductor non-classical light sources of the Electron Beam Induced Deposition technique, which allowed us to fabricate complex dielectric nanostructures directly above the quantum emitters. Our work showed how this approach doesn’t cause any significant degradation in the emission spectra, and was complemented by a large number of simulations to elucidate the underlying mechanisms that allow SiO_2 nanostructures to boost light extraction efficiency form the semiconductor matrix depending on their shape. A more promising approach to boost the brightness of our dots was also developed, in the form of a self-aligning technique that allows to fabricate micro and nanopillars using dry etching, and that allowed us to achieve our own record of brightness. Furthermore, an approach to compensate for the effects of the excitonic fine structure splitting on the level of entanglement was devised: the model we have developed complements similar proposals that have previously appeared in the literature, but is also extremely intuitive due to its sequential logic gate structure. Finally, for the first time transmission electron microscopy of PQDs was achieved in a joint effort with Queen’s University Belfast, a success in large part made possible by the new processing strategies devised in this thesis, and whose preliminary results are here reported.
Quantum optics , Quantum dots , Semiconductor processing and fabrication , Photonics
Varo, S. 2021. Advanced processing strategies for site-controlled pyramidal quantum dots. PhD Thesis, University College Cork.