Optical and electrical properties of amorphous hydrogenated carbon layers deposited by dc plasma decomposition

Abstract The optical properties of hard dc plasma deposited amorphous carbon layers have been investigated from the middle IR up to the visible spectral region. Refractive indices and absorption coefficient behaviour have been determined by means of spectral transmittance and reflectance measurements. The layers show a transparency window in the middle IR in the wavenumber range 1700 cm −1 v −1 . The refractive indices in the “window” region are between 2.1 and 2.3 with weak dispersion. IR-absorption losses have been discussed in terms of a dispersion model, considering the absorption detected to be caused by a superposition of Lorentz-lines and an Urbach-part. Planar and transverse conductivities of the layers have been determined at room temperature. In addition, the conductivity of representative samples has been investigated in dependence of the temperature in the range of 80 K up to 350 K. A correlation between the thus-obtained activation energies for thermally-activated hopping in the band tails and the Urbach parameters of the layers could be established.