Diamondlike amorphous hydrogenated carbon (a-.C:H) films have found widespread use as hard coatings for IR optical applications. The refractive index of these films (n=2) allows the deposition of quarter-wave antireflection coatings on germanium. More complex optical designs, however, require the extension of the range of the optical constants. For this reason we studied amorphous hydrogenated carbon-germanium alloys. The corresponding a-C1 xc3ex H films with 0 < X < 1 were grown by ri-plasma deposition using mixtures of a hydrocarbon gas and germane or tetramethylgermanium (TMG) as precursors. Film composition, refractive index and IR absorption spectra were measured. This material system offers the possibility to adjust. the refractive index between 1 .8 and 4.1 and thus allows the deposition of multilayer thin film systems for IR optical applications. As a result of numerical design calculations, a three layer structure with a hard a-C:H top layer is proposed, which acts as a broadband antireflection coating on germanium substrates for 8-1 2 j.m. We report on the growth and performance of these hard multilayer AR coatings.

Date Published: 1 August 1990
PDF: 7 pages
Proc. SPIE 1275, Hard Materials in Optics, (1 August 1990); doi: 10.1117/12.20517

Published in SPIE Proceedings Vol. 1275:
Hard Materials in Optics
Carl-Gustaf Ribbing, Editor(s)