Spectroscopic ellipsometry of columnar porous Si thin films and Si nanowires

Bálint Fodor, Thomas Defforge, Emil Agócs, Miklós Fried, Gaël Gautier, Péter Petrik

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Columnar mesoporous Si thin films and dense nanowire (SiNW) carpets were investigated by spectroscopic ellipsometry in the visible-near-infrared wavelength range. Porous Si layers were formed by electrochemical etching while structural anisotropy was controlled by the applied current. Layers of highly oriented SiNWs, with length up to 4.1 μm were synthesized by metal-assisted chemical etching. Ellipsometric spectra were fitted with different multi-layered, effective medium approximation-based (EMA) models. Isotropic, in-depth graded, anisotropic and hybrid EMA models were investigated with the help of the root mean square errors obtained from the fits. Ellipsometric-fitted layer thicknesses were also cross-checked by scanning electron microscopy showing an excellent agreement. Furthermore, in the case of mesoporous silicon, characterization also revealed that, at low current densities (<100 mA/cm 2 ), in-depth inhomogeneity shows a more important feature in the ellipsometric spectra than anisotropy. On the other hand, at high current densities (>100 mA/cm 2 ) this behavior turns around, and anisotropy becomes the dominant feature describing the spectra. Characterization of SiNW layers showed a very high geometrical anisotropy. However, the highest fitted geometrical anisotropy was obtained for the layer composed of ∼1 μm long SiNWs indicating that for thicker layers, collapse of the nanowires occurs.

Original languageEnglish
Pages (from-to)397-404
Number of pages8
JournalApplied Surface Science
Volume421
DOIs
Publication statusPublished - Nov 1 2017

Keywords

  • Anisotropy
  • Birefringence
  • Effective medium approximation
  • In-depth gradient
  • Morphology
  • Porous silicon layer
  • Silicon nanowires
  • Spectroscopic ellipsometry

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics
  • Physics and Astronomy(all)
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films

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