Optical performance of amorphous carbon layers: nonuniformity of transmittance, reflectance, and scattering

Abstract

The optical properties of differently deposited amorphous carbon layers have been investigated by spectrophotometric means from the middle infrared up to the visible spectral region. The optical constants of the layers could be calculated by a numerical procedure which combines features of single-wavelength methods and multi-wavelength methods. Depending on the deposition technique applied, the optical constants of the layers have been found to vary over a wide range. Thus, refractive index values could be established between 1.6 and 2.9, while IR- absorption coefficients vary between 20/cm and 40,000/cm. Thus, the optical performance of the layers is nonuniform and may be influenced by selecting suitable deposition parameters. Due to the potentially wide range of optical constants of amorphous carbon, there are various possibilities for application as an optical thin film material. Applications as selective absorber coatings for solar physical purposes are discussed as well as applications as mechanically and chemically resistant and anti-reflection coatings on high-refractive index semiconducting materials (silicon, germanium).