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Identifier 000459001
Title Advanced single -photon sources based on innovative semiconductor nanostructures
Alternative Title Προηγμένες μονοφωτονικές πηγές βασισμένες σε καινοτόμες ημιαγωγικές νανοδομές
Author Χατζαράκης, Νικόλαος
Thesis advisor Πελεκάνος, Νικόλαος
Reviewer Κοπιδάκης, Γεώργιος
Δελιγεώργης, Γεώργιος
Καφεσάκη, Μαρία
Κιοσέογλου, Γεώργιος
Ηλιόπουλος, Ελευθέριος
Δημάκης, Εμμανουήλ
Abstract In a rapidly evolving technological world, where quantum information processing will soon become a necessity, an ideal artificial quantum system that offers great potential in manipulating the electronic properties of matter, is the semiconductor quantum dot (QD). Quantum information processing and quantum computing developments depend crucially on the availability of efficient, controllable, and cost-effective sources of single and entangled photons. In this thesis, having in mind to develop practical QD-based single photon emitters, operating at non-cryogenic temperatures with enhanced characteristics, we have focused on self-assembled InAs/GaAs QDs grown by molecular beam epitaxy in the Stranski-Krastanov growth mode on (211)B GaAs substrates. This QD system combines all the benefits of (100) InAs/GaAs QDs with another important feature, which is the presence of a large piezoelectric (PZ) field along the growth axis of the QDs. One of the advantages that the PZ field offers is that the symmetry of the confinement potential is maintained inside the QD, leading to small fine-structure splittings, something essential for producing entangled photons. In addition, due to the PZ field, large exciton-biexciton splittings are generated, making this system suitable for high-temperature single photon applications. In our case, to achieve high-temperature operation, the InAs/GaAs QDs were incorporated in between GaAs/AlAs short-period superlattices. The resulting strong confinement of the carriers in the dots, drastically improved the temperature stability of the photoluminescence and allowed for single-photon emission at the elevated temperature of 230K. This is a high enough temperature, allowing for the first time, the noncryogenic operation of a single-photon emitter based on III-arsenide QDs. Furthermore, the multi-exciton lines of these strongly-confined InAs QDs have been thoroughly characterized. The observed redshifts of the biexciton and trion lines were attributed to the strong confinement and accompanying correlation effects. Our results suggest an attractive mechanism to tailor the transition energies of a single semiconductor QD by appropriate band-gap engineering of the surrounding barriers. It is important to note that this mechanism not only relates to the particular case of (211)B InAs QDs, but can be applied to any semiconductor QD system, including for instance the standard (100) InAs/GaAs QDs. An alternative way to make high-efficiency nano-emitters is the utilization of the plasmonic effect. Hybrid plasmonic nano-systems have been receiving great attention in the last 10-15 years, as they are able to provide significant enhancements in the optical properties of the nano emitters when they come in proximity of a metal. Although great progress has been made to understand how the plasmons interact with an emitter, there are still open questions and practical difficulties such as the control of the relative position of the nano emitter with respect to the metal, that require complex processing techniques. Here, the interaction between a nanowire emitter and a gold surface is experimentally studied as a function of their relative distance. Epitaxially grown GaAs/AlGaAs and GaAs/InAlAs core-shell nanowires are used as emitters, positioned on relatively flat gold surfaces of prepatterned templates. To controllably increase the emitter-metal distance, a Hafnia (HFO2) layer of varying thickness deposited by Atomic Layer Deposition, is used as spacer. A strong enhancement of the photoluminescence intensity (up to a factor of 40) is observed when the nanowire is lying directly on the metal surface, accompanied by a strong reduction of the carrier recombination lifetime by a factor of 2, that we interpret as due to the interaction between the nanowire emitter and surface plasmons. As prospective work of this thesis, we performed a quantum-confined Stark effect study on single CsPbBr3 nanocrystals. This nanocrystal system is particularly promising for cost-effective high-temperature nanophotonic applications, as these nanocrystals are chemically-synthesized and solution-processed, and exhibit excellent quantum yields (close to unity) and single photon emission at room temperature. In our study, we only observed tiny Stark shifts, suggesting that some very efficient screening mechanism exists in our nanocrystals. Finally, we demonstrated an alternative photon-collection scheme using half-ball lenses, increasing the collection efficiencies by a factor between 2 and 6, depending on the specifics of the emitter’s dielectric environment.
Language English
Subject Photon correlation
Συσχέτιση φωτονίων
Issue date 2023-11-29
Collection   School/Department--School of Sciences and Engineering--Department of Materials Science and Technology--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/9/f/1/metadata-dlib-1696574294-437180-13743.tkl Bookmark and Share
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