# Material with refraction index similar to Si

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.
• $\ce{Si}$ 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. – Gert Nov 26 '17 at 17:58
• @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. – Karl Nov 26 '17 at 23:20
• Si might passivate? – Oscar Lanzi Nov 27 '17 at 0:34
• Silicon is one of very few elements (3) with a self-limiting oxide layer. – Jon Custer Nov 27 '17 at 1:13

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.