Optical-absorption edge and disorder effects in hydrogenated amorphous diamondlike carbon films

摘要

Optical absorption (~1–5 eV) in rf-deposited hydrogenated (20–40 at. %) amorphous “diamondlike” carbon films has been studied as a function of heat treatment. For E \u3e~ 2.5 eV a Tauc behavior is exhibited. Optical band gaps Eg are E0, the width of the tail, is quantitatively explained in terms of the annealing temperature TH. Increasing TH (\u3c700 \u3eK) reduces the hydrogen content, lowers Eg, and appears to harden the films. Eg is determined to be a linear function of E0. Additional analysis was performed in terms of a divergence temperature, T0; the results of this analysis are comparable to those observed in a-Si:H.