OPTICAL AND ELECTRONIC-PROPERTIES OF NITROGEN-IMPLANTED DIAMOND-LIKE CARBON-FILMS

Optical and electrical measurements on nitrogen ion-implanted diamond- like carbon films are presented. Raman scattering measurements, which probe the crystallinity of the film surface, indicate that nitrogen im plantation reduces the finite crystallographic order in the pristine c arbon films. The absence of molecular vibrations in the infrared absor ption spectra of the films argues against a polymeric structure of the ion-implanted films. Spectroscopic ellipsometry experiments determine the change in the optical constants of the carbon film due to nitroge n implantation. Electrical de conductivity measurements are interprete d within the framework of a schematic density of states picture of gra phitic pi-electrons in an amorphous carbon system. Taken collectively, the optical and electrical measurements suggest that nitrogen implant ation increases the density of localized states within the 1.5 eV band gap of the quasi-amorphous carbon film, thereby reducing the bandgap a nd increasing the conductivity of the nitrogen-implanted films.