Dielectric functions of a-Si1-xGex:H versus ge content, temperature, and processing: Advances in optical function parameterization

Nikolas J. Podraza, Christopher R. Wronski, Mark W. Horn, Robert W. Collins

Research output: Chapter in Book/Report/Conference proceedingConference contribution

15 Scopus citations


We have applied an advanced model to analyze the dielectric functions ε = ε1 + iε2 of amorphous silicon-germanium alloys (a-Si1-xGex:H) (i) as a function of alloy content x by varying the flow ratio G = [GeH4]/{[SiH4]+[GeH 4]} in plasma-enhanced chemical vapor deposition (PECVD), and (ii) for the first time as a function of the measurement temperature Tm by cooling the newly-deposited film. All ε spectra (1.5-4.5 eV) have been measured by spectroscopic ellipsometry (SE) either in real time during deposition or in situ post-deposition in order to avoid surface contamination. From the resulting extensive database, the optical properties of the alloys can be predicted for any value x and Tm within the ranges of the database. Such a capability is expected to be useful, for example, in real time control of optical gap in the PECVD process and in predicting the quantum efficiency of multijunction a-Si:H-based solar cells versus operating temperature. The effect on the database of other deposition parameters such as the electrode configuration and the H2-dilution ratio R = [H2]/ {[SiH4] + [GeH4]} have also been explored. The latter two studies provide useful insights into materials properties that can be extracted from a single spectroscopic measurement performed in real time during PECVD. For example, the energy width of the resonance in ε correlates closely with the precursor surface diffusion characteristics observed throughout growth - both determined from real time SE. This result indicates that short-range ordering in the film is improved when surface diffusion is promoted.

Original languageEnglish (US)
Title of host publicationAmorphous and Polycrystalline Thin-Film Silicon Science and Technology - 2006
Number of pages6
StatePublished - 2007
Event2006 MRS Spring Meeting - San Francisco, CA, United States
Duration: Apr 18 2006Apr 21 2006

Publication series

NameMaterials Research Society Symposium Proceedings
ISSN (Print)0272-9172


Other2006 MRS Spring Meeting
Country/TerritoryUnited States
CitySan Francisco, CA

All Science Journal Classification (ASJC) codes

  • General Materials Science
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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