{"id":{"repo_id":"lancaster","oai_identifier":"oai:eprints.lancs.ac.uk:83166"},"canonical_url":"https://search.dev.ndltd.org/etd/lancaster/oai:eprints.lancs.ac.uk:83166","repository":{"repo_id":"lancaster","name":"Lancaster University","base_url":"https://eprints.lancs.ac.uk/cgi/oai2"},"display":{"title":"Exploring and exploiting charge-carrier confinement in semiconductor nanostructures : heterodimensionality in sub-monolayer InAs in GaAs and photoelectrolysis using type-II heterojunctions","abstract":"In this thesis, semiconductor nanostructures are studied, both experimentally and theoretically, to help aid the development of two diverse and important technologies. Firstly, charge-carrier confinement in stacked sub-monolayer (SML) InAs in GaAs: SML deposition results in the formation of In-rich agglomerations within a lateral InGaAs quantum well (QW) with lower In content. Low-temperature photoluminescence (PL) and magneto-PL reveals strong vertical and weak lateral confinement, indicative of a two-dimensional (2D) excitons. Paradoxically, high-temperature magneto-PL allows excited-state peaks to become resolved, which can be fitted by a Fock-Darwin spectrum, characteristic of a zero-dimensional (0D) system. To solve this contradiction, we postulate that stacked SML InAs in GaAs forms a heterodimensional system, in which electrons are 2D, and see only the lateral InGaAs QW, whilst the heavier holes are 0D, and are confined in the In-rich agglomerations. This description is fully supported by single-particle effective-mass and eight-band k · p calculations, which show heterodimensional confinement is probable for a large variation in In content. SML vertical-cavity surface-emitting lasers (VCSELs) — which prove to be one of the most promising candidates for datacoms applications — have been demonstrated at >20 Gb/s, and we postulate that heterodimensionality is fundamental to this high-speed operation. Efficient carrier injection is achieved by the lack of a wetting layer, along with the 2D electrons coupling to several In-rich agglomerations, making them quickly available to states that are lasing. Furthermore, the shallow confining potential of the In-rich agglomerations means that excess holes cannot build up in states that aren't lasing. Secondly, semiconductor photoelectrolysis for the solar-powered generation of renewable hydrogen by water splitting is researched. The novel use of nanostructures at the semiconductor-electrolyte interface (SEI) in a photoelectrochemical cell (PEC) is proposed to help increase the maximum potential that can be photo-generated, thus increasing the likelihood of a given PEC being able to split water. By solving the Schrödinger, Poisson and drift-diffusion equations, we simulate the band alignment, confined carrier energy states and carrier densities for a variety of different material systems. ZnO quantum dots on InxGa1-xN show the most promising band alignment, with electron-donating and -accepting states straddling the hydrogen- and oxygen-production potentials (respectively) for small x (x < 0.3), indicating an ability to split water.","abstract_html":"In this thesis, semiconductor nanostructures are studied, both experimentally and theoretically, to help aid the development of two diverse and important technologies. Firstly, charge-carrier confinement in stacked sub-monolayer (SML) InAs in GaAs: SML deposition results in the formation of In-rich agglomerations within a lateral InGaAs quantum well (QW) with lower In content. Low-temperature photoluminescence (PL) and magneto-PL reveals strong vertical and weak lateral confinement, indicative of a two-dimensional (2D) excitons. Paradoxically, high-temperature magneto-PL allows excited-state peaks to become resolved, which can be fitted by a Fock-Darwin spectrum, characteristic of a zero-dimensional (0D) system. To solve this contradiction, we postulate that stacked SML InAs in GaAs forms a heterodimensional system, in which electrons are 2D, and see only the lateral InGaAs QW, whilst the heavier holes are 0D, and are confined in the In-rich agglomerations. This description is fully supported by single-particle effective-mass and eight-band k · p calculations, which show heterodimensional confinement is probable for a large variation in In content. SML vertical-cavity surface-emitting lasers (VCSELs) — which prove to be one of the most promising candidates for datacoms applications — have been demonstrated at &gt;20 Gb/s, and we postulate that heterodimensionality is fundamental to this high-speed operation. Efficient carrier injection is achieved by the lack of a wetting layer, along with the 2D electrons coupling to several In-rich agglomerations, making them quickly available to states that are lasing. Furthermore, the shallow confining potential of the In-rich agglomerations means that excess holes cannot build up in states that aren&#x27;t lasing. Secondly, semiconductor photoelectrolysis for the solar-powered generation of renewable hydrogen by water splitting is researched. The novel use of nanostructures at the semiconductor-electrolyte interface (SEI) in a photoelectrochemical cell (PEC) is proposed to help increase the maximum potential that can be photo-generated, thus increasing the likelihood of a given PEC being able to split water. By solving the Schrödinger, Poisson and drift-diffusion equations, we simulate the band alignment, confined carrier energy states and carrier densities for a variety of different material systems. ZnO quantum dots on InxGa1-xN show the most promising band alignment, with electron-donating and -accepting states straddling the hydrogen- and oxygen-production potentials (respectively) for small x (x &lt; 0.3), indicating an ability to split water.","abstract_has_math":false,"creators":["Harrison, Samuel","Hayne, Manus"],"institution":"Lancaster University","degree_name":"Ph.D.","degree_level":"doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2016,"date_issued":"2016-11","date_published":"2016-11","updated_at":"2026-07-24T02:48:32Z","subjects":[],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":null,"outbound_label":null,"outbound_source":null},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Harrison, Samuel","Hayne, Manus"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2016-11-23"]},{"key":"dc:date.issued","label":"Date","values":["2016-11"]},{"key":"dc:publisher.commercial","label":"Dc Publisher Commercial","values":["Lancaster University"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Physics"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["Lancaster University"]},{"key":"dc:relation.isreferencedby","label":"Dc Relation Isreferencedby","values":["https://eprints.lancs.ac.uk/id/eprint/83166/"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Ph.D."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://eprints.lancs.ac.uk/id/eprint/83166/1/2016harrisonphd.pdf"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["In this thesis, semiconductor nanostructures are studied, both experimentally and theoretically, to help aid the development of two diverse and important technologies. Firstly, charge-carrier confinement in stacked sub-monolayer (SML) InAs in GaAs: SML deposition results in the formation of In-rich agglomerations within a lateral InGaAs quantum well (QW) with lower In content. Low-temperature photoluminescence (PL) and magneto-PL reveals strong vertical and weak lateral confinement, indicative of a two-dimensional (2D) excitons. Paradoxically, high-temperature magneto-PL allows excited-state peaks to become resolved, which can be fitted by a Fock-Darwin spectrum, characteristic of a zero-dimensional (0D) system. To solve this contradiction, we postulate that stacked SML InAs in GaAs forms a heterodimensional system, in which electrons are 2D, and see only the lateral InGaAs QW, whilst the heavier holes are 0D, and are confined in the In-rich agglomerations. This description is fully supported by single-particle effective-mass and eight-band k · p calculations, which show heterodimensional confinement is probable for a large variation in In content. SML vertical-cavity surface-emitting lasers (VCSELs) — which prove to be one of the most promising candidates for datacoms applications — have been demonstrated at >20 Gb/s, and we postulate that heterodimensionality is fundamental to this high-speed operation. Efficient carrier injection is achieved by the lack of a wetting layer, along with the 2D electrons coupling to several In-rich agglomerations, making them quickly available to states that are lasing. Furthermore, the shallow confining potential of the In-rich agglomerations means that excess holes cannot build up in states that aren't lasing. Secondly, semiconductor photoelectrolysis for the solar-powered generation of renewable hydrogen by water splitting is researched. The novel use of nanostructures at the semiconductor-electrolyte interface (SEI) in a photoelectrochemical cell (PEC) is proposed to help increase the maximum potential that can be photo-generated, thus increasing the likelihood of a given PEC being able to split water. By solving the Schrödinger, Poisson and drift-diffusion equations, we simulate the band alignment, confined carrier energy states and carrier densities for a variety of different material systems. ZnO quantum dots on InxGa1-xN show the most promising band alignment, with electron-donating and -accepting states straddling the hydrogen- and oxygen-production potentials (respectively) for small x (x < 0.3), indicating an ability to split water."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Exploring and exploiting charge-carrier confinement in semiconductor nanostructures : heterodimensionality in sub-monolayer InAs in GaAs and photoelectrolysis using type-II heterojunctions"]}]}],"canonical_facts":{"dc:creator":["Harrison, Samuel","Hayne, Manus"],"dc:date":["2016-11-23"],"dc:date.issued":["2016-11"],"dc:description.abstract":["In this thesis, semiconductor nanostructures are studied, both experimentally and theoretically, to help aid the development of two diverse and important technologies. Firstly, charge-carrier confinement in stacked sub-monolayer (SML) InAs in GaAs: SML deposition results in the formation of In-rich agglomerations within a lateral InGaAs quantum well (QW) with lower In content. Low-temperature photoluminescence (PL) and magneto-PL reveals strong vertical and weak lateral confinement, indicative of a two-dimensional (2D) excitons. Paradoxically, high-temperature magneto-PL allows excited-state peaks to become resolved, which can be fitted by a Fock-Darwin spectrum, characteristic of a zero-dimensional (0D) system. To solve this contradiction, we postulate that stacked SML InAs in GaAs forms a heterodimensional system, in which electrons are 2D, and see only the lateral InGaAs QW, whilst the heavier holes are 0D, and are confined in the In-rich agglomerations. This description is fully supported by single-particle effective-mass and eight-band k · p calculations, which show heterodimensional confinement is probable for a large variation in In content. SML vertical-cavity surface-emitting lasers (VCSELs) — which prove to be one of the most promising candidates for datacoms applications — have been demonstrated at >20 Gb/s, and we postulate that heterodimensionality is fundamental to this high-speed operation. Efficient carrier injection is achieved by the lack of a wetting layer, along with the 2D electrons coupling to several In-rich agglomerations, making them quickly available to states that are lasing. Furthermore, the shallow confining potential of the In-rich agglomerations means that excess holes cannot build up in states that aren't lasing. Secondly, semiconductor photoelectrolysis for the solar-powered generation of renewable hydrogen by water splitting is researched. The novel use of nanostructures at the semiconductor-electrolyte interface (SEI) in a photoelectrochemical cell (PEC) is proposed to help increase the maximum potential that can be photo-generated, thus increasing the likelihood of a given PEC being able to split water. By solving the Schrödinger, Poisson and drift-diffusion equations, we simulate the band alignment, confined carrier energy states and carrier densities for a variety of different material systems. ZnO quantum dots on InxGa1-xN show the most promising band alignment, with electron-donating and -accepting states straddling the hydrogen- and oxygen-production potentials (respectively) for small x (x < 0.3), indicating an ability to split water."],"dc:format":["application/pdf"],"dc:identifier.uri":["https://eprints.lancs.ac.uk/id/eprint/83166/1/2016harrisonphd.pdf"],"dc:publisher.commercial":["Lancaster University"],"dc:publisher.department":["Physics"],"dc:publisher.institution":["Lancaster University"],"dc:relation.isreferencedby":["https://eprints.lancs.ac.uk/id/eprint/83166/"],"dc:title":["Exploring and exploiting charge-carrier confinement in semiconductor nanostructures : heterodimensionality in sub-monolayer InAs in GaAs and photoelectrolysis using type-II heterojunctions"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["doctoral"],"dc:type.qualificationname":["Ph.D."]},"updated_at":"2026-07-24T02:48:32Z"}