Amorphous carbon antireflective coatings in the 10 to 50 μm region of the far-IR

Abstract

The efficiency of far-IR germanium photoconductive detectors can be markedly improved by antireflective coatings. Recently, there has been an effort to develop several micrometer thick, low stress, amorphous carbon films for this purpose. To date, films of no more than 1 to 2 μm have been reported in the literature. In this paper we report the deposition of low stress carbon films which are over 5 μm thick and are effective antireflective coatings at wavelengths of up to Λ = 43 μm. Minimal stress, a requirement for good adhesion, was achieved with a chemical vapor deposition process (CVD) by controlling the hydrocarbon partial pressure (2.2 mTorr) and by doping the carbon film with nitrogen.