Design of semimetal electronics relying on the quantum confinement effect

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dc.availability.bitstreamcontrolled
dc.contributor.advisorFahy, Stephen B.en
dc.contributor.advisorAnsari, Lidaen
dc.contributor.advisorexternalGreer, James C.en
dc.contributor.authorKönig, Christian
dc.contributor.funderScience Foundation Irelanden
dc.contributor.funderIrish Centre for High-End Computingen
dc.date.accessioned2022-01-20T10:15:16Z
dc.date.available2022-01-20T10:15:16Z
dc.date.issued2021
dc.date.submitted2021
dc.description.abstractThis thesis investigates the properties of bismuth (Bi) nanostructures on a fundamental level and in the context of nanoelectronic devices. Due to its unique electronic properties, the material has been studied intensely in the physics community and is well known for its pronounced quantum confinement effect. A semimetal-to-semiconductor transition has been anticipated and discussed for a long time. Since the limitations of conventional silicon technology on the nanometer scale has triggered the search for new materials and device concepts for the semiconductor industry, bismuth has thus attracted even more attention. This thesis is dedicated to studying different aspects of the crystal and electronic structure of bismuth, in particular when grown as a thin film. We discuss how the structure of thin Bi films is affected by the termination with different chemical species. Since the surface-to-volume ratio in nanometer size devices is increased with respect to the macroscopic world, a suitable termination has to be found which can passivate metallic surface states. Otherwise, a band gap which may have opened due to confinement could effectively be closed and disguised. Close to the surface, the particular bilayered structure of the films is perturbed by strong covalent bonds with adsorbates like hydrogen and oxygen. For very thin films a complete reorientation was observed which may prove problematic for applications. We furthermore present a model for the native oxide which has no detrimental effect on the crystal structure of underlying bismuth atomic layers. We investigate how the electronic structure of the bulk material depends on the crystal structure. A good understanding of how the overlap of the valence and conduction states changes as a function of the shape of the unit cell is a useful tool in the interpretation of the electronic structure of thin Bi films which are subject to, e.g., substrate induced strain. In addition to standard methods, we also calculate many-body corrections which are known to vastly improve the prediction of band gaps. Thus, we contribute to the topical and controversial discussion of the band topology in bismuth. The effect of various kinds of surface termination on the electronic structure is discussed. Our calculations show that only the passivation with a single hydrogen atom under idealized conditions is able to open a larger band gap in a very thin (three bilayer thick) film. The oxide interacts only very little with the film. The negligible band gap of the unterminated film however increases with the inclusion of many-body corrections via a G0W0 calculation. These calculations are considered to be more accurate, however we find that the surface states at the M point of the Brillouin zone are better described by density functional theory alone, which may be due to a substrate effect. By means of a constant relaxation time model we show the onset of electronic transport in films with up to 30 bilayers thickness as a function of temperature.en
dc.description.statusNot peer revieweden
dc.description.versionAccepted Versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.citationKönig, C. A. 2021. Design of semimetal electronics relying on the quantum confinement effect. PhD Thesis, University College Cork.en
dc.identifier.endpage154en
dc.identifier.urihttps://hdl.handle.net/10468/12429
dc.language.isoenen
dc.publisherUniversity College Corken
dc.relation.projectinfo:eu-repo/grantAgreement/SFI/SFI Investigator Programme/13/IA/1956/IE/SMALL: Semi-Metal ALL-in-One Technologies/en
dc.rights© 2021, Christian Alexander König.en
dc.rights.urihttps://creativecommons.org/licenses/by-nc-nd/4.0/en
dc.subjectDFTen
dc.subjectGWen
dc.subjectSemimetalen
dc.subjectQuantum confinementen
dc.subjectTopologicalen
dc.subjectTransistoren
dc.subjectBismuthen
dc.subjectFirst principlesen
dc.subjectDensity functional theoryen
dc.subjectElectronic transporten
dc.subjectSurface stateen
dc.subjectSurface passivationen
dc.subjectNanostructureen
dc.subjectMany-body calculationen
dc.titleDesign of semimetal electronics relying on the quantum confinement effecten
dc.typeDoctoral thesisen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD - Doctor of Philosophyen
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