{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/127178"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/127178","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Design and growth of wide-bandgap III-V solar cells on silicon by molecular beam epitaxy","abstract":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-03-28 without embargo terms","abstract_html":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-03-28 without embargo terms","abstract_has_math":false,"creators":["Li, Brian Deyuan"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Electrical & Computer Engr","degree_department":null,"school":null,"contributors":["Lee, Minjoo","Choquette, Kent","Dallesasse, John","Kim, Kyekyoon"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-12","date_published":"2024-12","updated_at":"2026-07-22T22:25:03Z","subjects":["Iii-v","Mbe","Gainp","Gaasp","Solar"],"languages":["en","eng"],"rights":["Copyright 2024 Brian Li"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/127178","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Lee, Minjoo","Choquette, Kent","Dallesasse, John","Kim, Kyekyoon"]},{"key":"dc:creator","label":"Author","values":["Li, Brian Deyuan"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2024-12","2024-11-12"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Electrical & Computer Engr"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Iii-v","Mbe","Gainp","Gaasp","Solar"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en","eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2024 Brian Li"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/127178"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-03-28 without embargo terms","The student, Brian Li, accepted the attached license on 2024-11-04 at 10:27.","The student, Brian Li, submitted this Dissertation for approval on 2024-11-04 at 10:50.","This Dissertation was approved for publication on 2024-11-12 at 16:03.","DSpace SAF Submission Ingestion Package generated from Vireo submission #21290 on 2025-03-28 at 14:25:28","Solar energy based on photovoltaic (PV) solar cells is a fast-growing and promising technology to replace fossil fuels in meeting our global electricity demand, as well as a primary energy source for space applications. Silicon (Si) solar cells currently dominate PV production due to their high efficiency (27.1% record under 1-sun illumination) and low cost, but are rapidly reaching their efficiency limit of 29.4%, with little room for further improvement. Increased efficiency can enable lower total PV systems costs by reducing the need for components such as electrical and structural equipment, maintenance, etc. To-date, the highest efficiency solar cells are multi-junction solar cells (MJSC) based on III-V semiconductors with multiple sub-cells stacked from lowest to highest bandgap, with record efficiencies of 39.5% under 1-sun and 47.6% under concentrated light. Unfortunately, III-V MJSCs have orders-of-magnitude greater cost than Si cells, and a major contributor to their cost is growth on lattice-matched GaAs or Ge substrates. A promising approach for increased efficiency at low cost is to grow III-V sub-cells on a low-cost Si substrate for the bottom cell (III-V/Si), which has a theoretical efficiency of > 37% for two-junction cells and > 41% for triple-junction cells. The main drawback of epitaxial growth of III-V/Si MJSCs is the significant lattice mismatch (3-4%) of III-V semiconductors on Si for the materials of interest, causing the formation of extended defects, known as threading dislocations, that propagate through the III-V sub-cells and degrade performance. To date, the highest-efficiency III-V/Si MJSCs have obtained 1-sun efficiencies of 23.4-25.9%, below the record efficiency of a Si cell by itself. Significant research efforts in III-V-on-Si growth have enabled III-V buffers with threading dislocation density (TDD) of ~1.0×107 cm-2 and lower, compared to non-optimized TDD of > 1×109 cm-2. However, even at these lower TDD values, significant research in III-V solar cell growth and design is still needed to improve the efficiency of III-V/Si devices beyond Si alone. A particularly important requirement is to maximize the collection of photo-generated carriers, as described by quantum efficiency, which requires minimizing unwanted recombination losses in the solar cell bulk absorber and at the front and rear surfaces. In this dissertation, I focus on the design, growth and characterization of III-V sub-cells both lattice-matched on GaAs and lattice-mismatched on Si, with the goal of producing cells with superior efficiency for future III-V/Si MJSCs. All devices in this work were grown by molecular beam epitaxy (MBE), and the sub-cells of interest were 1.9 eV Ga0.51In0.49P cells and 1.7 eV GaAs0.77P0.23 cells, which have been used in all record epitaxial III-V/Si MJSCs to-date. For GaInP cells, I first report the use of Tellurium (Te) n-type dopant to obtain superior cell efficiency over Si doping, which can be a complementary or alternative strategy to our existing post-growth annealing approach to improve the quality of MBE-grown phosphides. I then performed a detailed comparative study of GaInP on Si cells with a traditional front-junction design (primarily p-type absorber) and the alternative rear-junction design (primarily n-type absorber) and showed higher material quality for the latter design that should enable improved efficiency of GaInP sub-cells on Si. For GaAsP cells, I performed a detailed design study, but faced significant challenges to further improvement, particularly in quantum efficiency, due to limited material quality in the p-type absorber layer. However, a follow-up study of AlGaAsP distributed Bragg reflectors (DBR) yielded promising results for an alternative path to high carrier collection by rear-surface reflection of photons into a thinned GaAsP cell, with a simulated ~5% boost in efficiency."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Design and growth of wide-bandgap III-V solar cells on silicon by molecular beam epitaxy"]}]}],"canonical_facts":{"dc:contributor":["Lee, Minjoo","Choquette, Kent","Dallesasse, John","Kim, Kyekyoon"],"dc:creator":["Li, Brian Deyuan"],"dc:date":["2024-12","2024-11-12"],"dc:description":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-03-28 without embargo terms","The student, Brian Li, accepted the attached license on 2024-11-04 at 10:27.","The student, Brian Li, submitted this Dissertation for approval on 2024-11-04 at 10:50.","This Dissertation was approved for publication on 2024-11-12 at 16:03.","DSpace SAF Submission Ingestion Package generated from Vireo submission #21290 on 2025-03-28 at 14:25:28","Solar energy based on photovoltaic (PV) solar cells is a fast-growing and promising technology to replace fossil fuels in meeting our global electricity demand, as well as a primary energy source for space applications. Silicon (Si) solar cells currently dominate PV production due to their high efficiency (27.1% record under 1-sun illumination) and low cost, but are rapidly reaching their efficiency limit of 29.4%, with little room for further improvement. Increased efficiency can enable lower total PV systems costs by reducing the need for components such as electrical and structural equipment, maintenance, etc. To-date, the highest efficiency solar cells are multi-junction solar cells (MJSC) based on III-V semiconductors with multiple sub-cells stacked from lowest to highest bandgap, with record efficiencies of 39.5% under 1-sun and 47.6% under concentrated light. Unfortunately, III-V MJSCs have orders-of-magnitude greater cost than Si cells, and a major contributor to their cost is growth on lattice-matched GaAs or Ge substrates. A promising approach for increased efficiency at low cost is to grow III-V sub-cells on a low-cost Si substrate for the bottom cell (III-V/Si), which has a theoretical efficiency of > 37% for two-junction cells and > 41% for triple-junction cells. The main drawback of epitaxial growth of III-V/Si MJSCs is the significant lattice mismatch (3-4%) of III-V semiconductors on Si for the materials of interest, causing the formation of extended defects, known as threading dislocations, that propagate through the III-V sub-cells and degrade performance. To date, the highest-efficiency III-V/Si MJSCs have obtained 1-sun efficiencies of 23.4-25.9%, below the record efficiency of a Si cell by itself. Significant research efforts in III-V-on-Si growth have enabled III-V buffers with threading dislocation density (TDD) of ~1.0×107 cm-2 and lower, compared to non-optimized TDD of > 1×109 cm-2. However, even at these lower TDD values, significant research in III-V solar cell growth and design is still needed to improve the efficiency of III-V/Si devices beyond Si alone. A particularly important requirement is to maximize the collection of photo-generated carriers, as described by quantum efficiency, which requires minimizing unwanted recombination losses in the solar cell bulk absorber and at the front and rear surfaces. In this dissertation, I focus on the design, growth and characterization of III-V sub-cells both lattice-matched on GaAs and lattice-mismatched on Si, with the goal of producing cells with superior efficiency for future III-V/Si MJSCs. All devices in this work were grown by molecular beam epitaxy (MBE), and the sub-cells of interest were 1.9 eV Ga0.51In0.49P cells and 1.7 eV GaAs0.77P0.23 cells, which have been used in all record epitaxial III-V/Si MJSCs to-date. For GaInP cells, I first report the use of Tellurium (Te) n-type dopant to obtain superior cell efficiency over Si doping, which can be a complementary or alternative strategy to our existing post-growth annealing approach to improve the quality of MBE-grown phosphides. I then performed a detailed comparative study of GaInP on Si cells with a traditional front-junction design (primarily p-type absorber) and the alternative rear-junction design (primarily n-type absorber) and showed higher material quality for the latter design that should enable improved efficiency of GaInP sub-cells on Si. For GaAsP cells, I performed a detailed design study, but faced significant challenges to further improvement, particularly in quantum efficiency, due to limited material quality in the p-type absorber layer. However, a follow-up study of AlGaAsP distributed Bragg reflectors (DBR) yielded promising results for an alternative path to high carrier collection by rear-surface reflection of photons into a thinned GaAsP cell, with a simulated ~5% boost in efficiency."],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/127178"],"dc:language":["en","eng"],"dc:rights":["Copyright 2024 Brian Li"],"dc:subject":["Iii-v","Mbe","Gainp","Gaasp","Solar"],"dc:title":["Design and growth of wide-bandgap III-V solar cells on silicon by molecular beam epitaxy"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Electrical & Computer Engr"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:03Z"}