Interdependency of optical constants in alpha-C and alpha-C : H thin filmsinterpreted in light of the density of electronic states

The real and imaginary parts of the dielectric constants for several a-C(:H ) thin films were measured in the energy range 1.5-4.5 eV. The data were an alyzed assuming Gaussian shapes for the "valence" and "conduction'' pi band s and scaling the energy by means of the Gaussian width parameter a. At any given scaled energy Y an approximately linear relationship was obtained be tween the real and the imaginary part of dielectric constant. The energy de pendence of the slope and intercept of such lines are analytically determin ed on the basis of the quoted Gaussian-shaped density of states. The existe nce of a Cauchy behavior for the contribution to the real part of the diele ctric constant due to the transitions other than pi-pi* is shown. The role of disorder in determining the necessity for a scaled energy based analysis was addressed.