{"id":{"repo_id":"bu","oai_identifier":"oai:open.bu.edu:2144/41026"},"canonical_url":"https://search.dev.ndltd.org/etd/bu/oai:open.bu.edu:2144/41026","repository":{"repo_id":"bu","name":"Boston University","base_url":"https://open.bu.edu/oai/request"},"display":{"title":"Optical and electronic properties of defective semiconductors from first principles calculations","abstract":"Defects in semiconductors can play a vital role and even dominate the performance of optoelectronic devices. Thus, understanding the relationship between structural defects and optoelectronic properties is central to the design of new high-performance materials. In this dissertation, we apply state-of-the-art first-principles approaches based on density functional theory (DFT) and many-body perturbation theory (MBPT) to quantitatively describe trap state energies and optical excitation spectra of defective bulk gallium nitride (GaN) and monolayer germanium selenide (GeSe). GaN is a technologically important wide bandgap semiconductor used as a power electronics and blue light emitting material, and naturally contains performance-degrading defects. For GaN containing a charged nitrogen vacancy, we systematically study the trap-state energies and excitonic properties. We benchmark the accuracy of hybrid DFT by comparison to MBPT studies of defective bulk GaN and determine that the HSE functional (Heyd–Scuseria–Ernzerhof) predicts trap-state energies in excellent agreement with MBPT, and that a recently developed solid-state screened range-separated hybrid (SRSH) functional can quantitatively reproduce MBPT-predicted defect energetics, including optical excitations. Additionally, we utilize MBPT to quantify the localization of the Wannier-Mott exciton in the presence of a point defect, introducing an analysis technique of the exciton envelope and center-of-mass functions to extract the Wannier exciton Bohr radius and quantify the perturbation of the exciton wavefunction due to the defect. We then utilize (TD)SRSH to study the excited-state properties of three other important defects in GaN and predict that the carbon impurity may result in the well-known yellow luminescence in bulk GaN. Finally, we apply MBPT with the same analysis techniques developed for GaN to study the optoelectronic properties of defects in monolayer semiconducting GeSe, a material that has promising applications in next-generation optoelectronic devices; we determine that a selenium vacancy strongly modifies the optoelectronic properties of the material. Overall, this dissertation provides a recipe for performing quantitatively accurate MBPT and TDDFT calculations on defective semiconductors, with a systematic study of calculation convergence and defect-defect interactions. Additionally, by an analysis technique of the BSE-computed exciton wavefunction, we introduce a framework for describing defect-induced exciton localization that can be broadly applied to many classes of materials.","abstract_html":"Defects in semiconductors can play a vital role and even dominate the performance of optoelectronic devices. Thus, understanding the relationship between structural defects and optoelectronic properties is central to the design of new high-performance materials. In this dissertation, we apply state-of-the-art first-principles approaches based on density functional theory (DFT) and many-body perturbation theory (MBPT) to quantitatively describe trap state energies and optical excitation spectra of defective bulk gallium nitride (GaN) and monolayer germanium selenide (GeSe). GaN is a technologically important wide bandgap semiconductor used as a power electronics and blue light emitting material, and naturally contains performance-degrading defects. For GaN containing a charged nitrogen vacancy, we systematically study the trap-state energies and excitonic properties. We benchmark the accuracy of hybrid DFT by comparison to MBPT studies of defective bulk GaN and determine that the HSE functional (Heyd–Scuseria–Ernzerhof) predicts trap-state energies in excellent agreement with MBPT, and that a recently developed solid-state screened range-separated hybrid (SRSH) functional can quantitatively reproduce MBPT-predicted defect energetics, including optical excitations. Additionally, we utilize MBPT to quantify the localization of the Wannier-Mott exciton in the presence of a point defect, introducing an analysis technique of the exciton envelope and center-of-mass functions to extract the Wannier exciton Bohr radius and quantify the perturbation of the exciton wavefunction due to the defect. We then utilize (TD)SRSH to study the excited-state properties of three other important defects in GaN and predict that the carbon impurity may result in the well-known yellow luminescence in bulk GaN. Finally, we apply MBPT with the same analysis techniques developed for GaN to study the optoelectronic properties of defects in monolayer semiconducting GeSe, a material that has promising applications in next-generation optoelectronic devices; we determine that a selenium vacancy strongly modifies the optoelectronic properties of the material. Overall, this dissertation provides a recipe for performing quantitatively accurate MBPT and TDDFT calculations on defective semiconductors, with a systematic study of calculation convergence and defect-defect interactions. Additionally, by an analysis technique of the BSE-computed exciton wavefunction, we introduce a framework for describing defect-induced exciton localization that can be broadly applied to many classes of materials.","abstract_has_math":false,"creators":["Lewis, David Kirk"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Sharifzadeh, Sahar"],"committee_chairs":[],"committee_members":[],"year":2020,"date_issued":"2020","date_published":"2020","updated_at":"2026-07-24T01:25:13Z","subjects":["Materials science"],"languages":["en_US"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2144/41026","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Sharifzadeh, Sahar"]},{"key":"dc:creator","label":"Author","values":["Lewis, David Kirk"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2020-05-19T18:28:54Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2020-05-19T18:28:54Z"]},{"key":"dc:date.issued","label":"Date","values":["2020"]},{"key":"dc:type","label":"Dc Type","values":["Thesis/Dissertation"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Materials science"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en_US"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/2144/41026"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Defects in semiconductors can play a vital role and even dominate the performance of optoelectronic devices. Thus, understanding the relationship between structural defects and optoelectronic properties is central to the design of new high-performance materials. In this dissertation, we apply state-of-the-art first-principles approaches based on density functional theory (DFT) and many-body perturbation theory (MBPT) to quantitatively describe trap state energies and optical excitation spectra of defective bulk gallium nitride (GaN) and monolayer germanium selenide (GeSe). GaN is a technologically important wide bandgap semiconductor used as a power electronics and blue light emitting material, and naturally contains performance-degrading defects. For GaN containing a charged nitrogen vacancy, we systematically study the trap-state energies and excitonic properties. We benchmark the accuracy of hybrid DFT by comparison to MBPT studies of defective bulk GaN and determine that the HSE functional (Heyd–Scuseria–Ernzerhof) predicts trap-state energies in excellent agreement with MBPT, and that a recently developed solid-state screened range-separated hybrid (SRSH) functional can quantitatively reproduce MBPT-predicted defect energetics, including optical excitations. Additionally, we utilize MBPT to quantify the localization of the Wannier-Mott exciton in the presence of a point defect, introducing an analysis technique of the exciton envelope and center-of-mass functions to extract the Wannier exciton Bohr radius and quantify the perturbation of the exciton wavefunction due to the defect. We then utilize (TD)SRSH to study the excited-state properties of three other important defects in GaN and predict that the carbon impurity may result in the well-known yellow luminescence in bulk GaN. Finally, we apply MBPT with the same analysis techniques developed for GaN to study the optoelectronic properties of defects in monolayer semiconducting GeSe, a material that has promising applications in next-generation optoelectronic devices; we determine that a selenium vacancy strongly modifies the optoelectronic properties of the material. Overall, this dissertation provides a recipe for performing quantitatively accurate MBPT and TDDFT calculations on defective semiconductors, with a systematic study of calculation convergence and defect-defect interactions. Additionally, by an analysis technique of the BSE-computed exciton wavefunction, we introduce a framework for describing defect-induced exciton localization that can be broadly applied to many classes of materials."]},{"key":"dc:title","label":"Title","values":["Optical and electronic properties of defective semiconductors from first principles calculations"]}]}],"canonical_facts":{"dc:contributor.advisor":["Sharifzadeh, Sahar"],"dc:creator":["Lewis, David Kirk"],"dc:date.accessioned":["2020-05-19T18:28:54Z"],"dc:date.available":["2020-05-19T18:28:54Z"],"dc:date.issued":["2020"],"dc:description.abstract":["Defects in semiconductors can play a vital role and even dominate the performance of optoelectronic devices. Thus, understanding the relationship between structural defects and optoelectronic properties is central to the design of new high-performance materials. In this dissertation, we apply state-of-the-art first-principles approaches based on density functional theory (DFT) and many-body perturbation theory (MBPT) to quantitatively describe trap state energies and optical excitation spectra of defective bulk gallium nitride (GaN) and monolayer germanium selenide (GeSe). GaN is a technologically important wide bandgap semiconductor used as a power electronics and blue light emitting material, and naturally contains performance-degrading defects. For GaN containing a charged nitrogen vacancy, we systematically study the trap-state energies and excitonic properties. We benchmark the accuracy of hybrid DFT by comparison to MBPT studies of defective bulk GaN and determine that the HSE functional (Heyd–Scuseria–Ernzerhof) predicts trap-state energies in excellent agreement with MBPT, and that a recently developed solid-state screened range-separated hybrid (SRSH) functional can quantitatively reproduce MBPT-predicted defect energetics, including optical excitations. Additionally, we utilize MBPT to quantify the localization of the Wannier-Mott exciton in the presence of a point defect, introducing an analysis technique of the exciton envelope and center-of-mass functions to extract the Wannier exciton Bohr radius and quantify the perturbation of the exciton wavefunction due to the defect. We then utilize (TD)SRSH to study the excited-state properties of three other important defects in GaN and predict that the carbon impurity may result in the well-known yellow luminescence in bulk GaN. Finally, we apply MBPT with the same analysis techniques developed for GaN to study the optoelectronic properties of defects in monolayer semiconducting GeSe, a material that has promising applications in next-generation optoelectronic devices; we determine that a selenium vacancy strongly modifies the optoelectronic properties of the material. Overall, this dissertation provides a recipe for performing quantitatively accurate MBPT and TDDFT calculations on defective semiconductors, with a systematic study of calculation convergence and defect-defect interactions. Additionally, by an analysis technique of the BSE-computed exciton wavefunction, we introduce a framework for describing defect-induced exciton localization that can be broadly applied to many classes of materials."],"dc:identifier.uri":["https://hdl.handle.net/2144/41026"],"dc:language.iso":["en_US"],"dc:subject":["Materials science"],"dc:title":["Optical and electronic properties of defective semiconductors from first principles calculations"],"dc:type":["Thesis/Dissertation"]},"updated_at":"2026-07-24T01:25:13Z"}