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Jurgen Michel and Juejun Hu. Zhao, Xueying,Ph.D.Massachusetts Institute of Technology. Massachusetts Institute of Technology. Department of Materials Science and Engineering. Massachusetts Institute of Technology. Department of Materials Science and Engineering 2021-01-05T23:12:30Z 2021-01-05T23:12:30Z 2020 2020 https://hdl.handle.net/1721.1/129005 1227036990 Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2020 Cataloged from student-submitted PDF of thesis. Includes bibliographical references (pages 79-86). Lateral multijunction photovoltaics based on III-V direct band gap semiconductors enable efficient energy conversion. However, lattice matching between cell and substrate requires the use of expensive Ge or III-V substrates, which limits widespread application of III-V solar cells. Cost reduction can be achieved by using Ge-on-Si virtual substrate where a thin layer of Ge is grown on relatively inexpensive Si substrates, thanks to the greater material abundance and larger wafer diameters of Si. However, the lattice mismatch between Si and Ge can bring about threading dislocations that can significantly impair the efficiency of solar cells. This thesis presents patterned epitaxial growth of pure Ge on Si wafer through ultra-high vacuum chemical vapor deposition that achieves low threading dislocation density. This unlocks the potential for growing lattice-matched III-V photovoltaics of high quality on top of the virtual substrate. In addition, this thesis seeks to understand the mechanisms behind trapping of dislocations. The dislocation studies in this thesis not only shed light on dislocation motion in the Ge-on-Si epitaxy, but can be applied to other lattice mismatched materials systems as well. Lastly, the potential of lateral multijunction photovoltaics is demonstrated through simulation approaches. by Xueying Zhao. Ph.D. Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering 86 pages eng Massachusetts Institute of Technology MIT theses may be protected by copyright. Please reuse MIT thesis content according to the MIT Libraries Permissions Policy, which is available through the URL provided. http://dspace.mit.edu/handle/1721.1/7582 Materials Science and Engineering. Germanium-on-silicon virtual substrate for lateral multijunction photovoltaics Thesis application/pdf 2021-01-05T23:12:29Z Publication Doctoral MatSci unknown unknown <Publication xmlns="https://www.openaire.eu/cerif-profile/1.1/" id="a87dbded-d167-4495-b7e3-80073fc39a44"> <Type xmlns="https://www.openaire.eu/cerif-profile/vocab/COAR_Publication_Types">http://purl.org/coar/resource_type/c_1843</Type> <Language>eng</Language> <Title>Germanium-on-silicon virtual substrate for lateral multijunction photovoltaics</Title> <PublishedIn> <Publication> </Publication> </PublishedIn> <PublicationDate>2020</PublicationDate> <Authors> <Author> <DisplayName>Zhao, Xueying,Ph.D.Massachusetts Institute of Technology.</DisplayName> <Affiliation> <OrgUnit> </OrgUnit> </Affiliation> </Author> </Authors> <Editors> </Editors> <Publishers> <Publisher> <DisplayName>Massachusetts Institute of Technology</DisplayName> <OrgUnit /> </Publisher> </Publishers> <License>http://dspace.mit.edu/handle/1721.1/7582</License> <Keyword>Materials Science and Engineering.</Keyword> <Abstract>Lateral multijunction photovoltaics based on III-V direct band gap semiconductors enable efficient energy conversion. However, lattice matching between cell and substrate requires the use of expensive Ge or III-V substrates, which limits widespread application of III-V solar cells. Cost reduction can be achieved by using Ge-on-Si virtual substrate where a thin layer of Ge is grown on relatively inexpensive Si substrates, thanks to the greater material abundance and larger wafer diameters of Si. However, the lattice mismatch between Si and Ge can bring about threading dislocations that can significantly impair the efficiency of solar cells. This thesis presents patterned epitaxial growth of pure Ge on Si wafer through ultra-high vacuum chemical vapor deposition that achieves low threading dislocation density. This unlocks the potential for growing lattice-matched III-V photovoltaics of high quality on top of the virtual substrate. In addition, this thesis seeks to understand the mechanisms behind trapping of dislocations. The dislocation studies in this thesis not only shed light on dislocation motion in the Ge-on-Si epitaxy, but can be applied to other lattice mismatched materials systems as well. Lastly, the potential of lateral multijunction photovoltaics is demonstrated through simulation approaches.</Abstract> <Access xmlns="http://purl.org/coar/access_right" > </Access> </Publication>