Electronic density of states and deep defects of hydrogenated amorphous carbon (a-C:H)

Abstract R.f. plasma chemical vapour deposition was used to prepare hydrogenated amorphous carbon (a-C:H) films with properties ranging from polymer-like to diamond-like carbon (DLC) depending on self bias ranging from 0 to 200 V. The films were characterized by their C 1s plasmon loss which yields the density and by optical properties such as the refractive index and the optical gap which decreases from 4.0 to 1.9 eV on bias. UV photoemission spectra were used to derive relative sp 2 -contents which increase from 14% for polymer-like material to 37% for DLC. Two defect bands in the pseudogap with binding energies of 1.8 eV and 0.8 eV and an integrated electron density that increases with bias from 1 × 10 20 cm −3 to 7 × 10 20 cm −3 were identified with photoelectron yield spectroscopy. Transient changes in the deep defects of DLC on illumination with 680 nm wavelength light were observed and are discussed.