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I am looking for a material with a refractive index over the visible spectrum , which is close to the refractive index of Si, but which does not oxydise in air.

Do you know of any such material ?

Thank you.

Edit: Some more information. A optical reflector should be build from Si. I will not go into the detail, since it is irrelevant to the question, but I will provide all necessary information. The list is ordered according to importance:

  1. The complex refractive index should be close to Si over the entire visible spectrum
  2. The material should not oxydize in air
  3. The working conditions should be between -30°C to 60°C.
  4. Not necessary, but it would be great if epitaxy on single-crystal silicon is possible.
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    $\begingroup$ $\ce{Si}$ is not transparent and thus can't have refractive index. Did you mean something about reflection? And $\ce{Si}$ doesn't oxidise in air either. $\endgroup$
    – Gert
    Commented Nov 26, 2017 at 17:58
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    $\begingroup$ @Gert Every material has a (complex) refractive index, transparent or not, and Si is very reactive against air and immediately forms an oxide layer on the surface. $\endgroup$
    – Karl
    Commented Nov 26, 2017 at 23:20
  • $\begingroup$ Si might passivate? $\endgroup$
    – Oscar Lanzi
    Commented Nov 27, 2017 at 0:34
  • $\begingroup$ Silicon is one of very few elements (3) with a self-limiting oxide layer. $\endgroup$
    – Jon Custer
    Commented Nov 27, 2017 at 1:13

1 Answer 1

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Over the range of the visible spectrum, ~1.8 - 3.1 eV, or 700-400 nm, the refractive index (nD) of Si varies from about 3.5 - 5, though it is also absorbent and somewhat reflective over that range. Gallium(III) phosphide, $\ce{GaP}$ is one material that comes close to that. It should be fairly stable in air at STP.

Of course, it all depends on your intended use. At what wavelength should nD match that of Si? At what temperature and in what atmosphere will the material be? Does the crystal structure of the material need to match that of Si, so that a regular layer can be deposited? More information is needed for the answer to be of any use.

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  • $\begingroup$ thank you very much for the answer ! This is very informative ! I will add more information to the description of the question. $\endgroup$
    – james
    Commented Nov 27, 2017 at 9:42
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    $\begingroup$ Do you know if epitaxy on single-crystal silicon is possible ? $\endgroup$
    – james
    Commented Nov 27, 2017 at 9:49
  • $\begingroup$ According to ieeexplore.ieee.org/document/5617118 it is feasible despite 0.37% lattice mismatch between Si and GaP. Not much of a gap... $\endgroup$
    – DrMoishe Pippik
    Commented Nov 27, 2017 at 17:44

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