Guided Optimization of Phase-Unstable III–V Compositionally Graded Buffers by Cathodoluminescence Spectrum Imaging

Schulte, Kevin L.; Guthrey, Harvey L.; France, Ryan M.; Geisz, John F.

doi:10.1109/JPHOTOV.2019.2951927

Title: Guided Optimization of Phase-Unstable III–V Compositionally Graded Buffers by Cathodoluminescence Spectrum Imaging

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Abstract

Compositionally graded buffers (CGBs) are essential components of high-efficiency III-V inverted metamorphic solar cells, and high-quality CGBs with low defect densities are a requirement for high device efficiencies. Here, we use plan-view and cross-sectional cathodoluminescence spectrum imaging (CLSI) to investigate the effect of growth conditions on the microstructure of Al_yGa_1-x-yIn_xAS CGBs with x_In > 0.30. CLSI reveals significant compositional fluctuation in these materials that correlates with the distribution of threading dislocations in the CGBs. Threading dislocations are observed to collect in regions between abrupt transitions in emission energy, implying that concomitant strain fluctuations in these regions restrict dislocation motion. Thus, the compositional fluctuation leads to elevated threading dislocation densities that degrade CGB quality. We also correlate compositional fluctuation in the CGB with compositional fluctuation in subsequently grown device layers. The effectiveness of specific growth conditions at suppressing compositional fluctuation and limiting threading dislocation density is evaluated. CGBs grown at high temperatures with high Al content exhibit the lowest defect densities. The use of a high V/III ratio suppresses compositional fluctuation and defect density. In conclusion, these insights lead directly to improvements in the efficiency of metamorphic Ga_1-xIn_xAs solar cells grown on AlyGa_1-x-yIn_xAs CGBs.

Authors:

^[1];

^[1]

National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Publication Date:: Thu Nov 28 00:00:00 EST 2019

Research Org.:: National Renewable Energy Lab. (NREL), Golden, CO (United States)

Sponsoring Org.:: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office

OSTI Identifier:: 1580497

Report Number(s):: NREL/JA-5900-75338
Journal ID: ISSN 2156-3381

Grant/Contract Number:: AC36-08GO28308

Resource Type:: Accepted Manuscript

Journal Name:: IEEE Journal of Photovoltaics

Additional Journal Information:: Journal Volume: 10; Journal Issue: 1; Journal ID: ISSN 2156-3381

Publisher:: IEEE

Country of Publication:: United States

Language:: English

Subject:: 14 SOLAR ENERGY; 36 MATERIALS SCIENCE; indium gallium arsenide; luminescence; photovoltaic cells; scanning electron microscopy

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                    Schulte, Kevin L., Guthrey, Harvey L., France, Ryan M., and Geisz, John F. Guided Optimization of Phase-Unstable III–V Compositionally Graded Buffers by Cathodoluminescence Spectrum Imaging.  United States: N. p., 2019. 
Web.  doi:10.1109/JPHOTOV.2019.2951927.

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                    Schulte, Kevin L., Guthrey, Harvey L., France, Ryan M., & Geisz, John F. Guided Optimization of Phase-Unstable III–V Compositionally Graded Buffers by Cathodoluminescence Spectrum Imaging.  United States.  https://doi.org/10.1109/JPHOTOV.2019.2951927

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                    Schulte, Kevin L., Guthrey, Harvey L., France, Ryan M., and Geisz, John F. Thu .  
"Guided Optimization of Phase-Unstable III–V Compositionally Graded Buffers by Cathodoluminescence Spectrum Imaging".  United States.  https://doi.org/10.1109/JPHOTOV.2019.2951927.  https://www.osti.gov/servlets/purl/1580497.

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@article{osti_1580497,

  title        = {Guided Optimization of Phase-Unstable III–V Compositionally Graded Buffers by Cathodoluminescence Spectrum Imaging},

  author       = {Schulte, Kevin L. and Guthrey, Harvey L. and France, Ryan M. and Geisz, John F.},

  abstractNote = {Compositionally graded buffers (CGBs) are essential components of high-efficiency III-V inverted metamorphic solar cells, and high-quality CGBs with low defect densities are a requirement for high device efficiencies. Here, we use plan-view and cross-sectional cathodoluminescence spectrum imaging (CLSI) to investigate the effect of growth conditions on the microstructure of AlyGa1-x-yInxAS CGBs with xIn > 0.30. CLSI reveals significant compositional fluctuation in these materials that correlates with the distribution of threading dislocations in the CGBs. Threading dislocations are observed to collect in regions between abrupt transitions in emission energy, implying that concomitant strain fluctuations in these regions restrict dislocation motion. Thus, the compositional fluctuation leads to elevated threading dislocation densities that degrade CGB quality. We also correlate compositional fluctuation in the CGB with compositional fluctuation in subsequently grown device layers. The effectiveness of specific growth conditions at suppressing compositional fluctuation and limiting threading dislocation density is evaluated. CGBs grown at high temperatures with high Al content exhibit the lowest defect densities. The use of a high V/III ratio suppresses compositional fluctuation and defect density. In conclusion, these insights lead directly to improvements in the efficiency of metamorphic Ga1-xInxAs solar cells grown on AlyGa1-x-yInxAs CGBs.},

  doi          = {10.1109/JPHOTOV.2019.2951927},

  journal      = {IEEE Journal of Photovoltaics},

  number       = 1,

  volume       = 10,

  place        = {United States},

  year         = {Thu Nov 28 00:00:00 EST 2019},

  month        = {Thu Nov 28 00:00:00 EST 2019}

}

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