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Jacob Boyer Dissertation Final.pdf (367.89 MB)

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Epitaxy and Characterization of Metamorphic Semiconductors for III-V/Si Multijunction Photovoltaics

Boyer, Jacob Tyler
http://orcid.org/0000-0001-7046-0561
http://rave.ohiolink.edu/etdc/view?acc_num=osu1607042647720476

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
III-V/Si multijunction photovoltaics possess the potential for high power conversion efficiencies (surpassing the single-junction limit) at low cost by leveraging the inexpensive and scalable Si platform. Both space and terrestrial markets can benefit from this technology; however, multiple materials-related obstacles must first be overcome in order to truly demonstrate this potential and enable adoption of this new technology. For terrestrial usage, low-cost III-V deposition techniques are necessary to remain cost competitive with current photovoltaics. Given a Si bottom cell, the optimal series-connected dual-junction photovoltaic efficiency for both space and terrestrial solar spectra is achieved with a 1.7-1.8 eV top cell, which is most conveniently provided by GaAsyP1-y (y ~0.7-0.8) at around 3% lattice mismatch to the Si substrate. While epitaxial integration of GaAsyP1-y alloys on Si is favorable over high-cost and non-scalable wafer bonding or stacking techniques, controlling (minimizing) dislocation content within the strain-relaxed metamorphic materials, and/or minimizing its impact on top cell performance via careful device design, is key to achieving optimal performance. Materials challenges related to the heterovalent, lattice-mismatched GaP/Si interface and the thermal expansion coefficient mismatch of GaAsyP1-y to Si all complicate the production of low-defect density GaAsyP1-y materials. To this end, we have undertaken metalorganic chemical vapor deposition (MOCVD) growth studies of GaP/Si nucleation layers and GaAsyP1-y step-graded buffers, demonstrating substantial progress by reducing defect densities by over an order of magnitude in the course of this recent work. These efforts have largely been enabled via rapid feedback regarding crystalline defect populations obtained from electron channeling contrast imaging (ECCI). From these experimental studies, a deeper understanding of dislocation dynamics in these metamorphic materials is reached via quantitative analysis and modeling. As a result, successful demonstration of defect density reductions over an order of magnitude have been demonstrated in GaAsyP1-y/GaP/Si materials tailored to the requirements of III-V/Si photovoltaic devices. This achievement in material quality enables further production and development of high efficiency III-V/Si photovoltaic devices with rapid improvements at the newly achieved defect levels.
Tyler Grassman (Advisor)
Suliman Dregia (Committee Member)
Michael Mills (Committee Member)
Roberto Myers (Committee Member)
Materials Science
Heteroepitaxy; metamorphic semiconductors; III-V on Si; dislocations; epitaxial growth; electron channeling contrast imaging; photovoltaics; MOCVD; GaP on Si; GaAsP on Si; TDD

Recommended Citations

Citations

  • Boyer, J. T. (2020). Epitaxy and Characterization of Metamorphic Semiconductors for III-V/Si Multijunction Photovoltaics [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1607042647720476

    APA Style (7th edition)

  • Boyer, Jacob. Epitaxy and Characterization of Metamorphic Semiconductors for III-V/Si Multijunction Photovoltaics. 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1607042647720476.

    MLA Style (8th edition)

  • Boyer, Jacob. "Epitaxy and Characterization of Metamorphic Semiconductors for III-V/Si Multijunction Photovoltaics." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1607042647720476

    Chicago Manual of Style (17th edition)

osu1607042647720476
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