Nanostructured Black Silicon and the Optical Reflectance of Graded-Density Surfaces

Howard M. Branz, Vernon E. Yost, Scott Ward, Kim M. Jones, Bobby To, Paul Stradins

Research output: Contribution to journalArticlepeer-review

292 Scopus Citations


We fabricate and measure graded-index "black silicon" surfaces and find the underlying scaling law governing reflectance. Wet etching (100) silicon in HAuCl4, HF, and H2 O2 produces Au nanoparticles that catalyze formation of a network of [100]-oriented nanopores. This network grades the near-surface optical constants and reduces reflectance to below 2% at wavelengths from 300 to 1000 nm. As the density-grade depth increases, reflectance decreases exponentially with a characteristic grade depth of about 1/8 the vacuum wavelength or half the wavelength in Si. Observation of Au nanoparticles at the ends of cylindrical nanopores confirms local catalytic action of moving Au nanoparticles.

Original languageAmerican English
Article numberArticle No. 231121
Number of pages3
JournalApplied Physics Letters
Issue number23
StatePublished - 2009

NREL Publication Number

  • NREL/JA-520-45395


  • photovoltaic cells
  • reflectance


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