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11 September 1989 CVD Diamond For IR Applications
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Abstract
Relatively thick free standing diamond films were grown using a microwave plasma technique and the IR optical absorption coefficient and refractive index determined over the wavelength range from 2.5 to 25 μm. The diamond layers were grown on arsenic doped silicon wafers and the silicon subsequently etched away to leave a free standing diamond layer. Both interference and absorption effects were seen. Interference was observed due to the film thickness of 22.5 ± 1.5 μm and absorptions were seen, characteristic of Type Ilb material, which are believed due to an acceptor impurity, probably aluminum. The absorption coefficient was found to range from 212 cm-1 to 20 cm-1, varying with wavelength with the highest effective energy loss at the high energy end of the spectrum. The effective refractive index also varied from a low of 2.36 to a high of 2.73. This relatively high measured "absorptivity" reflects energy losses arising from all sources including scattering from the relatively rough surface of the as grown film which is suspected to be a primary source of energy loss with unpolished CVD diamond coatings. It is shown here that CVD diamond, unlike most natural diamond, contains substantial amounts of non-diamond carbon and has a complex microstructure which can vary over the thickness of a given coating. Both can contribute to energy losses, particularly if the scale of the microstructure is of the same order as the wavelength of interest.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
W. A. Yarbrough, N. D. Rosen, L. R. Pilione, and W. R. Drawl "CVD Diamond For IR Applications", Proc. SPIE 1112, Window and Dome Technologies and Materials, (11 September 1989); https://doi.org/10.1117/12.960776
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