Structural and optical properties of diamond like carbon films

The structural and optical properties of diamond like carbon (DLC) films, prepared by microwave plasma assisted chemical vapour deposition (PACVD) technique are found to be affected by the DC bias applied to the substrate. The structural properties are studied by Raman spectroscopy, while the optical properties in terms of optical band gap (Eg) and band tails (ΔEg) are studied by spectroscopic ellipsometry. The position of G-band and D-band in the Raman spectrum of DLC films is observed to vary with the applied bias voltage. Also, the width of these bands varies with the bias voltage. These effects are explained on the basis of the varying relative fractions of the different phases at different bias voltages. The ellipsometric results are analyzed on the basis of two-layer model. Fraction of voids in the bottom layer varies more widely in comparison to that in the top layer. The values of Eg and ΔEg are observed to vary consistently with the bias voltage. The increase in band gap and the decrease in band tails are explained on the basis of localized states. The Raman spectroscopy results and the ellipsometric results are correlated based on molecular model for hydrogenated DLC films.