Initiation strategies for simultaneous control of antiphase domains and stacking faults in GaAs solar cells on Ge

Joseph Faucher, Taizo Masuda, Minjoo Larry Lee

Research output: Contribution to journalArticlepeer-review

Abstract

Incorporating a Ge junction into a lattice-matched GaInP/GaAs/GaInNAsSb triple-junction cell grown by molecular beam epitaxy (MBE) could enable concentrated efficiencies of ∼50%. Epitaxial integration allows lift-off and wafer bonding steps to be avoided, but growth of III-Vs on Ge by MBE can lead to antiphase domains (APD) and stacking fault pyramids (SFP), both of which diminish solar cell performance. Initiating growth by migration-enhanced epitaxy (MEE) is typically cited as necessary to obtain high-quality III-Vs on Ge. In this work, the authors show that typical MEE growth conditions force a compromise between APD height (hAPD) and SFP density (ρSFP). As APDs can readily self-terminate while SFPs cannot, a two-step initiation strategy was employed, where MEE is performed under conditions that minimize ρSFP followed by low-temperature MBE conditions that encourage APD termination. By doing so, the authors obtained ρSFP < 104cm-2 with hAPD ≤ 57 nm. The authors also demonstrated that high-quality GaAs on Ge can be grown without MEE initiation using conventional MBE conditions, though with taller APDs. Both the two-step initiation and conventional MBE initiation yield GaAs cells with high open-circuit voltage and internal quantum efficiency, demonstrating promising paths toward epitaxial integration of high-efficiency solar cells on Ge.

Original languageEnglish (US)
Article number041203
JournalJournal of Vacuum Science and Technology B: Nanotechnology and Microelectronics
Volume34
Issue number4
DOIs
StatePublished - Jul 2016
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Process Chemistry and Technology
  • Surfaces, Coatings and Films
  • Electrical and Electronic Engineering
  • Materials Chemistry

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