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Proceedings Paper

Determination of the optical constants of thin chemical-vapor-deposited diamond windows from 0.5 to 6.5 eV
Author(s): Lawrence H. Robins; Edward N. Farabaugh; Albert Feldman
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Paper Abstract

Transmittance and reflectance spectra of chemical-vapor-deposited (CVD) diamond windows with thicknesses from 0.4 to 1.9 micrometers were measured in the 0.5-6.5 eV photon energy range. The windows were fabricated by microwave-plasma-assisted CVD on silicon substrates, followed by partial removal of the substrates by etching. Three spectra were measured for each window, the reflectance of the top surface, the reflectance of the bottom surface (the surface exposed by etching), and the transmittance. The optical constants were determined as a function of photon energy by fitting the data to a model that includes the effects of surface optical scatter. Root-mean-squared (rms) surface roughness values were also obtained from the analysis. The values of the refractive index (n) were found to be comparable to or slightly less than the values for single-crystal gem diamonds. The values of n were lowest in the most defective films. The absorption coefficient ((alpha) ) differs from that of single-crystal diamond. In some films, substantial absorption occurs in the visible to near- ultraviolet region (2 to 5 eV) where single-crystal diamond is transparent. The spectrum of this low-energy absorption is well-described by the Taucs function, which is used to fit the absorption spectra of 'diamondlike' amorphous carbon materials. There is a steep increase in (alpha) at photon energies at and above the indirect bandgap of diamond (5.5 eV). The absorption rises more steeply from 5.5 to 6.5 eV in these films than in single-crystal diamond, and the shape of the high-energy absorption edge is approximately exponential.

Paper Details

Date Published: 1 December 1991
PDF: 12 pages
Proc. SPIE 1534, Diamond Optics IV, (1 December 1991); doi: 10.1117/12.48284
Show Author Affiliations
Lawrence H. Robins, National Institute of Standards and Technology (United States)
Edward N. Farabaugh, National Institute of Standards and Technology (United States)
Albert Feldman, National Institute of Standards and Technology (United States)

Published in SPIE Proceedings Vol. 1534:
Diamond Optics IV
Albert Feldman; Sandor Holly, Editor(s)

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