Using Electron Channeling Contrast Imaging to Inform and Improve the Growth of High-Efficiency GaAs Solar Cells on Nanopatterned GaAs Substrates

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Abstract

Patterned substrates provide opportunities for reducing the cost of high-efficiency III-V devices by incorporating mechanically weak layers beneficial for substrate reuse (e.g. by spalling). In this work, the functionality of electron channeling contrast imaging (ECCI) as a tool to efficiently understand and mitigate defect formation is exemplified by developing a process in which high-quality III-V material can be grown on nanopatterned GaAs substrates. Reactive ion etching used in the patterning process was found to damage the GaAs substrate surface, leading to the formation of stacking faults in the epitaxial material as observed by ECCI. Etching the patterned substrates in a 1 NH4OH: 1 H2O2: 50 DI H2O solution for 10 s prior to growth removed the substrate surface damage and stacking faults were no longer present. Growth of solar cell device structures initially produced samples with many macroscale flaws creating shunts in the devices, which complicated the assessment of material quality by device measurements. However, ECCI revealed that the epitaxial material surrounding macroscale flaws was free from any crystallographic defects such as stacking faults and threading dislocations. With this knowledge, we focused on refining the patterning process to eliminate the macroscale flaws. Solar cells were then grown on the improved nanopatterned substrates and exhibited device structures with defect densities less than 5 × 105 cm−2 and average conversion efficiency of 24.8%, nearly identical to devices grown on unpatterned epi-ready substrates (25.0%).

Original languageAmerican English
Article numberArticle No. 126490
Number of pages5
JournalJournal of Crystal Growth
Volume581
DOIs
StatePublished - 1 Mar 2022

Bibliographical note

Publisher Copyright:
© 2021

NREL Publication Number

  • NREL/JA-5900-81191

Keywords

  • crystalline defects
  • electron channeling contrast imaging
  • metalorganic vapor phase epitaxy
  • selective epitaxy
  • semiconducting III-V materials
  • solar cells

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