Formation of diamond-like carbon films by photoemission-assisted plasma-enhanced chemical vapor deposition

Diamond-like carbon (DLC) films, which are an amorphous carbonaceous allotrope composed of sp² carbon, sp³ carbon, and hydrogen, were prepared by photoemission-assisted plasma-enhanced chemical vapor deposition (PA-PECVD). The electrical behavior during film growth monotonically depended on the methane source gas concentration. Raman analysis of the films suggests that a DLC film grown at a high methane concentration condition contains a small number of graphitic domains, decreasing amorphicity of the film. In contrast, at a low concentration, the methane molecules were transformed into sufficiently fragmented radicals, forming a lot of graphitic nuclei and increasing the amorphicity. However, the variations of the relative dielectric constant, breakdown strength, and optical bandgap exhibited extreme values at an intermediate methane concentration. Thus, the two growth modes give different DLC films with varying combinations of electrical and optical characteristics.