Limitations and possible improvements of DLC dielectric response model based on parameterization of density of states

Several extensions of previously published PDOS model of DLC dielectric response are tested on a typical DLC film on Si. The extended models are applied to the processing of optical measurements, namely UV/VIS/NIR ellipsometry and spectrophotometry as well as FTIR transmittance spectroscopy. The tested extensions of PDOS approach, that originally took into account only π → π⁎ and σ → σ⁎ interband transitions, are (i) the inclusion of π → σ⁎ and σ → π⁎ transitions, (ii) the addition of transitions from σ to bands above σ⁎, (iii) the removal of the assumption that the bands are symmetrical with respect to the Fermi level. However, it is found that these extensions are not needed for the processing of optical data in the measured range, although they could become important in the VUV and XUV regions. It is shown that the PDOS models can be successfully combined with models of phonon absorption in IR region. The application of the combined model in the wide spectral range allows correct calculation of absorption peaks because the interference and dispersion effects are taken into account.