I have deposited amorphous silicon thin film (appx. 100 nm) using PVD technique. Initial deposition trials were on silicon substrate and hardly I could differentiate the colour of thin film and the substrate. To cross-check whether the deposition is happening, I have deposited the same on glass substrate. The film looked slightly brownish colour but was almost transparent. The deposition temperature was 200 degree Celsius. Anyone had the same experience?
Yes, amorphous Silicon films normally look brownish, and can have some transparency. As you increase the film thickness, the transparency will decrease.
You can use UV-Visible spectroscopy, in the transmission mode,
you can then figure out the optical transimission percentage through your film, and
also determine the optical absorption edge for your 100 nm thick films.
In the literature lyou will find many paper paper on the optical properlties of amorphous Si films prepared by different techniques.
K. Sreenivas
Dear Jose.
This is a very good question.
In silicon absorption edge is on the border of the visible range.
I've been trying to convince, the film and the crystal is not the same thing.
Further, let alone "color." A gold film have different colors depending on the thickness and viewing angle.
Thus, we continue to work with amorphous silicon. Using all known and unknown techniques. That's all.
Yours sincerely, M.K.
Thank you Mr. Myroslav :)
Nice to hear from you. We also work on different thin films for MEMS applications.
Even a-Si also shows different colours at different viewing angles. But when we look perpendicular to the substrate, the colour is light brown.
Jose
A-Si:H is a semiconductor with an E04 bandgap(the photon energy at which the absorption is 1x10^4/cm) of ~1.95-2.0 eV. That means that it will transmit deep red photons, but absorb blue and green if it is thick. If the film is very thin (10nm), it will transmit most visible wavelengths fairly well, except for near uv. The transmission of the film depends on what wavelength and what thickness of the film you are talking about. You can look up the absorption coefficients in any good paper or book on a-Si (eg Dr. Robert Street's book- which is an excellent treatment of the subject).
May be these pictures can be useful. Source: Google pictures for "absorption coeff of a-Si"
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